diff --git a/e2e/fixtures/keyword-research-fixtures.ts b/e2e/fixtures/keyword-research-fixtures.ts
index aa53d9b..fa8bf84 100644
--- a/e2e/fixtures/keyword-research-fixtures.ts
+++ b/e2e/fixtures/keyword-research-fixtures.ts
@@ -1,5 +1,5 @@
 import type { KeywordResearchRow } from "@/types/keywords";
-import type { ResearchKeywordsInput } from "@/types/schemas/keywords";
+import type { ResolvedResearchKeywordsInput } from "@/types/schemas/keywords";
 
 const MONTHLY_SEARCHES = [
   { year: 2025, month: 4, searchVolume: 1200 },
@@ -33,7 +33,7 @@ function makeRow(
   };
 }
 
-export function getKeywordResearchFixture(data: ResearchKeywordsInput) {
+export function getKeywordResearchFixture(data: ResolvedResearchKeywordsInput) {
   const seedKeyword = data.keywords[0] ?? "keyword research";
   const rows = [
     makeRow(seedKeyword, 0, {
diff --git a/src/client/features/domain/DomainOverviewPage.tsx b/src/client/features/domain/DomainOverviewPage.tsx
index 70843d0..c782046 100644
--- a/src/client/features/domain/DomainOverviewPage.tsx
+++ b/src/client/features/domain/DomainOverviewPage.tsx
@@ -8,9 +8,7 @@ import {
   type DomainSearchParams,
 } from "@/types/schemas/domain";
 import {
-  DEFAULT_LOCATION_CODE,
   LOCATIONS,
-  getLanguageCode,
   isLabsLocationCode,
 } from "@/client/features/keywords/locations";
 import { useDomainSearchHistory } from "@/client/hooks/useDomainSearchHistory";
@@ -80,10 +78,13 @@ function getSortSearchUpdate(
   };
 }
 
-function getLocationSearchUpdate(nextLocationCode: number): DomainSearchUpdate {
+function getLocationSearchUpdate(
+  nextLocationCode: number,
+  defaultLocationCode: number,
+): DomainSearchUpdate {
   return {
     loc:
-      nextLocationCode === DEFAULT_LOCATION_CODE ? undefined : nextLocationCode,
+      nextLocationCode === defaultLocationCode ? undefined : nextLocationCode,
     page: undefined,
   };
 }
@@ -122,11 +123,12 @@ function getTabSearchUpdate(
 
 function getHistorySearchUpdate(
   item: DomainSearchHistoryItem,
+  defaultLocationCode: number,
 ): DomainSearchUpdate {
   const historyLocation =
     item.locationCode != null && isLabsLocationCode(item.locationCode)
       ? item.locationCode
-      : DEFAULT_LOCATION_CODE;
+      : defaultLocationCode;
 
   return {
     ...buildDomainFiltersClearSearchUpdate(),
@@ -135,8 +137,7 @@ function getHistorySearchUpdate(
     sort: toSortSearchParam(item.sort),
     order: undefined,
     tab: item.tab === "keywords" ? undefined : item.tab,
-    loc:
-      historyLocation === DEFAULT_LOCATION_CODE ? undefined : historyLocation,
+    loc: historyLocation === defaultLocationCode ? undefined : historyLocation,
     size: undefined,
   };
 }
@@ -148,6 +149,7 @@ function getSearchSubmitUpdate({
   locationCode,
   currentOrder,
   activeTab,
+  defaultLocationCode,
 }: {
   domain: string;
   subdomains: boolean;
@@ -155,6 +157,7 @@ function getSearchSubmitUpdate({
   locationCode: number;
   currentOrder: SortOrder;
   activeTab: DomainActiveTab;
+  defaultLocationCode: number;
 }): DomainSearchUpdate {
   return {
     ...buildDomainFiltersClearSearchUpdate(),
@@ -163,7 +166,7 @@ function getSearchSubmitUpdate({
     sort: toSortSearchParam(sort),
     order: toSortOrderSearchParam(sort, currentOrder),
     tab: activeTab === "keywords" ? undefined : activeTab,
-    loc: locationCode === DEFAULT_LOCATION_CODE ? undefined : locationCode,
+    loc: locationCode === defaultLocationCode ? undefined : locationCode,
     size: undefined,
   };
 }
@@ -205,9 +208,14 @@ function useDomainOverviewState({
 
   const applyLocationChange = useCallback(
     (nextLocationCode: number) => {
-      setSearchParams(getLocationSearchUpdate(nextLocationCode));
+      setSearchParams(
+        getLocationSearchUpdate(
+          nextLocationCode,
+          routeState.defaultLocationCode,
+        ),
+      );
     },
-    [setSearchParams],
+    [routeState.defaultLocationCode, setSearchParams],
   );
 
   const handleSortColumnClick = useCallback(
@@ -246,21 +254,21 @@ function useDomainOverviewState({
 
   const handleHistorySelect = useCallback(
     (item: DomainSearchHistoryItem) => {
-      setSearchParams(getHistorySearchUpdate(item));
+      setSearchParams(
+        getHistorySearchUpdate(item, routeState.defaultLocationCode),
+      );
     },
-    [setSearchParams],
+    [routeState.defaultLocationCode, setSearchParams],
   );
 
-  const languageCode = getLanguageCode(routeState.locationCode);
   const overviewQuery = useDomainOverviewQuery({
     projectId,
     domain: routeState.domain,
     includeSubdomains: routeState.subdomains,
-    locationCode: routeState.locationCode,
-    languageCode,
+    locationCode: routeState.sentLocationCode,
   });
   const overview = overviewQuery.data ?? null;
-  const isLoading = overviewQuery.isLoading;
+  const isLoading = routeState.domain.trim() !== "" && overviewQuery.isLoading;
 
   const controlsForm = useForm({
     defaultValues: {
@@ -290,6 +298,7 @@ function useDomainOverviewState({
           locationCode: value.locationCode,
           currentOrder: routeState.order,
           activeTab: routeState.tab,
+          defaultLocationCode: routeState.defaultLocationCode,
         }),
       );
     },
@@ -389,7 +398,6 @@ function useDomainOverviewState({
     history,
     historyLoaded,
     removeHistoryItem,
-    languageCode,
     setSearchParams,
     applySort,
     applyLocationChange,
@@ -412,16 +420,20 @@ export function DomainOverviewPage({
   navigate,
   onShowRecentSearches,
 }: Props) {
-  const state = useDomainOverviewState({ navigate, routeState, projectId });
+  const state = useDomainOverviewState({
+    navigate,
+    routeState,
+    projectId,
+  });
   const urlTabInput = useMemo<SearchTabInput | null>(() => {
     if (routeState.domain.trim() === "") return null;
     return {
       type: "domain",
       domain: routeState.domain,
       subdomains: routeState.subdomains,
-      locationCode: routeState.locationCode,
+      locationCode: routeState.sentLocationCode,
     };
-  }, [routeState.domain, routeState.locationCode, routeState.subdomains]);
+  }, [routeState.domain, routeState.sentLocationCode, routeState.subdomains]);
 
   const navigateToSearchTab = useCallback(
     (input: SearchTabInput | null) => {
@@ -443,10 +455,7 @@ export function DomainOverviewPage({
           order: undefined,
           tab: undefined,
           page: undefined,
-          loc:
-            input.locationCode === DEFAULT_LOCATION_CODE
-              ? undefined
-              : input.locationCode,
+          loc: input.locationCode,
           size: undefined,
         }),
         replace: true,
@@ -458,14 +467,18 @@ export function DomainOverviewPage({
   const searchTabs = useSearchTabNavigation({
     storageKey: `domain:${projectId}`,
     urlInput: urlTabInput,
-    getLabel: useCallback((input) => {
-      if (input.type !== "domain") return "";
-      const locationSuffix =
-        input.locationCode === DEFAULT_LOCATION_CODE
-          ? ""
-          : ` ${LOCATIONS[input.locationCode] ?? input.locationCode}`;
-      return `${input.domain}${locationSuffix}`;
-    }, []),
+    getLabel: useCallback(
+      (input) => {
+        if (input.type !== "domain") return "";
+        const locationSuffix =
+          input.locationCode == null ||
+          input.locationCode === routeState.defaultLocationCode
+            ? ""
+            : ` ${LOCATIONS[input.locationCode] ?? input.locationCode}`;
+        return `${input.domain}${locationSuffix}`;
+      },
+      [routeState.defaultLocationCode],
+    ),
     navigateToInput: navigateToSearchTab,
   });
 
@@ -623,7 +636,6 @@ export function DomainOverviewPage({
                   key="keywords"
                   projectId={projectId}
                   domain={state.overview.domain}
-                  languageCode={state.languageCode}
                   routeState={routeState}
                   canSaveKeywords={state.canSaveKeywords}
                   setSearchParams={state.setSearchParams}
@@ -636,7 +648,6 @@ export function DomainOverviewPage({
                   key="pages"
                   projectId={projectId}
                   domain={state.overview.domain}
-                  languageCode={state.languageCode}
                   routeState={routeState}
                   setSearchParams={state.setSearchParams}
                   onSortClick={state.handleSortColumnClick}
diff --git a/src/client/features/domain/components/KeywordsTab.tsx b/src/client/features/domain/components/KeywordsTab.tsx
index 36702ba..2b76bcf 100644
--- a/src/client/features/domain/components/KeywordsTab.tsx
+++ b/src/client/features/domain/components/KeywordsTab.tsx
@@ -65,7 +65,6 @@ const KEYWORD_RANGE_FILTERS = [
 type Props = {
   projectId: string;
   domain: string;
-  languageCode: string;
   routeState: DomainOverviewRouteState;
   canSaveKeywords: boolean;
   setSearchParams: (updates: SearchUpdate) => void;
@@ -77,7 +76,6 @@ type Props = {
 export function KeywordsTab({
   projectId,
   domain,
-  languageCode,
   routeState,
   canSaveKeywords,
   setSearchParams,
@@ -106,8 +104,7 @@ export function KeywordsTab({
     projectId,
     domain,
     includeSubdomains: routeState.subdomains,
-    locationCode: routeState.locationCode,
-    languageCode,
+    locationCode: routeState.sentLocationCode,
     page: routeState.page,
     pageSize: routeState.pageSize,
     sortMode: routeState.sort,
@@ -159,13 +156,11 @@ export function KeywordsTab({
       filteredKeywords: rows,
       save: saveMutation.mutate,
       projectId,
-      locationCode: routeState.locationCode,
-      languageCode,
+      locationCode: routeState.sentLocationCode,
     });
   }, [
-    languageCode,
     projectId,
-    routeState.locationCode,
+    routeState.sentLocationCode,
     rows,
     saveMutation.mutate,
     selectedKeywords,
diff --git a/src/client/features/domain/components/PagesTab.tsx b/src/client/features/domain/components/PagesTab.tsx
index 88dc522..cd1b8a1 100644
--- a/src/client/features/domain/components/PagesTab.tsx
+++ b/src/client/features/domain/components/PagesTab.tsx
@@ -55,7 +55,6 @@ const PAGE_RANGE_FILTERS = [
 type Props = {
   projectId: string;
   domain: string;
-  languageCode: string;
   routeState: DomainOverviewRouteState;
   setSearchParams: (updates: SearchUpdate) => void;
   onSortClick: (sort: DomainSortMode) => void;
@@ -66,7 +65,6 @@ type Props = {
 export function PagesTab({
   projectId,
   domain,
-  languageCode,
   routeState,
   setSearchParams,
   onSortClick,
@@ -98,8 +96,7 @@ export function PagesTab({
     projectId,
     domain,
     includeSubdomains: routeState.subdomains,
-    locationCode: routeState.locationCode,
-    languageCode,
+    locationCode: routeState.sentLocationCode,
     page: routeState.page,
     pageSize: routeState.pageSize,
     sortMode: routeState.sort,
diff --git a/src/client/features/domain/domainActions.ts b/src/client/features/domain/domainActions.ts
index c00f683..a3e00bf 100644
--- a/src/client/features/domain/domainActions.ts
+++ b/src/client/features/domain/domainActions.ts
@@ -6,8 +6,7 @@ import type { KeywordRow } from "@/client/features/domain/types";
 type SaveMutation = (payload: {
   projectId: string;
   keywords: string[];
-  locationCode: number;
-  languageCode: string;
+  locationCode?: number;
   metrics?: Array<{
     keyword: string;
     searchVolume?: number | null;
@@ -27,14 +26,12 @@ export function saveSelectedKeywords({
   save,
   projectId,
   locationCode,
-  languageCode,
 }: {
   selectedKeywords: Set<string>;
   filteredKeywords: KeywordRow[];
   save: (payload: Parameters<SaveMutation>[0], opts?: SaveOptions) => void;
   projectId: string;
-  locationCode: number;
-  languageCode: string;
+  locationCode?: number;
 }) {
   if (selectedKeywords.size === 0) {
     toast.error("Select at least one keyword first");
@@ -49,7 +46,6 @@ export function saveSelectedKeywords({
       projectId,
       keywords: [...selectedKeywords],
       locationCode,
-      languageCode,
       metrics: selectedRows.map((row) => ({
         keyword: row.keyword,
         searchVolume: row.searchVolume,
diff --git a/src/client/features/domain/domainRouteState.test.ts b/src/client/features/domain/domainRouteState.test.ts
new file mode 100644
index 0000000..726a427
--- /dev/null
+++ b/src/client/features/domain/domainRouteState.test.ts
@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest";
+import { getDomainRouteState } from "./domainRouteState";
+
+describe("getDomainRouteState", () => {
+  it("uses a Labs-backed project market when the URL omits loc", () => {
+    const state = getDomainRouteState(
+      {},
+      { locationCode: 2704, languageCode: "vi" },
+    );
+
+    expect(state.defaultLocationCode).toBe(2704);
+    expect(state.locationCode).toBe(2704);
+    expect(state.sentLocationCode).toBeUndefined();
+  });
+
+  it("keeps an explicit Labs-backed URL location", () => {
+    const state = getDomainRouteState(
+      { loc: 2840 },
+      { locationCode: 2704, languageCode: "vi" },
+    );
+
+    expect(state.defaultLocationCode).toBe(2704);
+    expect(state.locationCode).toBe(2840);
+    expect(state.sentLocationCode).toBe(2840);
+  });
+
+  it("falls back to US for a Google-Ads-only project market", () => {
+    const state = getDomainRouteState(
+      {},
+      { locationCode: 2352, languageCode: "is" },
+    );
+
+    expect(state.defaultLocationCode).toBe(2840);
+    expect(state.locationCode).toBe(2840);
+    expect(state.sentLocationCode).toBeUndefined();
+  });
+
+  it("ignores a Google-Ads-only URL location", () => {
+    const state = getDomainRouteState(
+      { loc: 2352 },
+      { locationCode: 2704, languageCode: "vi" },
+    );
+
+    expect(state.defaultLocationCode).toBe(2704);
+    expect(state.locationCode).toBe(2704);
+    expect(state.sentLocationCode).toBe(2352);
+  });
+});
diff --git a/src/client/features/domain/domainRouteState.ts b/src/client/features/domain/domainRouteState.ts
index b243fbb..8180389 100644
--- a/src/client/features/domain/domainRouteState.ts
+++ b/src/client/features/domain/domainRouteState.ts
@@ -6,6 +6,7 @@ import {
   DEFAULT_LOCATION_CODE,
   isLabsLocationCode,
 } from "@/client/features/keywords/locations";
+import type { ProjectMarket } from "@/client/features/projects/types";
 import {
   EMPTY_DOMAIN_FILTERS,
   type DomainActiveTab,
@@ -28,7 +29,9 @@ export type DomainOverviewRouteState = {
   sort: DomainSortMode;
   order: SortOrder;
   tab: DomainActiveTab;
+  defaultLocationCode: number;
   locationCode: number;
+  sentLocationCode: number | undefined;
   page: number;
   pageSize: number;
   appliedFilters: DomainFilterValues;
@@ -44,13 +47,18 @@ function numberToFilterString(value: number | undefined): string {
 
 export function getDomainRouteState(
   search: DomainSearchParams,
+  projectMarket?: ProjectMarket,
 ): DomainOverviewRouteState {
   const normalizedSort = toSortMode(search.sort ?? null) ?? "traffic";
+  const defaultLocationCode =
+    projectMarket && isLabsLocationCode(projectMarket.locationCode)
+      ? projectMarket.locationCode
+      : DEFAULT_LOCATION_CODE;
   // Domain analytics is Labs-backed; Google-Ads-only countries aren't valid.
   const normalizedLocationCode =
     search.loc != null && isLabsLocationCode(search.loc)
       ? search.loc
-      : DEFAULT_LOCATION_CODE;
+      : defaultLocationCode;
 
   return {
     domain: search.domain ?? "",
@@ -58,7 +66,9 @@ export function getDomainRouteState(
     sort: normalizedSort,
     order: resolveSortOrder(normalizedSort, toSortOrder(search.order ?? null)),
     tab: search.tab ?? "keywords",
+    defaultLocationCode,
     locationCode: normalizedLocationCode,
+    sentLocationCode: search.loc,
     page: search.page != null && search.page > 0 ? search.page : 1,
     pageSize: search.size ?? DEFAULT_DOMAIN_KEYWORDS_PAGE_SIZE,
     appliedFilters: {
diff --git a/src/client/features/domain/hooks/useDomainKeywordsQuery.ts b/src/client/features/domain/hooks/useDomainKeywordsQuery.ts
index 3c2699c..1e69efb 100644
--- a/src/client/features/domain/hooks/useDomainKeywordsQuery.ts
+++ b/src/client/features/domain/hooks/useDomainKeywordsQuery.ts
@@ -12,8 +12,7 @@ type DomainKeywordsQueryInput = {
   projectId: string;
   domain: string;
   includeSubdomains: boolean;
-  locationCode: number;
-  languageCode: string;
+  locationCode: number | undefined;
   page: number;
   pageSize: number;
   sortMode: DomainSortMode;
@@ -60,7 +59,6 @@ export function useDomainKeywordsQuery(input: DomainKeywordsQueryInput) {
       input.domain,
       input.includeSubdomains,
       input.locationCode,
-      input.languageCode,
       input.page,
       input.pageSize,
       input.sortMode,
@@ -71,7 +69,6 @@ export function useDomainKeywordsQuery(input: DomainKeywordsQueryInput) {
       filtersPayload,
       input.domain,
       input.includeSubdomains,
-      input.languageCode,
       input.locationCode,
       input.page,
       input.pageSize,
@@ -98,7 +95,6 @@ export function useDomainKeywordsQuery(input: DomainKeywordsQueryInput) {
           domain: input.domain,
           includeSubdomains: input.includeSubdomains,
           locationCode: input.locationCode,
-          languageCode: input.languageCode,
           page: input.page,
           pageSize: input.pageSize,
           sortMode: input.sortMode,
diff --git a/src/client/features/domain/hooks/useDomainOverviewQuery.ts b/src/client/features/domain/hooks/useDomainOverviewQuery.ts
index 28a7abe..a6cea65 100644
--- a/src/client/features/domain/hooks/useDomainOverviewQuery.ts
+++ b/src/client/features/domain/hooks/useDomainOverviewQuery.ts
@@ -5,8 +5,7 @@ type Input = {
   projectId: string;
   domain: string;
   includeSubdomains: boolean;
-  locationCode: number;
-  languageCode: string;
+  locationCode: number | undefined;
 };
 
 export function useDomainOverviewQuery(input: Input) {
@@ -20,7 +19,6 @@ export function useDomainOverviewQuery(input: Input) {
       trimmedDomain,
       input.includeSubdomains,
       input.locationCode,
-      input.languageCode,
     ],
     queryFn: () =>
       getDomainOverview({
@@ -29,7 +27,6 @@ export function useDomainOverviewQuery(input: Input) {
           domain: trimmedDomain,
           includeSubdomains: input.includeSubdomains,
           locationCode: input.locationCode,
-          languageCode: input.languageCode,
         },
       }),
     staleTime: 5 * 60_000,
diff --git a/src/client/features/domain/hooks/useDomainPagesQuery.ts b/src/client/features/domain/hooks/useDomainPagesQuery.ts
index fe11694..28a433c 100644
--- a/src/client/features/domain/hooks/useDomainPagesQuery.ts
+++ b/src/client/features/domain/hooks/useDomainPagesQuery.ts
@@ -13,8 +13,7 @@ type DomainPagesQueryInput = {
   projectId: string;
   domain: string;
   includeSubdomains: boolean;
-  locationCode: number;
-  languageCode: string;
+  locationCode: number | undefined;
   page: number;
   pageSize: number;
   sortMode: DomainSortMode;
@@ -32,7 +31,6 @@ export function useDomainPagesQuery(input: DomainPagesQueryInput) {
       input.domain,
       input.includeSubdomains,
       input.locationCode,
-      input.languageCode,
       input.page,
       input.pageSize,
       pageSortMode,
@@ -43,7 +41,6 @@ export function useDomainPagesQuery(input: DomainPagesQueryInput) {
       input.appliedFilters,
       input.domain,
       input.includeSubdomains,
-      input.languageCode,
       input.locationCode,
       input.page,
       input.pageSize,
@@ -70,7 +67,6 @@ export function useDomainPagesQuery(input: DomainPagesQueryInput) {
           domain: input.domain,
           includeSubdomains: input.includeSubdomains,
           locationCode: input.locationCode,
-          languageCode: input.languageCode,
           page: input.page,
           pageSize: input.pageSize,
           sortMode: pageSortMode,
diff --git a/src/client/features/domain/mutations.ts b/src/client/features/domain/mutations.ts
index 3ad740e..6d7ae4f 100644
--- a/src/client/features/domain/mutations.ts
+++ b/src/client/features/domain/mutations.ts
@@ -12,8 +12,7 @@ export function useSaveKeywordsMutation({
     mutationFn: (data: {
       projectId: string;
       keywords: string[];
-      locationCode: number;
-      languageCode: string;
+      locationCode?: number;
       metrics?: Array<{
         keyword: string;
         searchVolume?: number | null;
diff --git a/src/client/features/keywords/hooks/useKeywordControlsForm.ts b/src/client/features/keywords/hooks/useKeywordControlsForm.ts
index b9b19b9..92d381a 100644
--- a/src/client/features/keywords/hooks/useKeywordControlsForm.ts
+++ b/src/client/features/keywords/hooks/useKeywordControlsForm.ts
@@ -13,7 +13,7 @@ import { parseKeywordInput } from "@/client/features/keywords/state/keywordContr
 
 type KeywordTabValidationInput = {
   keyword: string;
-  locationCode: number;
+  locationCode: number | undefined;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
diff --git a/src/client/features/keywords/hooks/useKeywordResearchData.test.ts b/src/client/features/keywords/hooks/useKeywordResearchData.test.ts
new file mode 100644
index 0000000..7e414cb
--- /dev/null
+++ b/src/client/features/keywords/hooks/useKeywordResearchData.test.ts
@@ -0,0 +1,35 @@
+import { describe, expect, it, vi } from "vitest";
+
+// The hook module pulls in the server functions it calls, whose graph reaches
+// Workers-only bindings that don't resolve outside workerd.
+vi.mock("cloudflare:workers", () => ({ env: {} }));
+
+import { buildKeywordResearchRequest } from "./useKeywordResearchData";
+
+const baseInput = {
+  projectId: "project_1",
+  keywordInput: "technical seo",
+  locationCode: 2704,
+  resultLimit: 150 as const,
+  mode: "auto" as const,
+  clickstream: false,
+};
+
+describe("buildKeywordResearchRequest", () => {
+  it("carries an explicitly selected location without a language", () => {
+    const request = buildKeywordResearchRequest(baseInput);
+
+    expect(request).toMatchObject({ locationCode: 2704 });
+    expect(request).not.toHaveProperty("languageCode");
+  });
+
+  it("leaves the location undefined for the server to resolve", () => {
+    const request = buildKeywordResearchRequest({
+      ...baseInput,
+      locationCode: undefined,
+    });
+
+    expect(request).toMatchObject({ locationCode: undefined });
+    expect(request).not.toHaveProperty("languageCode");
+  });
+});
diff --git a/src/client/features/keywords/hooks/useKeywordResearchData.ts b/src/client/features/keywords/hooks/useKeywordResearchData.ts
index a2a08e7..f93083b 100644
--- a/src/client/features/keywords/hooks/useKeywordResearchData.ts
+++ b/src/client/features/keywords/hooks/useKeywordResearchData.ts
@@ -2,8 +2,7 @@ import { useEffect, useMemo, useRef } from "react";
 import { useQuery } from "@tanstack/react-query";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
 import { captureClientEvent } from "@/client/lib/posthog";
-import { LOCATIONS, getLanguageCode } from "@/client/features/keywords/utils";
-import { DEFAULT_LOCATION_CODE } from "@/client/features/keywords/locations";
+import { LOCATIONS } from "@/client/features/keywords/utils";
 import { parseKeywordInput } from "@/client/features/keywords/state/keywordControllerActions";
 import { researchKeywords } from "@/serverFunctions/keywords";
 import type {
@@ -18,21 +17,24 @@ type AddSearchFn = (
   locationName: string,
 ) => void;
 
-type KeywordResearchQueryInput = {
+type KeywordResearchRequestInput = {
   projectId: string;
   keywordInput: string;
-  locationCode: number;
+  locationCode: number | undefined;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
 };
 
+type KeywordResearchQueryInput = KeywordResearchRequestInput & {
+  displayedLocationCode: number;
+};
+
 type KeywordResearchRequest = {
   projectId: string;
   keywords: string[];
   seedKeyword: string;
-  locationCode: number;
-  languageCode: string;
+  locationCode: number | undefined;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
@@ -41,7 +43,7 @@ type KeywordResearchRequest = {
 export const KEYWORD_RESEARCH_STALE_TIME_MS = 24 * 60 * 60 * 1000;
 
 export function buildKeywordResearchRequest(
-  input: KeywordResearchQueryInput,
+  input: KeywordResearchRequestInput,
 ): KeywordResearchRequest | null {
   const keywords = parseKeywordInput(input.keywordInput);
   const seedKeyword = keywords[0] ?? "";
@@ -52,7 +54,6 @@ export function buildKeywordResearchRequest(
     keywords,
     seedKeyword,
     locationCode: input.locationCode,
-    languageCode: getLanguageCode(input.locationCode),
     resultLimit: input.resultLimit,
     mode: input.mode,
     clickstream: input.clickstream,
@@ -68,7 +69,6 @@ export function buildKeywordResearchQueryKey(
         request.projectId,
         request.keywords,
         request.locationCode,
-        request.languageCode,
         request.resultLimit,
         request.mode,
         request.clickstream,
@@ -82,7 +82,6 @@ export function keywordResearchQueryFn(request: KeywordResearchRequest) {
       projectId: request.projectId,
       keywords: request.keywords,
       locationCode: request.locationCode,
-      languageCode: request.languageCode,
       resultLimit: request.resultLimit,
       mode: request.mode,
       clickstream: request.clickstream,
@@ -96,6 +95,7 @@ export function useKeywordResearchData(
 ) {
   const {
     clickstream,
+    displayedLocationCode,
     keywordInput,
     locationCode,
     mode,
@@ -144,7 +144,7 @@ export function useKeywordResearchData(
     handledSuccessKeyRef.current = queryKeyString;
 
     captureClientEvent("keyword_research:search_complete", {
-      location_code: request.locationCode,
+      location_code: displayedLocationCode,
       search_mode: request.mode,
       clickstream: request.clickstream,
       result_count: researchQuery.data.rows.length,
@@ -152,18 +152,19 @@ export function useKeywordResearchData(
 
     addSearch(
       request.seedKeyword,
-      request.locationCode,
-      LOCATIONS[request.locationCode] || "Unknown",
+      displayedLocationCode,
+      LOCATIONS[displayedLocationCode] || "Unknown",
     );
   }, [
     addSearch,
+    displayedLocationCode,
     queryKeyString,
     request,
     researchQuery.data,
     researchQuery.isSuccess,
   ]);
 
-  const hasSearched = request !== null;
+  const hasSearched = parseKeywordInput(keywordInput).length > 0;
   const rows = hasSearched ? (researchQuery.data?.rows ?? []) : [];
   const researchError =
     hasSearched && researchQuery.isError
@@ -178,7 +179,7 @@ export function useKeywordResearchData(
       researchQuery.data?.source ?? ("related" as ResearchSource),
     lastUsedFallback: researchQuery.data?.usedFallback ?? false,
     lastSearchKeyword: request?.seedKeyword ?? "",
-    lastSearchLocationCode: request?.locationCode ?? DEFAULT_LOCATION_CODE,
+    lastSearchLocationCode: displayedLocationCode,
     researchError,
     researchMutationError: researchQuery.error,
     searchedKeyword: request?.seedKeyword ?? "",
diff --git a/src/client/features/keywords/hooks/useKeywordSerpAnalysis.ts b/src/client/features/keywords/hooks/useKeywordSerpAnalysis.ts
index 016fdfc..6f01ce1 100644
--- a/src/client/features/keywords/hooks/useKeywordSerpAnalysis.ts
+++ b/src/client/features/keywords/hooks/useKeywordSerpAnalysis.ts
@@ -1,12 +1,11 @@
 import { useQuery } from "@tanstack/react-query";
 import { useState } from "react";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
-import { getLanguageCode } from "@/client/features/keywords/utils";
 import { getSerpAnalysis } from "@/serverFunctions/keywords";
 
 export function useKeywordSerpAnalysis(
   projectId: string,
-  locationCode: number,
+  locationCode: number | undefined,
 ) {
   const [serpKeyword, setSerpKeyword] = useState<string | null>(null);
   const [serpPage, setSerpPage] = useState(0);
@@ -20,7 +19,6 @@ export function useKeywordSerpAnalysis(
           projectId,
           keyword: serpKeyword!,
           locationCode,
-          languageCode: getLanguageCode(locationCode),
         },
       }),
     enabled: !!serpKeyword,
@@ -29,7 +27,7 @@ export function useKeywordSerpAnalysis(
   const serpResults = serpQuery.data?.items ?? [];
   const activeSerpKeyword =
     serpKeyword ?? serpQuery.data?.requestedKeyword ?? null;
-  const serpLoading = serpQuery.isLoading;
+  const serpLoading = !!serpKeyword && serpQuery.isLoading;
   const serpError = serpQuery.isError
     ? getStandardErrorMessage(serpQuery.error, "Failed to load SERP data.")
     : null;
diff --git a/src/client/features/keywords/hooks/usePreferredKeywordLocation.ts b/src/client/features/keywords/hooks/usePreferredKeywordLocation.ts
index a27dcd4..0e84c9f 100644
--- a/src/client/features/keywords/hooks/usePreferredKeywordLocation.ts
+++ b/src/client/features/keywords/hooks/usePreferredKeywordLocation.ts
@@ -5,12 +5,15 @@ import {
   isSupportedLocationCode,
 } from "@/client/features/keywords/locations";
 
-const STORAGE_KEY = "keyword-preferred-location";
+// Scoped per project: a location picked while working on one project must not
+// shadow another project's own default market.
+const storageKey = (projectId: string) =>
+  `keyword-preferred-location:${projectId}`;
 const locationCodeSchema = z.number().int().positive();
 
-function loadPreferredLocationCode() {
+function loadPreferredLocationCode(projectId: string) {
   try {
-    const raw = localStorage.getItem(STORAGE_KEY);
+    const raw = localStorage.getItem(storageKey(projectId));
     if (!raw) return null;
 
     const parsed = locationCodeSchema.parse(JSON.parse(raw));
@@ -20,31 +23,49 @@ function loadPreferredLocationCode() {
   }
 }
 
-function savePreferredLocationCode(locationCode: number) {
+function savePreferredLocationCode(projectId: string, locationCode: number) {
   try {
-    localStorage.setItem(STORAGE_KEY, JSON.stringify(locationCode));
+    localStorage.setItem(storageKey(projectId), JSON.stringify(locationCode));
   } catch {
     // storage full or unavailable - silently ignore
   }
 }
 
-export function usePreferredKeywordLocation() {
-  const [preferredLocationCode, setPreferredLocationCodeState] = useState(
-    DEFAULT_LOCATION_CODE,
-  );
+/**
+ * Preference order: the user's explicit choice for this project (persisted per
+ * browser) > the project's default market (may arrive async from the projects
+ * query) > the US fallback.
+ */
+export function usePreferredKeywordLocation(
+  projectId: string,
+  projectDefaultLocationCode?: number,
+) {
+  const [preference, setPreference] = useState(() => ({
+    projectId,
+    locationCode: loadPreferredLocationCode(projectId),
+  }));
+  const chosenLocationCode =
+    preference.projectId === projectId
+      ? preference.locationCode
+      : loadPreferredLocationCode(projectId);
 
   useEffect(() => {
-    const savedLocationCode = loadPreferredLocationCode();
-    if (savedLocationCode != null) {
-      setPreferredLocationCodeState(savedLocationCode);
-    }
-  }, []);
+    if (preference.projectId === projectId) return;
+    setPreference({ projectId, locationCode: chosenLocationCode });
+  }, [chosenLocationCode, preference.projectId, projectId]);
+
+  const preferredLocationCode =
+    chosenLocationCode ?? projectDefaultLocationCode ?? DEFAULT_LOCATION_CODE;
 
   function setPreferredLocationCode(locationCode: number) {
     if (!isSupportedLocationCode(locationCode)) return;
-    setPreferredLocationCodeState(locationCode);
-    savePreferredLocationCode(locationCode);
+    setPreference({ projectId, locationCode });
+    savePreferredLocationCode(projectId, locationCode);
   }
 
-  return { preferredLocationCode, setPreferredLocationCode };
+  return {
+    preferredLocationCode,
+    selectedLocationCode: chosenLocationCode ?? undefined,
+    setPreferredLocationCode,
+  };
 }
diff --git a/src/client/features/keywords/page/KeywordResearchEmptyState.tsx b/src/client/features/keywords/page/KeywordResearchEmptyState.tsx
index 7ffbfcb..1453289 100644
--- a/src/client/features/keywords/page/KeywordResearchEmptyState.tsx
+++ b/src/client/features/keywords/page/KeywordResearchEmptyState.tsx
@@ -1,6 +1,5 @@
 import { Link } from "@tanstack/react-router";
 import { Clock, Globe, History, Search, X } from "lucide-react";
-import { DEFAULT_LOCATION_CODE } from "@/client/features/keywords/locations";
 import { LOCATIONS } from "@/client/features/keywords/utils";
 import type { KeywordResearchControllerState } from "./types";
 
@@ -89,10 +88,7 @@ function SearchHistoryState({
                   params={{ projectId }}
                   search={{
                     q: item.keyword,
-                    loc:
-                      item.locationCode === DEFAULT_LOCATION_CODE
-                        ? undefined
-                        : item.locationCode,
+                    loc: item.locationCode,
                   }}
                   replace
                   className="flex min-w-0 flex-1 items-center gap-3 rounded-md px-1 py-1 text-left transition-colors hover:bg-base-200"
diff --git a/src/client/features/keywords/page/KeywordResearchPage.tsx b/src/client/features/keywords/page/KeywordResearchPage.tsx
index 8442fb5..a9ea173 100644
--- a/src/client/features/keywords/page/KeywordResearchPage.tsx
+++ b/src/client/features/keywords/page/KeywordResearchPage.tsx
@@ -7,21 +7,30 @@ import { useKeywordResearchController } from "@/client/features/keywords/state/u
 import type { KeywordResearchControllerInput } from "@/client/features/keywords/state/useKeywordResearchController";
 import type { KeywordControlsValues } from "@/client/features/keywords/hooks/useKeywordControlsForm";
 import { parseKeywordInput } from "@/client/features/keywords/state/keywordControllerActions";
-import { useKeywordSearchParams } from "@/client/features/keywords/state/keywordControllerInternals";
-import { DEFAULT_LOCATION_CODE } from "@/client/features/keywords/locations";
+import {
+  useKeywordSearchParams,
+  useResolvedKeywordLocation,
+} from "@/client/features/keywords/state/keywordControllerInternals";
 import type {
   KeywordSearchTabInput,
   SearchTab,
 } from "@/client/features/search-tabs/types";
 import { SearchTabStrip } from "@/client/features/search-tabs/SearchTabStrip";
-import { useSearchTabNavigation } from "@/client/features/search-tabs/useSearchTabNavigation";
+import {
+  tabInputKey,
+  useSearchTabNavigation,
+} from "@/client/features/search-tabs/useSearchTabNavigation";
 import { KeywordResearchEmptyState } from "./KeywordResearchEmptyState";
 import { KeywordResearchLoadingState } from "./KeywordResearchLoadingState";
 import { KeywordResearchResults } from "./KeywordResearchResults";
 import { KeywordResearchSearchBar } from "./KeywordResearchSearchBar";
 import type { KeywordResearchControllerState } from "./types";
 
-type Props = Omit<KeywordResearchControllerInput, "onFormSubmit">;
+type ControllerProps = Omit<KeywordResearchControllerInput, "onFormSubmit">;
+type Props = Omit<
+  ControllerProps,
+  "locationCode" | "displayedLocationCode" | "setPreferredLocationCode"
+> & { locationCode?: number };
 type KeywordSearchTab = SearchTab & { input: KeywordSearchTabInput };
 
 function isKeywordSearchTab(tab: SearchTab): tab is KeywordSearchTab {
@@ -31,6 +40,11 @@ function isKeywordSearchTab(tab: SearchTab): tab is KeywordSearchTab {
 export function KeywordResearchPage(input: Props) {
   const setSearchParams = useKeywordSearchParams();
   const projectId = input.projectId;
+  const { locationCode, displayedLocationCode, setPreferredLocationCode } =
+    useResolvedKeywordLocation({
+      projectId,
+      locationCode: input.locationCode,
+    });
 
   const navigateToKeywordInput = useCallback(
     (tabInput: KeywordSearchTabInput | null) => {
@@ -47,10 +61,7 @@ export function KeywordResearchPage(input: Props) {
 
       setSearchParams({
         q: tabInput.keyword,
-        loc:
-          tabInput.locationCode === DEFAULT_LOCATION_CODE
-            ? undefined
-            : tabInput.locationCode,
+        loc: tabInput.locationCode,
         kLimit: tabInput.resultLimit === 150 ? undefined : tabInput.resultLimit,
         mode: tabInput.mode === "auto" ? undefined : tabInput.mode,
         cs: tabInput.clickstream ? true : undefined,
@@ -66,7 +77,7 @@ export function KeywordResearchPage(input: Props) {
     return {
       type: "keyword",
       keyword,
-      locationCode: input.locationCode,
+      locationCode,
       resultLimit: input.resultLimit,
       mode: input.keywordMode,
       clickstream: input.clickstream,
@@ -75,7 +86,7 @@ export function KeywordResearchPage(input: Props) {
     input.clickstream,
     input.keywordInput,
     input.keywordMode,
-    input.locationCode,
+    locationCode,
     input.resultLimit,
   ]);
   const searchTabs = useSearchTabNavigation({
@@ -98,7 +109,13 @@ export function KeywordResearchPage(input: Props) {
     const tab = searchTabs.tabs.find(
       (candidate) => candidate.id === searchTabs.activeTabId,
     );
-    return tab && isKeywordSearchTab(tab) ? tab : null;
+    // activeTabId syncs in an effect, so it trails urlInput by a render; the
+    // stale tab must not drive a paid query for a market the URL no longer names.
+    return tab &&
+      isKeywordSearchTab(tab) &&
+      tabInputKey(tab.input) === tabInputKey(urlInput)
+      ? tab
+      : null;
   }, [searchTabs.activeTabId, searchTabs.tabs, urlInput]);
 
   const onFormSubmit = useCallback(
@@ -148,14 +165,16 @@ export function KeywordResearchPage(input: Props) {
     [searchTabs.tabs],
   );
 
-  const controllerInput = useMemo<Props>(
+  const controllerInput = useMemo<ControllerProps>(
     () =>
       activeTab
         ? {
             ...input,
             keywordInput: activeTab.input.keyword,
             locationCode: activeTab.input.locationCode,
-            hasExplicitLocationCode: true,
+            displayedLocationCode:
+              activeTab.input.locationCode ?? displayedLocationCode,
+            setPreferredLocationCode,
             resultLimit: activeTab.input.resultLimit,
             keywordMode: activeTab.input.mode,
             clickstream: activeTab.input.clickstream,
@@ -164,10 +183,21 @@ export function KeywordResearchPage(input: Props) {
           }
         : {
             ...input,
+            locationCode,
+            displayedLocationCode,
+            setPreferredLocationCode,
             getOpenKeywordTabs,
             keywordTabsLimit: searchTabs.limit,
           },
-    [activeTab, getOpenKeywordTabs, input, searchTabs.limit],
+    [
+      activeTab,
+      getOpenKeywordTabs,
+      input,
+      displayedLocationCode,
+      locationCode,
+      searchTabs.limit,
+      setPreferredLocationCode,
+    ],
   );
   const controller = useKeywordResearchController({
     ...controllerInput,
diff --git a/src/client/features/keywords/state/keywordControllerActions.ts b/src/client/features/keywords/state/keywordControllerActions.ts
index 192a2a5..f11c668 100644
--- a/src/client/features/keywords/state/keywordControllerActions.ts
+++ b/src/client/features/keywords/state/keywordControllerActions.ts
@@ -3,7 +3,6 @@ import { toast } from "sonner";
 import { buildCsv, type CsvValue, downloadCsv } from "@/client/lib/csv";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
 import { captureClientEvent } from "@/client/lib/posthog";
-import { getLanguageCode } from "@/client/features/keywords/utils";
 import type { KeywordResearchRow } from "@/types/keywords";
 import type { SaveKeywordsInput } from "@/types/schemas/keywords";
 import type { SortDir, SortField } from "@/client/features/keywords/components";
@@ -62,7 +61,7 @@ export function parseKeywordInput(value: string) {
  */
 export function buildKeywordSearchKey(params: {
   keyword: string;
-  locationCode: number;
+  locationCode: number | undefined;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
@@ -127,7 +126,6 @@ export function useSaveAndExportActions(params: SaveExportActionParams) {
         projectId: input.projectId,
         keywords: [...selectedRows],
         locationCode: input.locationCode,
-        languageCode: getLanguageCode(input.locationCode),
         metrics,
       },
       {
diff --git a/src/client/features/keywords/state/keywordControllerInternals.ts b/src/client/features/keywords/state/keywordControllerInternals.ts
index 13e59d6..affbd45 100644
--- a/src/client/features/keywords/state/keywordControllerInternals.ts
+++ b/src/client/features/keywords/state/keywordControllerInternals.ts
@@ -2,22 +2,25 @@ import { useNavigate } from "@tanstack/react-router";
 import { useMutation, useQueryClient } from "@tanstack/react-query";
 import { useCallback, useState } from "react";
 import { usePreferredKeywordLocation } from "@/client/features/keywords/hooks/usePreferredKeywordLocation";
+import { useProjectMarket } from "@/client/features/projects/useProjectMarket";
 import { saveKeywords } from "@/serverFunctions/keywords";
 import type { SaveKeywordsInput } from "@/types/schemas/keywords";
 import type { KeywordResearchRow } from "@/types/keywords";
-import type { KeywordResearchControllerInput } from "./useKeywordResearchController";
 
-export function useResolvedKeywordLocation(
-  input: KeywordResearchControllerInput,
-) {
-  const { preferredLocationCode, setPreferredLocationCode } =
-    usePreferredKeywordLocation();
-  const locationCode =
-    !input.hasExplicitLocationCode && input.keywordInput === ""
-      ? preferredLocationCode
-      : input.locationCode;
+export function useResolvedKeywordLocation(input: {
+  projectId: string;
+  locationCode?: number;
+}) {
+  const projectMarket = useProjectMarket(input.projectId);
+  const {
+    preferredLocationCode,
+    selectedLocationCode,
+    setPreferredLocationCode,
+  } = usePreferredKeywordLocation(input.projectId, projectMarket?.locationCode);
+  const locationCode = input.locationCode ?? selectedLocationCode;
+  const displayedLocationCode = input.locationCode ?? preferredLocationCode;
 
-  return { locationCode, setPreferredLocationCode };
+  return { locationCode, displayedLocationCode, setPreferredLocationCode };
 }
 
 export function useKeywordUiState(initialShowFilters: boolean) {
diff --git a/src/client/features/keywords/state/useKeywordResearchController.ts b/src/client/features/keywords/state/useKeywordResearchController.ts
index 3cbc1e8..9fed9c1 100644
--- a/src/client/features/keywords/state/useKeywordResearchController.ts
+++ b/src/client/features/keywords/state/useKeywordResearchController.ts
@@ -25,13 +25,12 @@ import {
   useKeywordSaveMutation,
   useKeywordSearchParams,
   useKeywordUiState,
-  useResolvedKeywordLocation,
 } from "./keywordControllerInternals";
 import { useKeywordOverviewState } from "./useKeywordOverviewState";
 
 type OpenKeywordTabInput = {
   keyword: string;
-  locationCode: number;
+  locationCode: number | undefined;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
@@ -40,8 +39,9 @@ type OpenKeywordTabInput = {
 export type KeywordResearchControllerInput = {
   projectId: string;
   keywordInput: string;
-  locationCode: number;
-  hasExplicitLocationCode: boolean;
+  locationCode: number | undefined;
+  displayedLocationCode: number;
+  setPreferredLocationCode: (locationCode: number) => void;
   resultLimit: ResultLimit;
   keywordMode: KeywordMode;
   clickstream: boolean;
@@ -60,8 +60,8 @@ export type KeywordResearchControllerInput = {
 export function useKeywordResearchController(
   input: KeywordResearchControllerInput,
 ) {
-  const { locationCode, setPreferredLocationCode } =
-    useResolvedKeywordLocation(input);
+  const { displayedLocationCode, locationCode, setPreferredLocationCode } =
+    input;
   const {
     filtersForm,
     values: filterValues,
@@ -115,6 +115,7 @@ export function useKeywordResearchController(
       projectId: input.projectId,
       keywordInput: input.keywordInput,
       locationCode,
+      displayedLocationCode,
       resultLimit: input.resultLimit,
       mode: input.keywordMode,
       clickstream: input.clickstream,
@@ -148,7 +149,7 @@ export function useKeywordResearchController(
   const controlsForm = useKeywordControlsForm(
     {
       ...input,
-      locationCode,
+      locationCode: displayedLocationCode,
       getOpenKeywordTabs: input.getOpenKeywordTabs,
       keywordTabsLimit: input.keywordTabsLimit,
     },
diff --git a/src/client/features/keywords/utils.ts b/src/client/features/keywords/utils.ts
index 4bb6448..696d14b 100644
--- a/src/client/features/keywords/utils.ts
+++ b/src/client/features/keywords/utils.ts
@@ -1,4 +1,4 @@
-export { LOCATIONS, getLanguageCode } from "./locations";
+export { LOCATIONS } from "./locations";
 
 export function scoreTierClass(value: number | null): string {
   if (value == null) return "score-tier-na";
diff --git a/src/client/features/onboarding/SearchConsoleOnboardingStep.tsx b/src/client/features/onboarding/SearchConsoleOnboardingStep.tsx
index e1b5151..6205cb0 100644
--- a/src/client/features/onboarding/SearchConsoleOnboardingStep.tsx
+++ b/src/client/features/onboarding/SearchConsoleOnboardingStep.tsx
@@ -11,12 +11,14 @@ import {
 import { startGscLink } from "@/client/features/gsc/startGscLink";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
 import { captureClientEvent } from "@/client/lib/posthog";
+import { ProjectMarketFields } from "@/client/features/projects/ProjectMarketFields";
+import type { ProjectMarket } from "@/client/features/projects/types";
 import {
   getGscConnection,
   listGscSites,
   setGscSite,
 } from "@/serverFunctions/gsc";
-import { getProjects } from "@/serverFunctions/projects";
+import { getProjects, setProjectMarket } from "@/serverFunctions/projects";
 
 const GRANT_STATUS_KEY = ["gscGrantStatus"];
 
@@ -31,19 +33,66 @@ export function SearchConsoleOnboardingStep() {
     queryKey: ["projects"],
     queryFn: () => getProjects(),
   });
-  const projectId = projectsQuery.data?.[0]?.id;
+  const project = projectsQuery.data?.[0];
 
   return (
-    <div className="space-y-4">
-      <h2 className="text-lg font-semibold">
-        Connect with Google Search Console now?
-      </h2>
+    <div className="space-y-8">
+      <div className="space-y-4">
+        <h2 className="text-lg font-semibold">
+          Connect with Google Search Console now?
+        </h2>
 
-      {projectId ? <GscConnect projectId={projectId} /> : <Checking />}
+        {project ? <GscConnect projectId={project.id} /> : <Checking />}
 
+        <p className="text-xs leading-relaxed text-base-content/55">
+          For now, Search Console data flows through the OpenSEO MCP. We're
+          building it into the OpenSEO app soon too.
+        </p>
+      </div>
+
+      <div className="space-y-4">
+        <h2 className="text-lg font-semibold">Choose country &amp; language</h2>
+        {project ? <DefaultMarketPicker project={project} /> : <Checking />}
+      </div>
+    </div>
+  );
+}
+
+/**
+ * Sets the project's default market during onboarding, so keyword, SERP, and
+ * domain data lands on the user's market from their first search instead of
+ * defaulting to the US. Saves on change — the step's Continue button belongs
+ * to the wizard, so a separate Save here would be easy to walk past.
+ */
+function DefaultMarketPicker({
+  project,
+}: {
+  project: { id: string; locationCode: number; languageCode: string };
+}) {
+  const queryClient = useQueryClient();
+  const [market, setMarket] = React.useState<ProjectMarket>({
+    locationCode: project.locationCode,
+    languageCode: project.languageCode,
+  });
+
+  const saveMutation = useMutation({
+    mutationFn: (next: ProjectMarket) =>
+      setProjectMarket({ data: { projectId: project.id, ...next } }),
+    onSuccess: () => queryClient.invalidateQueries({ queryKey: ["projects"] }),
+    onError: (error) => toast.error(getStandardErrorMessage(error)),
+  });
+
+  const handleChange = (next: ProjectMarket) => {
+    setMarket(next);
+    saveMutation.mutate(next);
+  };
+
+  return (
+    <div className="space-y-2">
+      <ProjectMarketFields value={market} onChange={handleChange} />
       <p className="text-xs leading-relaxed text-base-content/55">
-        For now, Search Console data flows through the OpenSEO MCP. We're
-        building it into the OpenSEO app soon too.
+        We'll use this country and language for keyword, SERP, and domain data
+        unless you pick a different one. You can change it in project settings.
       </p>
     </div>
   );
diff --git a/src/client/features/projects/CreateProjectModal.tsx b/src/client/features/projects/CreateProjectModal.tsx
index 23f248e..0f1f1e5 100644
--- a/src/client/features/projects/CreateProjectModal.tsx
+++ b/src/client/features/projects/CreateProjectModal.tsx
@@ -5,6 +5,11 @@ import { toast } from "sonner";
 import { Modal } from "@/client/components/Modal";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
 import { setLastProjectId } from "@/client/lib/active-project";
+import {
+  DEFAULT_LOCATION_CODE,
+  getLanguageCode,
+} from "@/client/features/keywords/locations";
+import { ProjectMarketFields } from "@/client/features/projects/ProjectMarketFields";
 import { createProject } from "@/serverFunctions/projects";
 
 export function CreateProjectModal({ onClose }: { onClose: () => void }) {
@@ -12,11 +17,19 @@ export function CreateProjectModal({ onClose }: { onClose: () => void }) {
   const queryClient = useQueryClient();
   const [name, setName] = React.useState("");
   const [domain, setDomain] = React.useState("");
+  const [market, setMarket] = React.useState({
+    locationCode: DEFAULT_LOCATION_CODE,
+    languageCode: getLanguageCode(DEFAULT_LOCATION_CODE),
+  });
 
   const createMutation = useMutation({
     mutationFn: () =>
       createProject({
-        data: { name: name.trim(), domain: domain.trim() || undefined },
+        data: {
+          name: name.trim(),
+          domain: domain.trim() || undefined,
+          ...market,
+        },
       }),
     onSuccess: async (created) => {
       setLastProjectId(created.id);
@@ -88,6 +101,15 @@ export function CreateProjectModal({ onClose }: { onClose: () => void }) {
           </span>
         </label>
 
+        <div className="flex flex-col gap-1.5">
+          <ProjectMarketFields value={market} onChange={setMarket} />
+          <span className="text-xs text-base-content/50">
+            Keyword, SERP, and domain data uses this country and language unless
+            a call asks for a different one. Change it later in project
+            settings.
+          </span>
+        </div>
+
         <div className="flex justify-end gap-2">
           <button
             type="button"
diff --git a/src/client/features/projects/ProjectMarketFields.tsx b/src/client/features/projects/ProjectMarketFields.tsx
new file mode 100644
index 0000000..a82e386
--- /dev/null
+++ b/src/client/features/projects/ProjectMarketFields.tsx
@@ -0,0 +1,58 @@
+import { LocationSelect } from "@/client/components/LocationSelect";
+import {
+  getLanguageCode,
+  getLanguageOptions,
+} from "@/client/features/keywords/locations";
+import type { ProjectMarket } from "@/client/features/projects/types";
+
+/**
+ * The project's default market: country plus the language served for it.
+ * Shared by project settings and onboarding so the pair — and the rule that
+ * changing the country snaps the language to that country's native one —
+ * stays identical in both places.
+ */
+export function ProjectMarketFields({
+  value,
+  onChange,
+}: {
+  value: ProjectMarket;
+  onChange: (market: ProjectMarket) => void;
+}) {
+  const languageOptions = getLanguageOptions(value.locationCode);
+
+  return (
+    <div className="grid gap-4 sm:grid-cols-2">
+      <label className="flex flex-col gap-1.5 text-sm">
+        <span className="font-medium">Country</span>
+        <LocationSelect
+          value={value.locationCode}
+          onChange={(locationCode) =>
+            onChange({
+              locationCode,
+              languageCode: getLanguageCode(locationCode),
+            })
+          }
+        />
+      </label>
+      <label className="flex flex-col gap-1.5 text-sm">
+        <span className="font-medium">Language</span>
+        <select
+          value={value.languageCode}
+          onChange={(event) =>
+            onChange({ ...value, languageCode: event.target.value })
+          }
+          // Most countries have exactly one language DataForSEO serves, so the
+          // select is only a real choice where there's more than one.
+          disabled={languageOptions.length <= 1}
+          className="select select-bordered w-full"
+        >
+          {languageOptions.map((option) => (
+            <option key={option.code} value={option.code}>
+              {option.label}
+            </option>
+          ))}
+        </select>
+      </label>
+    </div>
+  );
+}
diff --git a/src/client/features/projects/ProjectSettings.tsx b/src/client/features/projects/ProjectSettings.tsx
index 63f1b3b..9d3026c 100644
--- a/src/client/features/projects/ProjectSettings.tsx
+++ b/src/client/features/projects/ProjectSettings.tsx
@@ -4,6 +4,7 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { ChevronLeft } from "lucide-react";
 import { toast } from "sonner";
 import { SearchConsoleConnectionCard } from "@/client/features/gsc/SearchConsoleConnectionCard";
+import { ProjectMarketFields } from "@/client/features/projects/ProjectMarketFields";
 import { getStandardErrorMessage } from "@/client/lib/error-messages";
 import {
   clearLastProjectId,
@@ -69,6 +70,10 @@ function GeneralSection({ project }: { project: ProjectSummary }) {
   const queryClient = useQueryClient();
   const [name, setName] = React.useState(project.name);
   const [domain, setDomain] = React.useState(project.domain ?? "");
+  const [market, setMarket] = React.useState({
+    locationCode: project.locationCode,
+    languageCode: project.languageCode,
+  });
 
   const updateMutation = useMutation({
     mutationFn: () =>
@@ -77,6 +82,7 @@ function GeneralSection({ project }: { project: ProjectSummary }) {
           projectId: project.id,
           name: name.trim(),
           domain: domain.trim() || undefined,
+          ...market,
         },
       }),
     onSuccess: async () => {
@@ -89,7 +95,9 @@ function GeneralSection({ project }: { project: ProjectSummary }) {
 
   const isDirty =
     name.trim() !== project.name ||
-    (domain.trim() || "") !== (project.domain ?? "");
+    (domain.trim() || "") !== (project.domain ?? "") ||
+    market.locationCode !== project.locationCode ||
+    market.languageCode !== project.languageCode;
 
   const handleSubmit = (event: React.FormEvent) => {
     event.preventDefault();
@@ -130,6 +138,14 @@ function GeneralSection({ project }: { project: ProjectSummary }) {
           />
         </label>
 
+        <div className="flex flex-col gap-1.5">
+          <ProjectMarketFields value={market} onChange={setMarket} />
+          <span className="text-xs text-base-content/50">
+            Keyword, SERP, and domain data uses this country and language unless
+            a call asks for a different one.
+          </span>
+        </div>
+
         <div className="flex justify-end">
           <button
             type="submit"
diff --git a/src/client/features/projects/types.ts b/src/client/features/projects/types.ts
index 22d3a49..44eabd6 100644
--- a/src/client/features/projects/types.ts
+++ b/src/client/features/projects/types.ts
@@ -1,7 +1,14 @@
+// The project's default market: the country/language pair its data calls
+// fall back to. Mirrors resolveMarket's project argument in shared/.
+export type ProjectMarket = { locationCode: number; languageCode: string };
+
 // Shape returned by the getProjects server function (a mapped project row).
 export type ProjectSummary = {
   id: string;
   name: string;
   domain: string | null;
+  // Default market for the project's data calls.
+  locationCode: number;
+  languageCode: string;
   createdAt: string;
 };
diff --git a/src/client/features/projects/useProjectMarket.ts b/src/client/features/projects/useProjectMarket.ts
new file mode 100644
index 0000000..bbf317c
--- /dev/null
+++ b/src/client/features/projects/useProjectMarket.ts
@@ -0,0 +1,13 @@
+import { useQuery } from "@tanstack/react-query";
+import { getProjects } from "@/serverFunctions/projects";
+import type { ProjectMarket } from "./types";
+
+/** The project's default market, or undefined until the projects query resolves. */
+export function useProjectMarket(projectId: string): ProjectMarket | undefined {
+  const projectsQuery = useQuery({
+    queryKey: ["projects"],
+    queryFn: () => getProjects(),
+  });
+
+  return projectsQuery.data?.find((project) => project.id === projectId);
+}
diff --git a/src/client/features/rank-tracking/KeywordSuggestionStep.tsx b/src/client/features/rank-tracking/KeywordSuggestionStep.tsx
index 8c2ba89..0aefc79 100644
--- a/src/client/features/rank-tracking/KeywordSuggestionStep.tsx
+++ b/src/client/features/rank-tracking/KeywordSuggestionStep.tsx
@@ -140,7 +140,6 @@ export function KeywordSuggestionStep({
   projectId,
   domain,
   locationCode,
-  languageCode,
   onDone,
   onClose,
 }: Props) {
@@ -163,16 +162,10 @@ export function KeywordSuggestionStep({
   // Ads keyword data (e.g. Iceland) have no ranking data to suggest from.
   const labsSupported = isLabsLocationCode(locationCode);
   const suggestionsQuery = useQuery({
-    queryKey: [
-      "domainKeywordSuggestions",
-      projectId,
-      domain,
-      locationCode,
-      languageCode,
-    ],
+    queryKey: ["domainKeywordSuggestions", projectId, domain, locationCode],
     queryFn: () =>
       getDomainKeywordSuggestions({
-        data: { projectId, domain, locationCode, languageCode },
+        data: { projectId, domain, locationCode },
       }),
     enabled: labsSupported,
   });
diff --git a/src/client/features/rank-tracking/RankTrackingConfigModal.tsx b/src/client/features/rank-tracking/RankTrackingConfigModal.tsx
index 69a1607..4599a0e 100644
--- a/src/client/features/rank-tracking/RankTrackingConfigModal.tsx
+++ b/src/client/features/rank-tracking/RankTrackingConfigModal.tsx
@@ -10,12 +10,13 @@ import {
   estimateRankCheckCredits,
 } from "@/shared/rank-tracking";
 import {
-  DEFAULT_LOCATION_CODE,
   getLanguageCode,
   getLanguageOptions,
 } from "@/client/features/keywords/locations";
 import { getIsoCountryCode } from "@/shared/keyword-locations";
 import { LocationSelect } from "@/client/components/LocationSelect";
+import type { ProjectMarket } from "@/client/features/projects/types";
+import { useProjectMarket } from "@/client/features/projects/useProjectMarket";
 import { SearchTargetingField } from "./SearchTargetingField";
 import { KeywordSuggestionStep } from "./KeywordSuggestionStep";
 import { useSaveConfigMutations } from "./useSaveConfigMutations";
@@ -35,6 +36,45 @@ export function RankTrackingConfigModal({
   onSaved,
   onConfigCreated,
 }: Props) {
+  const projectMarket = useProjectMarket(projectId);
+
+  if (!existingConfig && !projectMarket) {
+    return (
+      <Modal
+        maxWidth="max-w-lg"
+        onClose={onClose}
+        labelledBy="rank-config-modal-title"
+      >
+        <h2 id="rank-config-modal-title" className="sr-only">
+          Add Domain
+        </h2>
+        <div className="flex min-h-40 items-center justify-center">
+          <Loader2 className="size-5 animate-spin text-base-content/50" />
+        </div>
+      </Modal>
+    );
+  }
+
+  return (
+    <RankTrackingConfigModalContent
+      projectId={projectId}
+      existingConfig={existingConfig}
+      initialMarket={existingConfig ?? projectMarket!}
+      onClose={onClose}
+      onSaved={onSaved}
+      onConfigCreated={onConfigCreated}
+    />
+  );
+}
+
+function RankTrackingConfigModalContent({
+  projectId,
+  existingConfig,
+  initialMarket,
+  onClose,
+  onSaved,
+  onConfigCreated,
+}: Props & { initialMarket: ProjectMarket }) {
   const isEdit = !!existingConfig;
   const [step, setStep] = useState<"config" | "keywords">("config");
   const [domain, setDomain] = useState(existingConfig?.domain ?? "");
@@ -42,11 +82,10 @@ export function RankTrackingConfigModal({
     existingConfig?.devices ?? "mobile",
   );
   const [locationCode, setLocationCode] = useState(
-    existingConfig?.locationCode ?? DEFAULT_LOCATION_CODE,
+    existingConfig?.locationCode ?? initialMarket.locationCode,
   );
   const [languageCode, setLanguageCode] = useState(
-    existingConfig?.languageCode ??
-      getLanguageCode(existingConfig?.locationCode ?? DEFAULT_LOCATION_CODE),
+    existingConfig?.languageCode ?? initialMarket.languageCode,
   );
   const languageOptions = useMemo(
     () => getLanguageOptions(locationCode),
diff --git a/src/client/features/search-tabs/SearchTabStrip.tsx b/src/client/features/search-tabs/SearchTabStrip.tsx
index c4c9dd5..4bb9b4d 100644
--- a/src/client/features/search-tabs/SearchTabStrip.tsx
+++ b/src/client/features/search-tabs/SearchTabStrip.tsx
@@ -9,7 +9,6 @@ import {
   buildKeywordResearchRequest,
   keywordResearchQueryFn,
 } from "@/client/features/keywords/hooks/useKeywordResearchData";
-import { getLanguageCode } from "@/client/features/keywords/locations";
 import { getBacklinksOverview } from "@/serverFunctions/backlinks";
 import { getDomainOverview } from "@/serverFunctions/domain";
 export type { SearchTab } from "./types";
@@ -187,7 +186,6 @@ function getSearchTabQueryConfig(
   if (tab.input.type === "domain") {
     const input = tab.input;
     const trimmedDomain = input.domain.trim();
-    const languageCode = getLanguageCode(input.locationCode);
 
     return {
       queryKey: [
@@ -196,7 +194,6 @@ function getSearchTabQueryConfig(
         trimmedDomain,
         input.subdomains,
         input.locationCode,
-        languageCode,
       ],
       queryFn: () =>
         getDomainOverview({
@@ -205,7 +202,6 @@ function getSearchTabQueryConfig(
             domain: trimmedDomain,
             includeSubdomains: input.subdomains,
             locationCode: input.locationCode,
-            languageCode,
           },
         }),
       staleTime: 5 * 60_000,
diff --git a/src/client/features/search-tabs/types.ts b/src/client/features/search-tabs/types.ts
index ee21d64..bef8f60 100644
--- a/src/client/features/search-tabs/types.ts
+++ b/src/client/features/search-tabs/types.ts
@@ -14,13 +14,13 @@ export type DomainSearchTabInput = {
   type: "domain";
   domain: string;
   subdomains: boolean;
-  locationCode: number;
+  locationCode?: number;
 };
 
 export type KeywordSearchTabInput = {
   type: "keyword";
   keyword: string;
-  locationCode: number;
+  locationCode?: number;
   resultLimit: ResultLimit;
   mode: KeywordMode;
   clickstream: boolean;
diff --git a/src/client/features/search-tabs/useSearchTabNavigation.ts b/src/client/features/search-tabs/useSearchTabNavigation.ts
index c43c2cb..d46f0e1 100644
--- a/src/client/features/search-tabs/useSearchTabNavigation.ts
+++ b/src/client/features/search-tabs/useSearchTabNavigation.ts
@@ -9,7 +9,7 @@ type UseSearchTabNavigationArgs = {
   navigateToInput: (input: SearchTabInput | null) => void;
 };
 
-function tabInputKey(input: SearchTabInput | null) {
+export function tabInputKey(input: SearchTabInput | null) {
   return input ? JSON.stringify(input) : "";
 }
 
diff --git a/src/routes/_project/p/$projectId/domain.tsx b/src/routes/_project/p/$projectId/domain.tsx
index 416cf99..7bc53f9 100644
--- a/src/routes/_project/p/$projectId/domain.tsx
+++ b/src/routes/_project/p/$projectId/domain.tsx
@@ -8,8 +8,8 @@ import {
   DEFAULT_DOMAIN_KEYWORDS_PAGE_SIZE,
   domainSearchSchema,
 } from "@/types/schemas/domain";
-import { DEFAULT_LOCATION_CODE } from "@/client/features/keywords/locations";
 import { getDomainRouteState } from "@/client/features/domain/domainRouteState";
+import { useProjectMarket } from "@/client/features/projects/useProjectMarket";
 
 const DEFAULT_DOMAIN_SEARCH = {
   domain: "",
@@ -17,7 +17,6 @@ const DEFAULT_DOMAIN_SEARCH = {
   sort: "traffic",
   order: undefined,
   tab: "keywords",
-  loc: DEFAULT_LOCATION_CODE,
   page: 1,
   size: DEFAULT_DOMAIN_KEYWORDS_PAGE_SIZE,
   include: "",
@@ -52,7 +51,8 @@ function DomainOverviewRoute() {
   const { projectId } = Route.useParams();
   const navigate = useNavigate({ from: Route.fullPath });
   const search = Route.useSearch();
-  const routeState = getDomainRouteState(search);
+  const projectMarket = useProjectMarket(projectId);
+  const routeState = getDomainRouteState(search, projectMarket);
 
   return (
     <DomainOverviewPage
diff --git a/src/routes/_project/p/$projectId/keywords.tsx b/src/routes/_project/p/$projectId/keywords.tsx
index 848a962..ca79fac 100644
--- a/src/routes/_project/p/$projectId/keywords.tsx
+++ b/src/routes/_project/p/$projectId/keywords.tsx
@@ -1,5 +1,4 @@
 import { createFileRoute, redirect } from "@tanstack/react-router";
-import { DEFAULT_LOCATION_CODE } from "@/client/features/keywords/locations";
 import { KeywordResearchPage } from "@/client/features/keywords/page/KeywordResearchPage";
 import {
   isResultLimit,
@@ -31,20 +30,17 @@ function KeywordResearchPageRoute() {
   const search = Route.useSearch();
   const {
     q: keywordInput = "",
-    loc: rawLocationCode,
+    loc: locationCode,
     kLimit: resultLimit = 150,
     mode: keywordMode = "auto",
     sort: sortField = "searchVolume",
     order: sortDir = "desc",
   } = search;
-  const locationCode = rawLocationCode ?? DEFAULT_LOCATION_CODE;
-
   return (
     <KeywordResearchPage
       projectId={projectId}
       keywordInput={keywordInput}
       locationCode={locationCode}
-      hasExplicitLocationCode={search.loc != null}
       resultLimit={isResultLimit(resultLimit) ? resultLimit : 150}
       keywordMode={normalizeKeywordMode(keywordMode)}
       clickstream={search.cs ?? false}
diff --git a/src/server/features/keywords/services/research/research.ts b/src/server/features/keywords/services/research/research.ts
index 895b841..248627f 100644
--- a/src/server/features/keywords/services/research/research.ts
+++ b/src/server/features/keywords/services/research/research.ts
@@ -9,7 +9,7 @@ import {
 } from "@/server/lib/r2-cache";
 import { KeywordResearchRepository } from "@/server/features/keywords/repositories/KeywordResearchRepository";
 import type { KeywordResearchRow } from "@/types/keywords";
-import type { ResearchKeywordsInput } from "@/types/schemas/keywords";
+import type { ResolvedResearchKeywordsInput } from "@/types/schemas/keywords";
 import { z } from "zod";
 import { getKeywordDataProvider } from "@/shared/keyword-locations";
 import { type EnrichedKeyword, normalizeKeyword } from "./helpers";
@@ -93,7 +93,7 @@ const CACHE_VERSION = 3;
 
 async function fetchRowsFromSource(
   source: KeywordSource,
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   seedKeyword: string,
   billingCustomer: BillingCustomerContext,
   creditFeature?: CreditFeature,
@@ -113,7 +113,7 @@ async function fetchRowsFromSource(
 }
 
 async function fetchAutoRows(
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   seedKeyword: string,
   billingCustomer: BillingCustomerContext,
   creditFeature?: CreditFeature,
@@ -175,7 +175,7 @@ async function fetchAutoRows(
 }
 
 async function fetchGoogleAdsRows(
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   seedKeyword: string,
   billingCustomer: BillingCustomerContext,
   creditFeature?: CreditFeature,
@@ -211,7 +211,7 @@ async function fetchGoogleAdsRows(
 
 async function fetchManualRows(
   mode: Exclude<KeywordMode, "auto">,
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   seedKeyword: string,
   billingCustomer: BillingCustomerContext,
   creditFeature?: CreditFeature,
@@ -242,7 +242,7 @@ async function fetchManualRows(
 }
 
 async function buildResearchCacheKey(
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   normalizedKeywords: string[],
   mode: KeywordMode,
   billingCustomer: BillingCustomerContext,
@@ -261,7 +261,10 @@ async function buildResearchCacheKey(
   });
 }
 
-function persistRows(input: ResearchKeywordsInput, rows: EnrichedKeyword[]) {
+function persistRows(
+  input: ResolvedResearchKeywordsInput,
+  rows: EnrichedKeyword[],
+) {
   void Promise.all(
     rows.map((row) =>
       KeywordResearchRepository.upsertKeywordMetric({
@@ -283,7 +286,7 @@ function persistRows(input: ResearchKeywordsInput, rows: EnrichedKeyword[]) {
 }
 
 export async function research(
-  input: ResearchKeywordsInput,
+  input: ResolvedResearchKeywordsInput,
   billingCustomer: BillingCustomerContext,
   creditFeature?: CreditFeature,
 ): Promise<ResearchResult> {
@@ -300,7 +303,7 @@ export async function research(
   // Labs source modes and clickstream refinement don't exist for
   // Google-Ads-served countries; collapse both so equivalent requests share
   // one cache entry.
-  const effectiveInput: ResearchKeywordsInput =
+  const effectiveInput: ResolvedResearchKeywordsInput =
     provider === "google_ads"
       ? { ...input, mode: "auto", clickstream: false }
       : input;
diff --git a/src/server/features/keywords/services/research/saved-keywords.ts b/src/server/features/keywords/services/research/saved-keywords.ts
index e5ecc67..b1703b7 100644
--- a/src/server/features/keywords/services/research/saved-keywords.ts
+++ b/src/server/features/keywords/services/research/saved-keywords.ts
@@ -5,7 +5,7 @@ import type {
   ExportSavedKeywordsInput,
   GetSavedKeywordsInput,
   RemoveSavedKeywordsInput,
-  SaveKeywordsInput,
+  ResolvedSaveKeywordsInput,
   UpdateSavedKeywordTagInput,
   UpdateSavedKeywordTagsInput,
 } from "@/types/schemas/keywords";
@@ -31,7 +31,7 @@ function parseMonthlySearches(payload: string | null): MonthlySearch[] {
   return result.success ? result.data : [];
 }
 
-export async function saveKeywords(input: SaveKeywordsInput) {
+export async function saveKeywords(input: ResolvedSaveKeywordsInput) {
   const normalizedKeywords = [
     ...new Set(
       input.keywords.map(normalizeKeyword).filter((kw) => kw.length > 0),
diff --git a/src/server/features/projects/repositories/ProjectRepository.ts b/src/server/features/projects/repositories/ProjectRepository.ts
index 15b3290..f76b7b9 100644
--- a/src/server/features/projects/repositories/ProjectRepository.ts
+++ b/src/server/features/projects/repositories/ProjectRepository.ts
@@ -61,11 +61,13 @@ async function createProject(
   organizationId: string,
   name: string,
   domain?: string,
+  // Omitted keeps the column defaults.
+  market?: { locationCode: number; languageCode: string },
 ) {
   const id = crypto.randomUUID();
   const [row] = await db
     .insert(projects)
-    .values({ id, organizationId, name, domain })
+    .values({ id, organizationId, name, domain, ...market })
     .returning();
   return row;
 }
@@ -73,15 +75,48 @@ async function createProject(
 async function updateProject(
   projectId: string,
   organizationId: string,
-  input: { name: string; domain?: string },
+  input: {
+    name: string;
+    domain?: string;
+    // Omitted leaves the market columns untouched.
+    market?: { locationCode: number; languageCode: string };
+  },
 ) {
   const [row] = await db
     .update(projects)
-    .set({ name: input.name, domain: input.domain ?? null })
+    .set({ name: input.name, domain: input.domain ?? null, ...input.market })
     .where(
       and(
         eq(projects.id, projectId),
         eq(projects.organizationId, organizationId),
+        isNull(projects.archivedAt),
+      ),
+    )
+    .returning();
+
+  if (!row) {
+    throw new AppError("NOT_FOUND");
+  }
+
+  return row;
+}
+
+// Writes only the market columns. Onboarding sets the project's market before
+// the user has named the project or picked a domain, so it must not go through
+// updateProject, whose `domain: input.domain ?? null` would clear the domain.
+async function updateProjectMarket(
+  projectId: string,
+  organizationId: string,
+  market: { locationCode: number; languageCode: string },
+) {
+  const [row] = await db
+    .update(projects)
+    .set(market)
+    .where(
+      and(
+        eq(projects.id, projectId),
+        eq(projects.organizationId, organizationId),
+        isNull(projects.archivedAt),
       ),
     )
     .returning();
@@ -162,6 +197,7 @@ export const ProjectRepository = {
   getProjectById,
   createProject,
   updateProject,
+  updateProjectMarket,
   tryCreateDefaultProject,
   archiveProject,
   restoreProject,
diff --git a/src/server/features/projects/services/ProjectService.ts b/src/server/features/projects/services/ProjectService.ts
index 8b717fd..5489f4c 100644
--- a/src/server/features/projects/services/ProjectService.ts
+++ b/src/server/features/projects/services/ProjectService.ts
@@ -6,6 +6,7 @@ import {
   listProjects,
   listProjectsEnsuringOne,
   restoreProject,
+  setProjectMarket,
   updateProject,
 } from "@/server/features/projects/services/projects";
 
@@ -14,6 +15,7 @@ export const ProjectService = {
   listProjectsEnsuringOne,
   createProject,
   updateProject,
+  setProjectMarket,
   archiveProject,
   restoreProject,
   listArchivedProjects,
diff --git a/src/server/features/projects/services/projects.test.ts b/src/server/features/projects/services/projects.test.ts
index cfb5334..ac8b460 100644
--- a/src/server/features/projects/services/projects.test.ts
+++ b/src/server/features/projects/services/projects.test.ts
@@ -6,6 +6,7 @@ const mocks = vi.hoisted(() => ({
   archiveProject: vi.fn(),
   restoreProject: vi.fn(),
   countProjects: vi.fn(),
+  updateProjectMarket: vi.fn(),
   getProjectForOrganization: vi.fn(),
   listProjects: vi.fn(),
   listArchivedProjects: vi.fn(),
@@ -89,9 +90,40 @@ describe("project service", () => {
         "org_1",
         "Acme",
         "acme.com",
+        undefined,
       );
     });
 
+    it("derives the native language when only the location is given", async () => {
+      mocks.createProject.mockResolvedValue(namedProject);
+      const { createProject } = await import("./projects");
+
+      await createProject("org_1", {
+        name: "Acme",
+        domain: "acme.com",
+        locationCode: 2704,
+      });
+      expect(mocks.createProject).toHaveBeenCalledWith(
+        "org_1",
+        "Acme",
+        "acme.com",
+        { locationCode: 2704, languageCode: "vi" },
+      );
+    });
+
+    it("rejects a language DataForSEO does not serve for the location", async () => {
+      const { createProject } = await import("./projects");
+
+      await expect(
+        createProject("org_1", {
+          name: "Acme",
+          locationCode: 2840,
+          languageCode: "vi",
+        }),
+      ).rejects.toMatchObject({ code: "VALIDATION_ERROR" });
+      expect(mocks.createProject).not.toHaveBeenCalled();
+    });
+
     it("maps the reserved Default conflict to a friendly CONFLICT", async () => {
       mocks.createProject.mockRejectedValue(
         new Error(
@@ -107,6 +139,37 @@ describe("project service", () => {
   });
 
   describe("updateProject", () => {
+    it("leaves the market columns untouched when neither half is given", async () => {
+      mocks.updateProject.mockResolvedValue(namedProject);
+      const { updateProject } = await import("./projects");
+
+      await updateProject("org_1", { projectId: "project_acme", name: "Acme" });
+      expect(mocks.updateProject).toHaveBeenCalledWith(
+        "project_acme",
+        "org_1",
+        expect.objectContaining({ market: undefined }),
+      );
+    });
+
+    it("snaps the language on a location-only change without reading the stored row", async () => {
+      mocks.updateProject.mockResolvedValue(namedProject);
+      const { updateProject } = await import("./projects");
+
+      await updateProject("org_1", {
+        projectId: "project_acme",
+        name: "Acme",
+        locationCode: 2276,
+      });
+      expect(mocks.getProjectForOrganization).not.toHaveBeenCalled();
+      expect(mocks.updateProject).toHaveBeenCalledWith(
+        "project_acme",
+        "org_1",
+        expect.objectContaining({
+          market: { locationCode: 2276, languageCode: "de" },
+        }),
+      );
+    });
+
     it("returns the updated project", async () => {
       mocks.updateProject.mockResolvedValue(namedProject);
       const { updateProject } = await import("./projects");
@@ -145,6 +208,45 @@ describe("project service", () => {
     });
   });
 
+  describe("setProjectMarket", () => {
+    it("writes only the market columns, leaving name and domain untouched", async () => {
+      // Onboarding sets the market before the project is named or given a
+      // domain; going through updateProject would clear the domain.
+      mocks.updateProjectMarket.mockResolvedValue({
+        ...namedProject,
+        locationCode: 2704,
+        languageCode: "vi",
+      });
+      const { setProjectMarket } = await import("./projects");
+
+      await setProjectMarket("org_1", {
+        projectId: "project_acme",
+        locationCode: 2704,
+        languageCode: "vi",
+      });
+
+      expect(mocks.updateProjectMarket).toHaveBeenCalledWith(
+        "project_acme",
+        "org_1",
+        { locationCode: 2704, languageCode: "vi" },
+      );
+      expect(mocks.updateProject).not.toHaveBeenCalled();
+    });
+
+    it("rejects a language the location does not serve before any write", async () => {
+      const { setProjectMarket } = await import("./projects");
+
+      await expect(
+        setProjectMarket("org_1", {
+          projectId: "project_acme",
+          locationCode: 2840,
+          languageCode: "vi",
+        }),
+      ).rejects.toMatchObject({ code: "VALIDATION_ERROR" });
+      expect(mocks.updateProjectMarket).not.toHaveBeenCalled();
+    });
+  });
+
   describe("archiveProject", () => {
     it("refuses to archive the org's only project", async () => {
       mocks.countProjects.mockResolvedValue(1);
diff --git a/src/server/features/projects/services/projects.ts b/src/server/features/projects/services/projects.ts
index 276f9b6..dcfd8b8 100644
--- a/src/server/features/projects/services/projects.ts
+++ b/src/server/features/projects/services/projects.ts
@@ -2,25 +2,50 @@ import type {
   ArchiveProjectInput,
   CreateProjectInput,
   RestoreProjectInput,
+  SetProjectMarketInput,
   UpdateProjectInput,
 } from "@/types/schemas/projects";
 import { ProjectRepository } from "@/server/features/projects/repositories/ProjectRepository";
 import { AppError } from "@/server/lib/errors";
+import { assertLanguageForLocation } from "@/server/lib/market";
+import { getLanguageCode } from "@/shared/keyword-locations";
 
 function mapProject(project: {
   id: string;
   name: string;
   domain: string | null;
+  locationCode: number;
+  languageCode: string;
   createdAt: string;
 }) {
   return {
     id: project.id,
     name: project.name,
     domain: project.domain,
+    // Default market for the project's data calls (MCP tools and the web UI
+    // fall back to these when a call omits locationCode/languageCode).
+    locationCode: project.locationCode,
+    languageCode: project.languageCode,
     createdAt: project.createdAt,
   };
 }
 
+/**
+ * Resolves a market input into the columns to write. A location with no
+ * language snaps to that location's native language; the schemas forbid the
+ * reverse, so the pair is always resolvable without reading the stored row.
+ */
+function resolveMarketInput(input: {
+  locationCode?: number;
+  languageCode?: string;
+}): { locationCode: number; languageCode: string } | undefined {
+  if (input.locationCode == null) return undefined;
+  const locationCode = input.locationCode;
+  const languageCode = input.languageCode ?? getLanguageCode(locationCode);
+  assertLanguageForLocation(locationCode, languageCode);
+  return { locationCode, languageCode };
+}
+
 // The projects table's only unique index guards the auto-created ("Default",
 // null) singleton. A UNIQUE violation while writing exactly that name/domain
 // therefore means one already exists — gating on the input (not just the error
@@ -67,6 +92,7 @@ export async function createProject(
       organizationId,
       input.name,
       input.domain,
+      resolveMarketInput(input),
     );
     return mapProject(row);
   } catch (error) {
@@ -85,7 +111,11 @@ export async function updateProject(
     const row = await ProjectRepository.updateProject(
       input.projectId,
       organizationId,
-      { name: input.name, domain: input.domain },
+      {
+        name: input.name,
+        domain: input.domain,
+        market: resolveMarketInput(input),
+      },
     );
     return mapProject(row);
   } catch (error) {
@@ -96,6 +126,24 @@ export async function updateProject(
   }
 }
 
+/**
+ * Sets a project's default market on its own, for surfaces that only ask for
+ * the market (onboarding). Writing just these two columns keeps the write from
+ * echoing a name/domain the caller never edited.
+ */
+export async function setProjectMarket(
+  organizationId: string,
+  input: SetProjectMarketInput,
+) {
+  assertLanguageForLocation(input.locationCode, input.languageCode);
+  const row = await ProjectRepository.updateProjectMarket(
+    input.projectId,
+    organizationId,
+    { locationCode: input.locationCode, languageCode: input.languageCode },
+  );
+  return mapProject(row);
+}
+
 export async function archiveProject(
   organizationId: string,
   input: ArchiveProjectInput,
diff --git a/src/server/features/rank-tracking/services/RankTrackingService.test.ts b/src/server/features/rank-tracking/services/RankTrackingService.test.ts
index 61ed2bb..149d51c 100644
--- a/src/server/features/rank-tracking/services/RankTrackingService.test.ts
+++ b/src/server/features/rank-tracking/services/RankTrackingService.test.ts
@@ -29,6 +29,7 @@ const archivedConfig = {
 
 const baseInput = {
   projectId: "project_1",
+  projectMarket: { locationCode: 2704, languageCode: "vi" },
   domain: "acme.com",
   locationCode: 2840,
   languageCode: "es",
@@ -154,4 +155,41 @@ describe("RankTrackingService.createConfig", () => {
       }),
     );
   });
+
+  it("uses the project's market when location and language are omitted", async () => {
+    mocks.getConfigByProjectDomainLocation.mockResolvedValue(null);
+    mocks.getConfigsForProject.mockResolvedValue([]);
+    mocks.createConfig.mockResolvedValue(undefined);
+    const { RankTrackingService } = await import("./RankTrackingService");
+
+    await RankTrackingService.createConfig({
+      projectId: "project_1",
+      projectMarket: { locationCode: 2704, languageCode: "vi" },
+      domain: "acme.com",
+      serpDepth: 40,
+    });
+
+    expect(mocks.createConfig).toHaveBeenCalledWith(
+      expect.objectContaining({ locationCode: 2704, languageCode: "vi" }),
+    );
+  });
+
+  it("snaps the language when only location overrides the project market", async () => {
+    mocks.getConfigByProjectDomainLocation.mockResolvedValue(null);
+    mocks.getConfigsForProject.mockResolvedValue([]);
+    mocks.createConfig.mockResolvedValue(undefined);
+    const { RankTrackingService } = await import("./RankTrackingService");
+
+    await RankTrackingService.createConfig({
+      projectId: "project_1",
+      projectMarket: { locationCode: 2704, languageCode: "vi" },
+      domain: "acme.com",
+      locationCode: 2276,
+      serpDepth: 40,
+    });
+
+    expect(mocks.createConfig).toHaveBeenCalledWith(
+      expect.objectContaining({ locationCode: 2276, languageCode: "de" }),
+    );
+  });
 });
diff --git a/src/server/features/rank-tracking/services/RankTrackingService.ts b/src/server/features/rank-tracking/services/RankTrackingService.ts
index 9b4380f..ed699b3 100644
--- a/src/server/features/rank-tracking/services/RankTrackingService.ts
+++ b/src/server/features/rank-tracking/services/RankTrackingService.ts
@@ -22,6 +22,7 @@ import {
   MAX_KEYWORDS_PER_CONFIG,
   MAX_CONFIGS_PER_PROJECT,
 } from "@/shared/rank-tracking";
+import { resolveMarket } from "@/shared/keyword-locations";
 
 // ---------------------------------------------------------------------------
 // Config
@@ -29,6 +30,7 @@ import {
 
 async function createConfig(input: {
   projectId: string;
+  projectMarket: { locationCode: number; languageCode: string };
   domain: string;
   locationCode?: number;
   languageCode?: string;
@@ -39,7 +41,10 @@ async function createConfig(input: {
 }) {
   const normalizedDomain = normalizeDomain(input.domain);
 
-  const locationCode = input.locationCode ?? 2840;
+  const { locationCode, languageCode } = resolveMarket(
+    input,
+    input.projectMarket,
+  );
   const scheduleInterval = input.scheduleInterval ?? "weekly";
   const nextCheckAt = isScheduledRankTrackingInterval(scheduleInterval)
     ? computeNextCheckAt(scheduleInterval)
@@ -82,7 +87,7 @@ async function createConfig(input: {
   if (existing) {
     await RankTrackingRepository.updateConfig(existing.id, input.projectId, {
       isActive: true,
-      languageCode: input.languageCode ?? "en",
+      languageCode,
       devices: input.devices ?? "both",
       serpDepth: input.serpDepth,
       scheduleInterval,
@@ -102,7 +107,7 @@ async function createConfig(input: {
     projectId: input.projectId,
     domain: normalizedDomain,
     locationCode,
-    languageCode: input.languageCode ?? "en",
+    languageCode,
     locationName,
     devices: input.devices ?? "both",
     serpDepth: input.serpDepth,
diff --git a/src/server/lib/market.ts b/src/server/lib/market.ts
new file mode 100644
index 0000000..6ef30fb
--- /dev/null
+++ b/src/server/lib/market.ts
@@ -0,0 +1,43 @@
+import { AppError } from "@/server/lib/errors";
+import {
+  DEFAULT_LOCATION_CODE,
+  getKeywordDataProvider,
+  getLanguageOptions,
+  isLanguageServedForLocation,
+} from "@/shared/keyword-locations";
+
+/**
+ * Guards Labs-backed tools (domain analytics) against locations we serve
+ * from Google Ads keyword data only.
+ */
+export function assertLabsLocationCode(locationCode: number | undefined) {
+  if (locationCode != null && getKeywordDataProvider(locationCode) !== "labs") {
+    throw new AppError(
+      "VALIDATION_ERROR",
+      "Domain analytics is not available for this country. Keyword research and rank tracking work; domain-level data is limited to DataForSEO Labs locations.",
+    );
+  }
+}
+
+/**
+ * Guards Labs-backed callers against a language DataForSEO doesn't serve for
+ * the chosen location. A mismatched pair (e.g. language_code="ru" for the
+ * United States) is otherwise rejected as an opaque *charged* "Invalid Field:
+ * 'language_code'." task failure, so validate the pair first (cost 0).
+ */
+export function assertLanguageForLocation(
+  locationCode: number | undefined,
+  languageCode: string | undefined,
+) {
+  if (languageCode == null) return;
+  const resolvedLocation = locationCode ?? DEFAULT_LOCATION_CODE;
+  if (isLanguageServedForLocation(resolvedLocation, languageCode)) return;
+  throw new AppError(
+    "VALIDATION_ERROR",
+    `Language '${languageCode}' is not available for this location. Available: ${getLanguageOptions(
+      resolvedLocation,
+    )
+      .map((option) => option.code)
+      .join(", ")}.`,
+  );
+}
diff --git a/src/server/mcp/project-auth.test.ts b/src/server/mcp/project-auth.test.ts
index 6ae3956..9861583 100644
--- a/src/server/mcp/project-auth.test.ts
+++ b/src/server/mcp/project-auth.test.ts
@@ -46,6 +46,8 @@ describe("withMcpProjectAuth", () => {
     mocks.getProjectForOrganization.mockResolvedValue({
       id: "project_123",
       name: "Test",
+      locationCode: 2840,
+      languageCode: "en",
     });
   });
 
@@ -64,7 +66,7 @@ describe("withMcpProjectAuth", () => {
     );
   });
 
-  it("passes auth, baseUrl, and billing context to the wrapped handler", async () => {
+  it("passes auth, baseUrl, billing, and project context to the wrapped handler", async () => {
     const { withMcpProjectAuth } = await import("@/server/mcp/project-auth");
     const handler = vi.fn().mockReturnValue("ok");
 
@@ -90,6 +92,12 @@ describe("withMcpProjectAuth", () => {
           organizationId: "org_123",
           projectId: "project_123",
         },
+        project: {
+          id: "project_123",
+          name: "Test",
+          locationCode: 2840,
+          languageCode: "en",
+        },
       },
     );
   });
diff --git a/src/server/mcp/project-auth.ts b/src/server/mcp/project-auth.ts
index 2326a42..0eb0f26 100644
--- a/src/server/mcp/project-auth.ts
+++ b/src/server/mcp/project-auth.ts
@@ -28,6 +28,9 @@ async function requireProjectAccess(extra: ToolExtra, projectId: string) {
     auth,
     baseUrl,
     billing: buildBillingCustomer(auth, projectId),
+    // The row is already fetched for the auth gate; exposing it lets tools
+    // fall back to the project's default market without another query.
+    project,
   };
 }
 
diff --git a/src/server/mcp/schemas.ts b/src/server/mcp/schemas.ts
index 7c95dea..18a3ba4 100644
--- a/src/server/mcp/schemas.ts
+++ b/src/server/mcp/schemas.ts
@@ -1,13 +1,7 @@
 import { z } from "zod";
-import { AppError } from "@/server/lib/errors";
-import {
-  getKeywordDataProvider,
-  getLanguageOptions,
-  isSupportedLanguageCode,
-} from "@/shared/keyword-locations";
+import { isSupportedLanguageCode } from "@/shared/keyword-locations";
 
 export const DEFAULT_LOCATION_CODE = 2840;
-export const DEFAULT_LANGUAGE_CODE = "en";
 
 export const projectIdSchema = z
   .string()
@@ -21,52 +15,15 @@ export const locationCodeSchema = z
   .int()
   .positive()
   .describe(
-    "DataForSEO location code. Defaults to 2840 (United States). See dataforseo.com/help-center/locations. Some countries (e.g. Iceland, 2352) are served from Google Ads data: keyword volume/CPC/trends work, but keyword difficulty, search intent, and domain analytics are unavailable.",
+    "DataForSEO location code. Defaults to the project's default market (see list_projects; editable in project settings). See dataforseo.com/help-center/locations. Some countries (e.g. Iceland, 2352) are served from Google Ads data: keyword volume/CPC/trends work, but keyword difficulty, search intent, and domain analytics are unavailable.",
   );
 
-/**
- * Guards Labs-backed tools (domain analytics) against locations we serve
- * from Google Ads keyword data only.
- */
-export function assertLabsLocationCode(locationCode: number | undefined) {
-  if (locationCode != null && getKeywordDataProvider(locationCode) !== "labs") {
-    throw new AppError(
-      "VALIDATION_ERROR",
-      "Domain analytics is not available for this country. Keyword research and rank tracking work; domain-level data is limited to DataForSEO Labs locations.",
-    );
-  }
-}
-
-/**
- * Guards Labs-backed tools against a language DataForSEO doesn't serve for the
- * chosen location. A mismatched pair (e.g. language_code="ru" for the United
- * States) is otherwise rejected as an opaque *charged* "Invalid Field:
- * 'language_code'." task failure, so validate the pair first (cost 0). Only
- * Labs locations have authoritative per-location language lists; Google Ads
- * locations are left to the metering safety net.
- */
-export function assertLanguageForLocation(
-  locationCode: number | undefined,
-  languageCode: string | undefined,
-) {
-  if (languageCode == null) return;
-  const resolvedLocation = locationCode ?? DEFAULT_LOCATION_CODE;
-  if (getKeywordDataProvider(resolvedLocation) !== "labs") return;
-  const options = getLanguageOptions(resolvedLocation);
-  if (!options.some((option) => option.code === languageCode)) {
-    throw new AppError(
-      "VALIDATION_ERROR",
-      `Language '${languageCode}' is not available for this location. Available: ${options
-        .map((option) => option.code)
-        .join(", ")}.`,
-    );
-  }
-}
-
 export const languageCodeSchema = z
   .string()
   .refine(isSupportedLanguageCode, {
     message:
       "Unsupported language code. Use a supported code such as 'en', 'es', 'de', or 'fr'.",
   })
-  .describe("Language code (e.g. 'en', 'es', 'fr'). Defaults to 'en'.");
+  .describe(
+    "Language code (e.g. 'en', 'es', 'vi'). Defaults to the project's default market language (see list_projects).",
+  );
diff --git a/src/server/mcp/tools/dataforseo-research-tools.google-ads.test.ts b/src/server/mcp/tools/dataforseo-research-tools.google-ads.test.ts
index db1c471..18faf67 100644
--- a/src/server/mcp/tools/dataforseo-research-tools.google-ads.test.ts
+++ b/src/server/mcp/tools/dataforseo-research-tools.google-ads.test.ts
@@ -62,7 +62,11 @@ describe("get_keyword_metrics for Google-Ads-only locations", () => {
     vi.resetModules();
     mocks.createDataforseoClient.mockReset();
     mocks.getProjectForOrganization.mockReset();
-    mocks.getProjectForOrganization.mockResolvedValue({ id: "project_1" });
+    mocks.getProjectForOrganization.mockResolvedValue({
+      id: "project_1",
+      locationCode: 2840,
+      languageCode: "en",
+    });
   });
 
   it("serves Iceland from adsSearchVolume without KD/intent", async () => {
diff --git a/src/server/mcp/tools/dataforseo-research-tools.market.test.ts b/src/server/mcp/tools/dataforseo-research-tools.market.test.ts
new file mode 100644
index 0000000..63170cd
--- /dev/null
+++ b/src/server/mcp/tools/dataforseo-research-tools.market.test.ts
@@ -0,0 +1,114 @@
+import type { AuthInfo } from "@modelcontextprotocol/sdk/server/auth/types.js";
+import type { ToolExtra } from "@/server/mcp/context";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { MCP_AUTH_CONTEXT_PROP } from "@/server/mcp/context";
+
+// Market resolution for get_ranked_keywords: the explicit country selector and
+// the project's default-market fallback (projects.locationCode/languageCode).
+// find_serp_competitors resolves through the same resolveMarketSelector.
+
+const mocks = vi.hoisted(() => ({
+  createDataforseoClient: vi.fn(),
+  getProjectForOrganization: vi.fn(),
+}));
+
+vi.mock("cloudflare:workers", () => ({ env: {} }));
+
+vi.mock("@/server/lib/dataforseo", () => ({
+  createDataforseoClient: mocks.createDataforseoClient,
+  fetchKeywordMetricsForList: vi.fn(),
+}));
+
+vi.mock("@/server/features/projects/services/ProjectService", () => ({
+  ProjectService: {
+    getProjectForOrganization: mocks.getProjectForOrganization,
+  },
+}));
+
+const authContext = {
+  userId: "user_123",
+  userEmail: "alice@example.com",
+  organizationId: "org_123",
+  clientId: "client_123",
+  scopes: ["mcp"],
+  audience: "https://open-seo.test/mcp",
+  subject: "user_123",
+  baseUrl: "https://open-seo.test",
+};
+
+const toolExtra: ToolExtra = {
+  signal: new AbortController().signal,
+  requestId: 1,
+  sendNotification: vi.fn(),
+  sendRequest: vi.fn(),
+  authInfo: {
+    token: "token",
+    clientId: "client_123",
+    scopes: ["mcp"],
+    resource: new URL("https://open-seo.test/mcp"),
+    extra: { [MCP_AUTH_CONTEXT_PROP]: authContext },
+  } satisfies AuthInfo,
+};
+
+function setProject(market: { locationCode: number; languageCode: string }) {
+  mocks.getProjectForOrganization.mockResolvedValue({
+    id: "project_1",
+    name: "Test",
+    domain: null,
+    createdAt: "2026-01-01T00:00:00.000Z",
+    ...market,
+  });
+}
+
+async function runRankedKeywords(args: { market?: { country: "US" } }) {
+  const rankedKeywords = vi.fn().mockResolvedValue({
+    items: [],
+    totalCount: 0,
+  });
+  mocks.createDataforseoClient.mockReturnValue({
+    domain: { rankedKeywords },
+  });
+  const { getRankedKeywordsTool } = await import("./dataforseo-research-tools");
+  await getRankedKeywordsTool.handler(
+    { projectId: "project_1", target: "acmeexample.com", ...args },
+    toolExtra,
+  );
+  return rankedKeywords;
+}
+
+describe("market resolution for Labs tools", () => {
+  beforeEach(() => {
+    vi.resetModules();
+    mocks.createDataforseoClient.mockReset();
+    mocks.getProjectForOrganization.mockReset();
+    setProject({ locationCode: 2840, languageCode: "en" });
+  });
+
+  it("keeps the US when market is explicit even for a non-US project", async () => {
+    setProject({ locationCode: 2704, languageCode: "vi" });
+    const rankedKeywords = await runRankedKeywords({
+      market: { country: "US" },
+    });
+    expect(rankedKeywords).toHaveBeenCalledWith(
+      expect.objectContaining({ locationCode: 2840, languageCode: "en" }),
+    );
+  });
+
+  it("follows the project's default market when the market object is omitted", async () => {
+    setProject({ locationCode: 2704, languageCode: "vi" });
+    const rankedKeywords = await runRankedKeywords({});
+    expect(rankedKeywords).toHaveBeenCalledWith(
+      expect.objectContaining({ locationCode: 2704, languageCode: "vi" }),
+    );
+  });
+
+  it("falls back to the US when the project market is not Labs-served", async () => {
+    // Iceland (2352) is served from Google Ads data; the Labs-only market
+    // tools must not inherit it.
+    setProject({ locationCode: 2352, languageCode: "en" });
+    const rankedKeywords = await runRankedKeywords({});
+    expect(rankedKeywords).toHaveBeenCalledWith(
+      expect.objectContaining({ locationCode: 2840, languageCode: "en" }),
+    );
+  });
+});
diff --git a/src/server/mcp/tools/dataforseo-research-tools.test.ts b/src/server/mcp/tools/dataforseo-research-tools.test.ts
index 16228ea..059a96b 100644
--- a/src/server/mcp/tools/dataforseo-research-tools.test.ts
+++ b/src/server/mcp/tools/dataforseo-research-tools.test.ts
@@ -64,12 +64,18 @@ function textOf(result: {
   return first?.type === "text" ? (first.text ?? "") : "";
 }
 
+const usProjectRow = {
+  id: "project_1",
+  locationCode: 2840,
+  languageCode: "en",
+};
+
 describe("DataForSEO research MCP tools", () => {
   beforeEach(() => {
     vi.resetModules();
     mocks.createDataforseoClient.mockReset();
     mocks.getProjectForOrganization.mockReset();
-    mocks.getProjectForOrganization.mockResolvedValue({ id: "project_1" });
+    mocks.getProjectForOrganization.mockResolvedValue(usProjectRow);
   });
 
   it("searches local businesses without running rankings or Q&A", async () => {
diff --git a/src/server/mcp/tools/dataforseo-research-tools.ts b/src/server/mcp/tools/dataforseo-research-tools.ts
index 7d79626..cbd6a49 100644
--- a/src/server/mcp/tools/dataforseo-research-tools.ts
+++ b/src/server/mcp/tools/dataforseo-research-tools.ts
@@ -17,10 +17,10 @@ import {
   readPath,
   type McpTableColumn,
 } from "@/server/mcp/table";
+import { resolveLabsMarket, resolveMarket } from "@/shared/keyword-locations";
+import { assertLanguageForLocation } from "@/server/lib/market";
 import {
-  DEFAULT_LANGUAGE_CODE,
   DEFAULT_LOCATION_CODE,
-  assertLanguageForLocation,
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -46,10 +46,14 @@ const marketSchema = z
     country: z
       .enum(["US", "USA", "United States", "United States of America"])
       .optional()
-      .describe("Country selector. Only the United States is supported."),
+      .describe(
+        "Country selector. Only the United States can be selected explicitly.",
+      ),
   })
   .optional()
-  .describe("Optional United States market object. Defaults to United States.");
+  .describe(
+    "Optional market object. Omitted = the project's default market (United States unless the project overrides it).",
+  );
 
 const nearSchema = z
   .object({
@@ -344,10 +348,20 @@ type GetGoogleBusinessQuestionsArgs = z.infer<
 const QUESTIONS_ANSWERS_MIN_RADIUS = 200;
 const QUESTIONS_ANSWERS_MAX_RADIUS = 199999;
 
-function resolveMarketLocationCode(_market: Market | undefined): number {
-  // The Zod enum on market.country already restricts values to United States
-  // variants, so no other country can reach this code path.
-  return DEFAULT_LOCATION_CODE;
+/**
+ * Resolves the market selector to a Labs location + language. An explicit
+ * country wins; omitted inherits the project's default via resolveLabsMarket,
+ * which keeps these Labs-only tools off an Ads-served project market.
+ */
+function resolveMarketSelector(
+  market: Market | undefined,
+  project: { locationCode: number; languageCode: string },
+): { locationCode: number; languageCode: string } {
+  if (market?.country != null) {
+    // The Zod enum already restricts explicit values to United States variants.
+    return { locationCode: DEFAULT_LOCATION_CODE, languageCode: "en" };
+  }
+  return resolveLabsMarket({}, project);
 }
 
 function formatCoordinate(value: number): string {
@@ -594,10 +608,11 @@ export const getRankedKeywordsTool = {
   handler: withMcpProjectAuth(async (args: GetRankedKeywordsArgs, context) => {
     const client = createDataforseoClient(context.billing);
     const targetIsPage = /^https?:\/\//.test(args.target);
+    const market = resolveMarketSelector(args.market, context.project);
     const keywords = await client.domain.rankedKeywords({
       target: args.target,
-      locationCode: resolveMarketLocationCode(args.market),
-      languageCode: DEFAULT_LANGUAGE_CODE,
+      locationCode: market.locationCode,
+      languageCode: market.languageCode,
       limit: args.limit ?? 50,
       offset: args.offset,
       orderBy: sortOrderByRankedMode(args.sortBy),
@@ -693,7 +708,7 @@ export const getLocalSerpResultsTool = {
       const results = await client.serp.local({
         keyword: args.keyword,
         locationCoordinate: formatLocalSerpCoordinate(args.near),
-        languageCode: args.languageCode ?? DEFAULT_LANGUAGE_CODE,
+        languageCode: args.languageCode ?? context.project.languageCode,
         searchType: args.searchType ?? "maps",
         device: args.device ?? "desktop",
         depth: args.depth ?? 20,
@@ -736,7 +751,7 @@ export const getGoogleBusinessQuestionsTool = {
       const questions = await client.business.questionsAnswers({
         keyword: args.keyword,
         locationCoordinate: formatQuestionsAnswersCoordinate(args.near),
-        languageCode: args.languageCode ?? DEFAULT_LANGUAGE_CODE,
+        languageCode: args.languageCode ?? context.project.languageCode,
         depth: args.depth ?? 20,
       });
 
@@ -773,10 +788,11 @@ export const findSerpCompetitorsTool = {
   handler: withMcpProjectAuth(
     async (args: FindSerpCompetitorsArgs, context) => {
       const client = createDataforseoClient(context.billing);
+      const market = resolveMarketSelector(args.market, context.project);
       const competitors = await client.labs.serpCompetitors({
         keywords: args.keywords,
-        locationCode: resolveMarketLocationCode(args.market),
-        languageCode: DEFAULT_LANGUAGE_CODE,
+        locationCode: market.locationCode,
+        languageCode: market.languageCode,
         itemTypes: args.resultTypes ?? ["organic", "local_pack"],
         includeSubdomains: args.includeSubdomains,
         limit: args.limit ?? 50,
@@ -829,10 +845,11 @@ export const getKeywordMetricsTool = {
     },
   },
   handler: withMcpProjectAuth(async (args: GetKeywordMetricsArgs, context) => {
-    assertLanguageForLocation(args.locationCode, args.languageCode);
+    const { locationCode, languageCode } = resolveMarket(args, context.project);
+    // Assert against the RESOLVED pair: an explicit language with an omitted
+    // location must validate against the project's default location.
+    assertLanguageForLocation(locationCode, languageCode);
     const client = createDataforseoClient(context.billing);
-    const locationCode = args.locationCode ?? DEFAULT_LOCATION_CODE;
-    const languageCode = args.languageCode ?? DEFAULT_LANGUAGE_CODE;
     const metrics = await fetchKeywordMetricsForList(client, {
       keywords: args.keywords,
       locationCode,
diff --git a/src/server/mcp/tools/get-domain-keyword-suggestions.ts b/src/server/mcp/tools/get-domain-keyword-suggestions.ts
index 14f1187..36b42dc 100644
--- a/src/server/mcp/tools/get-domain-keyword-suggestions.ts
+++ b/src/server/mcp/tools/get-domain-keyword-suggestions.ts
@@ -7,16 +7,17 @@ import {
   optionalMetaOutputSchema,
 } from "@/server/mcp/output-schemas";
 import { withMcpProjectAuth } from "@/server/mcp/project-auth";
+import { resolveLabsMarket } from "@/shared/keyword-locations";
 import {
   formatMcpTable,
   readPath,
   type McpTableColumn,
 } from "@/server/mcp/table";
 import {
-  DEFAULT_LANGUAGE_CODE,
-  DEFAULT_LOCATION_CODE,
   assertLabsLocationCode,
   assertLanguageForLocation,
+} from "@/server/lib/market";
+import {
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -59,13 +60,17 @@ export const getDomainKeywordSuggestionsTool = {
     },
   },
   handler: withMcpProjectAuth(async (args: Args, context) => {
-    assertLabsLocationCode(args.locationCode);
-    assertLanguageForLocation(args.locationCode, args.languageCode);
+    const { locationCode, languageCode } = resolveLabsMarket(
+      args,
+      context.project,
+    );
+    assertLabsLocationCode(locationCode);
+    assertLanguageForLocation(locationCode, languageCode);
     const keywords = await DomainService.getSuggestedKeywords(
       {
         domain: args.domain,
-        locationCode: args.locationCode ?? DEFAULT_LOCATION_CODE,
-        languageCode: args.languageCode ?? DEFAULT_LANGUAGE_CODE,
+        locationCode,
+        languageCode,
         organizationId: context.auth.organizationId,
         projectId: args.projectId,
       },
diff --git a/src/server/mcp/tools/get-domain-overview.ts b/src/server/mcp/tools/get-domain-overview.ts
index 4970562..d8ed693 100644
--- a/src/server/mcp/tools/get-domain-overview.ts
+++ b/src/server/mcp/tools/get-domain-overview.ts
@@ -4,11 +4,12 @@ import { mcpResponse } from "@/server/mcp/formatters";
 import { buildProjectMeta } from "@/server/mcp/context";
 import { optionalMetaOutputSchema } from "@/server/mcp/output-schemas";
 import { withMcpProjectAuth } from "@/server/mcp/project-auth";
+import { resolveLabsMarket } from "@/shared/keyword-locations";
 import {
-  DEFAULT_LANGUAGE_CODE,
-  DEFAULT_LOCATION_CODE,
   assertLabsLocationCode,
   assertLanguageForLocation,
+} from "@/server/lib/market";
+import {
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -52,15 +53,19 @@ export const getDomainOverviewTool = {
     },
   },
   handler: withMcpProjectAuth(async (args: Args, context) => {
-    assertLabsLocationCode(args.locationCode);
-    assertLanguageForLocation(args.locationCode, args.languageCode);
+    const { locationCode, languageCode } = resolveLabsMarket(
+      args,
+      context.project,
+    );
+    assertLabsLocationCode(locationCode);
+    assertLanguageForLocation(locationCode, languageCode);
     const result = await DomainService.getOverview(
       {
         projectId: args.projectId,
         domain: args.domain,
         includeSubdomains: args.includeSubdomains,
-        locationCode: args.locationCode ?? DEFAULT_LOCATION_CODE,
-        languageCode: args.languageCode ?? DEFAULT_LANGUAGE_CODE,
+        locationCode,
+        languageCode,
       },
       context.billing,
     );
diff --git a/src/server/mcp/tools/get-serp-results.ts b/src/server/mcp/tools/get-serp-results.ts
index 93e3a92..0843c6d 100644
--- a/src/server/mcp/tools/get-serp-results.ts
+++ b/src/server/mcp/tools/get-serp-results.ts
@@ -4,10 +4,9 @@ import { mcpResponse } from "@/server/mcp/formatters";
 import { buildProjectMeta } from "@/server/mcp/context";
 import { optionalMetaOutputSchema } from "@/server/mcp/output-schemas";
 import { withMcpProjectAuth } from "@/server/mcp/project-auth";
+import { resolveMarket } from "@/shared/keyword-locations";
 import { formatMcpTable, type McpTableColumn } from "@/server/mcp/table";
 import {
-  DEFAULT_LANGUAGE_CODE,
-  DEFAULT_LOCATION_CODE,
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -95,14 +94,12 @@ export const getSerpResultsTool = {
   },
   handler: withMcpProjectAuth(async (args: Args, context) => {
     const client = createDataforseoClient(context.billing);
-
     const results = await Promise.all(
       args.queries.map(async (q) => {
         try {
           const items = await client.serp.live({
             keyword: q.keyword,
-            locationCode: q.locationCode ?? DEFAULT_LOCATION_CODE,
-            languageCode: q.languageCode ?? DEFAULT_LANGUAGE_CODE,
+            ...resolveMarket(q, context.project),
           });
           // Trim noise — return only essentials per item.
           const trimmed = items.slice(0, 20).map((item) => ({
diff --git a/src/server/mcp/tools/list-projects.ts b/src/server/mcp/tools/list-projects.ts
index 1eccf35..0dc1bc2 100644
--- a/src/server/mcp/tools/list-projects.ts
+++ b/src/server/mcp/tools/list-projects.ts
@@ -13,7 +13,7 @@ export const listProjectsTool = {
   config: {
     title: "List projects",
     description:
-      "Lists all projects in the user's organization. Uses no credits — does not call DataForSEO. Use this whenever you need a `projectId` for another OpenSEO tool. Returns an array of {id, name, domain}; pass the `id` value as `projectId`.",
+      "Lists all projects in the user's organization. Uses no credits — does not call DataForSEO. Use this whenever you need a `projectId` for another OpenSEO tool. Returns an array of {id, name, domain, locationCode, languageCode}; pass the `id` value as `projectId`. locationCode/languageCode are the project's default market — tools fall back to them when a call omits location/language args.",
     inputSchema: {} as Record<string, never>,
     outputSchema: {
       projects: z.array(
@@ -22,6 +22,8 @@ export const listProjectsTool = {
             id: z.string(),
             name: z.string(),
             domain: z.string().nullable().optional(),
+            locationCode: z.number(),
+            languageCode: z.string(),
             url: z.string(),
           })
           .passthrough(),
@@ -41,7 +43,8 @@ export const listProjectsTool = {
       projects.length === 0
         ? ["No projects yet. Create one in the dashboard."]
         : projects.map(
-            (p) => `- ${p.id}  ${p.name}${p.domain ? ` (${p.domain})` : ""}`,
+            (p) =>
+              `- ${p.id}  ${p.name}${p.domain ? ` (${p.domain})` : ""}  market:${p.locationCode}/${p.languageCode}`,
           );
     return mcpResponse({
       text: `Projects (${projects.length}):\n${lines.join("\n")}`,
@@ -54,6 +57,8 @@ export const listProjectsTool = {
           id: p.id,
           name: p.name,
           domain: p.domain,
+          locationCode: p.locationCode,
+          languageCode: p.languageCode,
           url: buildDashboardUrl(baseUrl, `/p/${p.id}`),
         })),
       },
diff --git a/src/server/mcp/tools/output-schema-validation.test.ts b/src/server/mcp/tools/output-schema-validation.test.ts
index 3a185cc..3713942 100644
--- a/src/server/mcp/tools/output-schema-validation.test.ts
+++ b/src/server/mcp/tools/output-schema-validation.test.ts
@@ -99,7 +99,11 @@ const backlinkPage = {
 beforeEach(() => {
   mocks.getProjectForOrganization.mockReset();
   mocks.profileBacklinksPage.mockReset();
-  mocks.getProjectForOrganization.mockResolvedValue({ id: "project_123" });
+  mocks.getProjectForOrganization.mockResolvedValue({
+    id: "project_123",
+    locationCode: 2840,
+    languageCode: "en",
+  });
 });
 
 describe("DataForSEO research tool output schemas", () => {
diff --git a/src/server/mcp/tools/research-keywords.ts b/src/server/mcp/tools/research-keywords.ts
index 503e2ed..4686285 100644
--- a/src/server/mcp/tools/research-keywords.ts
+++ b/src/server/mcp/tools/research-keywords.ts
@@ -7,11 +7,10 @@ import {
   optionalMetaOutputSchema,
 } from "@/server/mcp/output-schemas";
 import { withMcpProjectAuth } from "@/server/mcp/project-auth";
+import { resolveMarket } from "@/shared/keyword-locations";
 import { formatMcpTable, type McpTableColumn } from "@/server/mcp/table";
+import { assertLanguageForLocation } from "@/server/lib/market";
 import {
-  DEFAULT_LANGUAGE_CODE,
-  DEFAULT_LOCATION_CODE,
-  assertLanguageForLocation,
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -108,13 +107,17 @@ export const researchKeywordsTool = {
     const results = await Promise.all(
       args.seeds.map(async (item) => {
         try {
-          assertLanguageForLocation(item.locationCode, item.languageCode);
+          const { locationCode, languageCode } = resolveMarket(
+            item,
+            context.project,
+          );
+          assertLanguageForLocation(locationCode, languageCode);
           const data = await KeywordResearchService.research(
             {
               projectId: args.projectId,
               keywords: [item.seed],
-              locationCode: item.locationCode ?? DEFAULT_LOCATION_CODE,
-              languageCode: item.languageCode ?? DEFAULT_LANGUAGE_CODE,
+              locationCode,
+              languageCode,
               resultLimit: args.resultLimit ?? 150,
               mode: "auto",
               clickstream: args.includeClickstreamData ?? false,
diff --git a/src/server/mcp/tools/save-keywords.ts b/src/server/mcp/tools/save-keywords.ts
index 65891af..defcab4 100644
--- a/src/server/mcp/tools/save-keywords.ts
+++ b/src/server/mcp/tools/save-keywords.ts
@@ -4,9 +4,8 @@ import { mcpResponse } from "@/server/mcp/formatters";
 import { buildProjectMeta } from "@/server/mcp/context";
 import { optionalMetaOutputSchema } from "@/server/mcp/output-schemas";
 import { withMcpProjectAuth } from "@/server/mcp/project-auth";
+import { resolveMarket } from "@/shared/keyword-locations";
 import {
-  DEFAULT_LANGUAGE_CODE,
-  DEFAULT_LOCATION_CODE,
   languageCodeSchema,
   locationCodeSchema,
   projectIdSchema,
@@ -66,8 +65,7 @@ export const saveKeywordsTool = {
       throw new Error("Replacement tags are required when tagMode is replace.");
     }
 
-    const locationCode = args.locationCode ?? DEFAULT_LOCATION_CODE;
-    const languageCode = args.languageCode ?? DEFAULT_LANGUAGE_CODE;
+    const { locationCode, languageCode } = resolveMarket(args, context.project);
 
     await KeywordResearchService.saveKeywords({
       projectId: args.projectId,
diff --git a/src/server/mcp/tools/saved-keywords-tools.test.ts b/src/server/mcp/tools/saved-keywords-tools.test.ts
index af1ee83..2632a00 100644
--- a/src/server/mcp/tools/saved-keywords-tools.test.ts
+++ b/src/server/mcp/tools/saved-keywords-tools.test.ts
@@ -51,7 +51,11 @@ describe("saved keyword MCP tools", () => {
   beforeEach(() => {
     vi.resetModules();
     mocks.getProjectForOrganization.mockReset();
-    mocks.getProjectForOrganization.mockResolvedValue({ id: "project_1" });
+    mocks.getProjectForOrganization.mockResolvedValue({
+      id: "project_1",
+      locationCode: 2840,
+      languageCode: "en",
+    });
     mocks.getSavedKeywords.mockReset();
     mocks.saveKeywords.mockReset();
   });
diff --git a/src/server/mcp/tools/search-console-tools.test.ts b/src/server/mcp/tools/search-console-tools.test.ts
index 8e080f6..7696ebb 100644
--- a/src/server/mcp/tools/search-console-tools.test.ts
+++ b/src/server/mcp/tools/search-console-tools.test.ts
@@ -76,7 +76,11 @@ const toolExtra: ToolExtra = {
 describe("search console MCP tools", () => {
   beforeEach(() => {
     mocks.getProjectForOrganization.mockReset();
-    mocks.getProjectForOrganization.mockResolvedValue({ id: "project_1" });
+    mocks.getProjectForOrganization.mockResolvedValue({
+      id: "project_1",
+      locationCode: 2840,
+      languageCode: "en",
+    });
     mocks.isHostedServerAuthMode.mockReset();
     mocks.isHostedServerAuthMode.mockResolvedValue(true);
     mocks.hasSelfHostedGscConfig.mockReset();
diff --git a/src/server/mcp/tools/tool-text-output.test.ts b/src/server/mcp/tools/tool-text-output.test.ts
index 6157a1f..ce9ea97 100644
--- a/src/server/mcp/tools/tool-text-output.test.ts
+++ b/src/server/mcp/tools/tool-text-output.test.ts
@@ -90,7 +90,11 @@ describe("MCP tool text output (service-backed tools)", () => {
   beforeEach(() => {
     vi.resetModules();
     for (const mock of Object.values(mocks)) mock.mockReset();
-    mocks.getProjectForOrganization.mockResolvedValue({ id: "project_1" });
+    mocks.getProjectForOrganization.mockResolvedValue({
+      id: "project_1",
+      locationCode: 2840,
+      languageCode: "en",
+    });
   });
 
   it("research_keywords renders every keyword row in the text table", async () => {
diff --git a/src/serverFunctions/domain.ts b/src/serverFunctions/domain.ts
index a9736c3..769cec1 100644
--- a/src/serverFunctions/domain.ts
+++ b/src/serverFunctions/domain.ts
@@ -7,6 +7,7 @@ import {
   domainPagesPageRequestSchema,
 } from "@/types/schemas/domain";
 import { DomainService } from "@/server/features/domain/services/DomainService";
+import { resolveLabsMarket } from "@/shared/keyword-locations";
 
 function shouldUseDomainE2eFixtures() {
   return import.meta.env.VITE_E2E_DOMAIN_FIXTURES === "1";
@@ -20,18 +21,17 @@ export const getDomainOverview = createServerFn({ method: "POST" })
   .middleware(requireProjectContext)
   .validator(domainOverviewSchema)
   .handler(async ({ data, context }) => {
+    const input = {
+      ...data,
+      ...resolveLabsMarket(data, context.project),
+      projectId: context.projectId,
+    };
     if (shouldUseDomainE2eFixtures()) {
       const fixtures = await getDomainE2eFixtures();
-      return fixtures.getFixtureOverview(data.domain);
+      return fixtures.getFixtureOverview(input.domain);
     }
 
-    return DomainService.getOverview(
-      {
-        ...data,
-        projectId: context.projectId,
-      },
-      context,
-    );
+    return DomainService.getOverview(input, context);
   });
 
 export const getDomainKeywordSuggestions = createServerFn({ method: "POST" })
@@ -41,6 +41,7 @@ export const getDomainKeywordSuggestions = createServerFn({ method: "POST" })
     DomainService.getSuggestedKeywords(
       {
         ...data,
+        ...resolveLabsMarket(data, context.project),
         organizationId: context.organizationId,
         projectId: context.projectId,
       },
@@ -52,34 +53,32 @@ export const getDomainKeywordsPage = createServerFn({ method: "POST" })
   .middleware(requireProjectContext)
   .validator(domainKeywordsPageRequestSchema)
   .handler(async ({ data, context }) => {
+    const input = {
+      ...data,
+      ...resolveLabsMarket(data, context.project),
+      projectId: context.projectId,
+    };
     if (shouldUseDomainE2eFixtures()) {
       const fixtures = await getDomainE2eFixtures();
-      return fixtures.getFixtureKeywordsPage(data);
+      return fixtures.getFixtureKeywordsPage(input);
     }
 
-    return DomainService.getKeywordsPage(
-      {
-        ...data,
-        projectId: context.projectId,
-      },
-      context,
-    );
+    return DomainService.getKeywordsPage(input, context);
   });
 
 export const getDomainPagesPage = createServerFn({ method: "POST" })
   .middleware(requireProjectContext)
   .validator(domainPagesPageRequestSchema)
   .handler(async ({ data, context }) => {
+    const input = {
+      ...data,
+      ...resolveLabsMarket(data, context.project),
+      projectId: context.projectId,
+    };
     if (shouldUseDomainE2eFixtures()) {
       const fixtures = await getDomainE2eFixtures();
-      return fixtures.getFixturePagesPage(data);
+      return fixtures.getFixturePagesPage(input);
     }
 
-    return DomainService.getPagesPage(
-      {
-        ...data,
-        projectId: context.projectId,
-      },
-      context,
-    );
+    return DomainService.getPagesPage(input, context);
   });
diff --git a/src/serverFunctions/keywords.ts b/src/serverFunctions/keywords.ts
index debccbb..293cbd4 100644
--- a/src/serverFunctions/keywords.ts
+++ b/src/serverFunctions/keywords.ts
@@ -13,6 +13,7 @@ import {
 } from "@/types/schemas/keywords";
 import { KeywordResearchService } from "@/server/features/keywords/services/KeywordResearchService";
 import { requireProjectContext } from "@/serverFunctions/middleware";
+import { resolveMarket } from "@/shared/keyword-locations";
 
 function shouldUseKeywordE2eFixtures() {
   return import.meta.env.VITE_E2E_KEYWORD_FIXTURES === "1";
@@ -26,18 +27,17 @@ export const researchKeywords = createServerFn({ method: "POST" })
   .middleware(requireProjectContext)
   .validator(researchKeywordsSchema)
   .handler(async ({ data, context }) => {
+    const input = {
+      ...data,
+      ...resolveMarket(data, context.project),
+      projectId: context.projectId,
+    };
     if (shouldUseKeywordE2eFixtures()) {
       const fixtures = await getKeywordE2eFixtures();
-      return fixtures.getKeywordResearchFixture(data);
+      return fixtures.getKeywordResearchFixture(input);
     }
 
-    return KeywordResearchService.research(
-      {
-        ...data,
-        projectId: context.projectId,
-      },
-      context,
-    );
+    return KeywordResearchService.research(input, context);
   });
 
 export const saveKeywords = createServerFn({ method: "POST" })
@@ -46,6 +46,7 @@ export const saveKeywords = createServerFn({ method: "POST" })
   .handler(async ({ data, context }) => {
     return KeywordResearchService.saveKeywords({
       ...data,
+      ...resolveMarket(data, context.project),
       projectId: context.projectId,
     });
   });
@@ -126,6 +127,7 @@ export const getSerpAnalysis = createServerFn({ method: "POST" })
     KeywordResearchService.getSerpAnalysis(
       {
         ...data,
+        ...resolveMarket(data, context.project),
         projectId: context.projectId,
       },
       context,
diff --git a/src/serverFunctions/projects.ts b/src/serverFunctions/projects.ts
index cc1032f..a8da794 100644
--- a/src/serverFunctions/projects.ts
+++ b/src/serverFunctions/projects.ts
@@ -8,6 +8,7 @@ import {
   archiveProjectSchema,
   createProjectSchema,
   restoreProjectSchema,
+  setProjectMarketSchema,
   updateProjectSchema,
 } from "@/types/schemas/projects";
 import { z } from "zod";
@@ -34,6 +35,13 @@ export const updateProject = createServerFn({ method: "POST" })
     ProjectService.updateProject(context.organizationId, data),
   );
 
+export const setProjectMarket = createServerFn({ method: "POST" })
+  .middleware(requireProjectContext)
+  .validator(setProjectMarketSchema)
+  .handler(async ({ data, context }) =>
+    ProjectService.setProjectMarket(context.organizationId, data),
+  );
+
 export const archiveProject = createServerFn({ method: "POST" })
   .middleware(requireProjectContext)
   .validator(archiveProjectSchema)
diff --git a/src/serverFunctions/rank-tracking.ts b/src/serverFunctions/rank-tracking.ts
index 40dc438..8f399a9 100644
--- a/src/serverFunctions/rank-tracking.ts
+++ b/src/serverFunctions/rank-tracking.ts
@@ -77,6 +77,7 @@ export const createRankTrackingConfig = createServerFn({ method: "POST" })
   .handler(async ({ data, context }) => {
     const result = await RankTrackingService.createConfig({
       projectId: context.projectId,
+      projectMarket: context.project,
       domain: data.domain,
       locationCode: data.locationCode,
       languageCode: data.languageCode,
diff --git a/src/shared/keyword-locations.test.ts b/src/shared/keyword-locations.test.ts
index c76d73c..0670ae1 100644
--- a/src/shared/keyword-locations.test.ts
+++ b/src/shared/keyword-locations.test.ts
@@ -9,6 +9,8 @@ import {
   isLabsLocationCode,
   isSupportedLanguageCode,
   isSupportedLocationCode,
+  resolveLabsMarket,
+  resolveMarket,
 } from "./keyword-locations";
 
 describe("keyword locations", () => {
@@ -94,3 +96,76 @@ describe("formatLocationLabel", () => {
     );
   });
 });
+
+describe("resolveMarket", () => {
+  const vietnamProject = { locationCode: 2704, languageCode: "vi" };
+
+  it("falls back to the project's pair when nothing is supplied", () => {
+    expect(resolveMarket({}, vietnamProject)).toEqual({
+      locationCode: 2704,
+      languageCode: "vi",
+    });
+  });
+
+  it("snaps the language to a location override instead of borrowing the project's", () => {
+    // A Vietnam project querying Germany must not send Vietnamese.
+    expect(resolveMarket({ locationCode: 2276 }, vietnamProject)).toEqual({
+      locationCode: 2276,
+      languageCode: "de",
+    });
+  });
+
+  it("keeps the project language when the override matches the project location", () => {
+    const spanishUs = { locationCode: 2840, languageCode: "es" };
+    expect(resolveMarket({ locationCode: 2840 }, spanishUs)).toEqual({
+      locationCode: 2840,
+      languageCode: "es",
+    });
+  });
+
+  it("applies an explicit language to the project's location", () => {
+    expect(resolveMarket({ languageCode: "en" }, vietnamProject)).toEqual({
+      locationCode: 2704,
+      languageCode: "en",
+    });
+  });
+
+  it("uses both overrides verbatim", () => {
+    expect(
+      resolveMarket({ locationCode: 2276, languageCode: "en" }, vietnamProject),
+    ).toEqual({ locationCode: 2276, languageCode: "en" });
+  });
+});
+
+describe("resolveLabsMarket", () => {
+  it("inherits a Labs-served project market like resolveMarket does", () => {
+    expect(
+      resolveLabsMarket({}, { locationCode: 2704, languageCode: "vi" }),
+    ).toEqual({ locationCode: 2704, languageCode: "vi" });
+  });
+
+  it("falls back to the US when the project market is Google-Ads-served", () => {
+    // Iceland has no Labs data. The caller never picked it, so a Labs-only
+    // tool must not fail on it.
+    expect(
+      resolveLabsMarket({}, { locationCode: 2352, languageCode: "en" }),
+    ).toEqual({ locationCode: 2840, languageCode: "en" });
+  });
+
+  it("falls back to the US when the project pair is not served", () => {
+    // Concurrent half-updates can leave a location/language pair Labs rejects;
+    // sending it would spend credits on a task that always fails.
+    expect(
+      resolveLabsMarket({}, { locationCode: 2276, languageCode: "vi" }),
+    ).toEqual({ locationCode: 2840, languageCode: "en" });
+  });
+
+  it("leaves an explicit location alone so the caller's assert can reject it", () => {
+    expect(
+      resolveLabsMarket(
+        { locationCode: 2352 },
+        { locationCode: 2704, languageCode: "vi" },
+      ),
+    ).toMatchObject({ locationCode: 2352 });
+  });
+});
diff --git a/src/shared/keyword-locations.ts b/src/shared/keyword-locations.ts
index 8412657..3a67472 100644
--- a/src/shared/keyword-locations.ts
+++ b/src/shared/keyword-locations.ts
@@ -697,6 +697,66 @@ export function getLanguageCode(locationCode: number): string {
   return LOCATION_LANGUAGE[locationCode] ?? "en";
 }
 
+/**
+ * Resolves a request's market against the project's default. The pair is
+ * resolved together: overriding only the location snaps the language to that
+ * location's default language, because the project's language was chosen for
+ * the project's own location and may not be valid — or sensible — for the
+ * override (e.g. a Vietnam project querying Germany must not default to
+ * Vietnamese).
+ */
+export function resolveMarket(
+  args: { locationCode?: number; languageCode?: string },
+  project: { locationCode: number; languageCode: string },
+): { locationCode: number; languageCode: string } {
+  const locationCode = args.locationCode ?? project.locationCode;
+  const languageCode =
+    args.languageCode ??
+    (locationCode === project.locationCode
+      ? project.languageCode
+      : getLanguageCode(locationCode));
+  return { locationCode, languageCode };
+}
+
+/**
+ * Whether DataForSEO serves this language for this location. Only Labs
+ * locations have authoritative per-location language lists; Google Ads
+ * locations are left to the metering safety net.
+ */
+export function isLanguageServedForLocation(
+  locationCode: number,
+  languageCode: string,
+): boolean {
+  if (getKeywordDataProvider(locationCode) !== "labs") return true;
+  return getLanguageOptions(locationCode).some(
+    (option) => option.code === languageCode,
+  );
+}
+
+/**
+ * Resolves the market for a Labs-only tool. Same as resolveMarket, except a
+ * project default Labs cannot serve is replaced by the United States: the
+ * caller never chose that market, so rejecting the call would dead-end on a
+ * value it can't see — and passing the pair through would spend credits on a
+ * task DataForSEO rejects. An explicit location is left alone, so a caller that
+ * names an unserved country still fails loudly on its own assert.
+ */
+export function resolveLabsMarket(
+  args: { locationCode?: number; languageCode?: string },
+  project: { locationCode: number; languageCode: string },
+): { locationCode: number; languageCode: string } {
+  const projectIsServed =
+    getKeywordDataProvider(project.locationCode) === "labs" &&
+    isLanguageServedForLocation(project.locationCode, project.languageCode);
+
+  return resolveMarket(
+    args,
+    projectIsServed
+      ? project
+      : { locationCode: DEFAULT_LOCATION_CODE, languageCode: "en" },
+  );
+}
+
 /**
  * Language codes DataForSEO accepts — the master LANGUAGE_OPTIONS list. Callers
  * (e.g. MCP tools) can pass an arbitrary `language_code`; an unsupported one is
@@ -738,9 +798,9 @@ const MULTI_LANGUAGE_LOCATIONS: Record<number, readonly string[]> = {
 };
 
 /**
- * Languages to offer for a location's rank-tracking config. Restricts the
- * global LANGUAGE_OPTIONS list to the languages DataForSEO supports for that
- * country, so the picker isn't a wall of irrelevant options.
+ * Languages to offer for a location. Restricts the global LANGUAGE_OPTIONS
+ * list to the languages DataForSEO supports for that country, so a picker
+ * isn't a wall of irrelevant options.
  */
 export function getLanguageOptions(
   locationCode: number,
diff --git a/src/shared/keyword-locations.vendor-defaults.test.ts b/src/shared/keyword-locations.vendor-defaults.test.ts
new file mode 100644
index 0000000..6deef7d
--- /dev/null
+++ b/src/shared/keyword-locations.vendor-defaults.test.ts
@@ -0,0 +1,147 @@
+import { describe, expect, it } from "vitest";
+import {
+  LABS_LOCATION_OPTIONS,
+  getLanguageCode,
+  isLabsLocationCode,
+} from "./keyword-locations";
+
+/**
+ * DataForSEO's own default language for each Labs location: the language with
+ * the most keyword records, which is what Labs uses when a call omits
+ * language_code. Snapshot of the free
+ * GET /v3/dataforseo_labs/locations_and_languages, taken 2026-07-16.
+ *
+ * LOCATION_LANGUAGE is hand-maintained, so it can drift from what DataForSEO
+ * actually serves — a drifted entry sends the wrong-language data for a
+ * country without failing. Refresh this snapshot with:
+ *
+ *   curl -s https://api.dataforseo.com/v3/dataforseo_labs/locations_and_languages \
+ *     -H "Authorization: Basic $DATAFORSEO_API_KEY" \
+ *   | jq -r '.tasks[0].result | sort_by(.location_code)[]
+ *       | "  \(.location_code): \"\(.available_languages | max_by(.keywords) | .language_code)\", // \(.location_name)"'
+ *
+ * Google-Ads-only countries are absent by design: Labs holds no data for them,
+ * so their language has no vendor answer to check against.
+ */
+const VENDOR_DEFAULT_LANGUAGE: Record<number, string> = {
+  2008: "sq", // Albania
+  2012: "fr", // Algeria
+  2024: "pt", // Angola
+  2031: "az", // Azerbaijan
+  2032: "es", // Argentina
+  2036: "en", // Australia
+  2040: "de", // Austria
+  2048: "ar", // Bahrain
+  2050: "bn", // Bangladesh
+  2051: "hy", // Armenia
+  2056: "nl", // Belgium
+  2068: "es", // Bolivia
+  2070: "bs", // Bosnia and Herzegovina
+  2076: "pt", // Brazil
+  2100: "bg", // Bulgaria
+  2104: "en", // Myanmar (Burma)
+  2116: "en", // Cambodia
+  2120: "fr", // Cameroon
+  2124: "en", // Canada
+  2144: "en", // Sri Lanka
+  2152: "es", // Chile
+  2158: "zh-TW", // Taiwan
+  2170: "es", // Colombia
+  2188: "es", // Costa Rica
+  2191: "hr", // Croatia
+  2196: "el", // Cyprus
+  2203: "cs", // Czechia
+  2208: "da", // Denmark
+  2218: "es", // Ecuador
+  2222: "es", // El Salvador
+  2233: "et", // Estonia
+  2246: "fi", // Finland
+  2250: "fr", // France
+  2276: "de", // Germany
+  2288: "en", // Ghana
+  2300: "el", // Greece
+  2320: "es", // Guatemala
+  2344: "zh-TW", // Hong Kong
+  2348: "hu", // Hungary
+  2356: "en", // India
+  2360: "id", // Indonesia
+  2372: "en", // Ireland
+  2376: "he", // Israel
+  2380: "it", // Italy
+  2384: "fr", // Cote d'Ivoire
+  2392: "ja", // Japan
+  2398: "ru", // Kazakhstan
+  2400: "ar", // Jordan
+  2404: "en", // Kenya
+  2410: "ko", // South Korea
+  2428: "lv", // Latvia
+  2440: "lt", // Lithuania
+  2458: "en", // Malaysia
+  2470: "en", // Malta
+  2484: "es", // Mexico
+  2492: "fr", // Monaco
+  2498: "ro", // Moldova
+  2504: "ar", // Morocco
+  2528: "nl", // Netherlands
+  2554: "en", // New Zealand
+  2558: "es", // Nicaragua
+  2566: "en", // Nigeria
+  2578: "nb", // Norway
+  2586: "en", // Pakistan
+  2591: "es", // Panama
+  2600: "es", // Paraguay
+  2604: "es", // Peru
+  2608: "en", // Philippines
+  2616: "pl", // Poland
+  2620: "pt", // Portugal
+  2642: "ro", // Romania
+  2682: "ar", // Saudi Arabia
+  2686: "fr", // Senegal
+  2688: "sr", // Serbia
+  2702: "en", // Singapore
+  2703: "sk", // Slovakia
+  2704: "vi", // Vietnam
+  2705: "sl", // Slovenia
+  2710: "en", // South Africa
+  2724: "es", // Spain
+  2752: "sv", // Sweden
+  2756: "de", // Switzerland
+  2764: "th", // Thailand
+  2784: "en", // United Arab Emirates
+  2788: "ar", // Tunisia
+  2792: "tr", // Turkiye
+  2804: "uk", // Ukraine
+  2807: "mk", // North Macedonia
+  2818: "ar", // Egypt
+  2826: "en", // United Kingdom
+  2840: "en", // United States
+  2854: "fr", // Burkina Faso
+  2858: "es", // Uruguay
+  2862: "es", // Venezuela
+};
+
+describe("getLanguageCode vs DataForSEO's Labs defaults", () => {
+  it("uses DataForSEO's default language for every Labs location", () => {
+    const drifted = Object.entries(VENDOR_DEFAULT_LANGUAGE)
+      .filter(([code, language]) => getLanguageCode(Number(code)) !== language)
+      .map(
+        ([code, language]) =>
+          `${code}: ours=${getLanguageCode(Number(code))} vendor=${language}`,
+      );
+    expect(drifted).toEqual([]);
+  });
+
+  it("classifies every location DataForSEO serves from Labs as a Labs location", () => {
+    const misclassified = Object.entries(VENDOR_DEFAULT_LANGUAGE)
+      .filter(([code]) => !isLabsLocationCode(Number(code)))
+      .map(([code, language]) => `${code}: vendor serves ${language} via Labs`);
+    expect(misclassified).toEqual([]);
+  });
+
+  it("covers every Labs location we offer, so a new one can't skip the check", () => {
+    const unverified = LABS_LOCATION_OPTIONS.filter(
+      (option) => VENDOR_DEFAULT_LANGUAGE[option.code] == null,
+    ).map((option) => `${option.code} ${option.label}`);
+    expect(unverified).toEqual([]);
+  });
+});
diff --git a/src/types/schemas/domain.ts b/src/types/schemas/domain.ts
index d967b50..c1e6db3 100644
--- a/src/types/schemas/domain.ts
+++ b/src/types/schemas/domain.ts
@@ -59,8 +59,8 @@ export const domainOverviewSchema = z.object({
   projectId: z.string().uuid(),
   domain: z.string().min(1, "Domain is required").max(255),
   includeSubdomains: z.boolean().default(true),
-  locationCode: z.number().int().positive().default(2840),
-  languageCode: z.string().min(2).max(8).default("en"),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
 });
 
 /* ------------------------------------------------------------------ */
@@ -74,8 +74,8 @@ const domainTabs = ["keywords", "pages"] as const;
 export const domainKeywordSuggestionsSchema = z.object({
   projectId: z.string().uuid(),
   domain: domainField,
-  locationCode: z.number().int().positive(),
-  languageCode: z.string().min(2).max(8),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
 });
 
 export const DOMAIN_KEYWORDS_PAGE_SIZES = [50, 100, 200] as const;
@@ -119,8 +119,8 @@ export const domainKeywordsPageRequestSchema = z.object({
   projectId: z.string().uuid(),
   domain: z.string().min(1).max(255),
   includeSubdomains: z.boolean().default(true),
-  locationCode: z.number().int().positive().default(2840),
-  languageCode: z.string().min(2).max(8).default("en"),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
   page: z.number().int().positive().default(1),
   pageSize: z
     .number()
@@ -141,8 +141,8 @@ export const domainPagesPageRequestSchema = z.object({
   projectId: z.string().uuid(),
   domain: z.string().min(1).max(255),
   includeSubdomains: z.boolean().default(true),
-  locationCode: z.number().int().positive().default(2840),
-  languageCode: z.string().min(2).max(8).default("en"),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
   page: z.number().int().positive().default(1),
   pageSize: z
     .number()
diff --git a/src/types/schemas/keywords.ts b/src/types/schemas/keywords.ts
index 303d377..2a1af9c 100644
--- a/src/types/schemas/keywords.ts
+++ b/src/types/schemas/keywords.ts
@@ -18,8 +18,8 @@ const sortDirs = ["asc", "desc"] as const;
 export const researchKeywordsSchema = z.object({
   projectId: z.string().min(1),
   keywords: z.array(z.string().min(1)).min(1).max(200),
-  locationCode: z.number().int().positive().default(2840),
-  languageCode: z.string().min(2).max(8).default("en"),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
   resultLimit: z
     .union([z.literal(150), z.literal(300), z.literal(500)])
     .default(150),
@@ -35,8 +35,8 @@ export const saveKeywordsSchema = z
   .object({
     projectId: z.string().min(1),
     keywords: z.array(z.string().min(1)).min(1).max(500),
-    locationCode: z.number().int().positive().default(2840),
-    languageCode: z.string().min(2).max(8).default("en"),
+    locationCode: z.number().int().positive().optional(),
+    languageCode: z.string().min(2).max(8).optional(),
     tags: z.array(savedKeywordTagSchema).max(20).optional(),
     tagMode: z.enum(["append", "replace"]).optional(),
     metrics: z
@@ -149,6 +149,17 @@ export const refreshSavedKeywordMetricsSchema = z.object({
 
 export type ResearchKeywordsInput = z.infer<typeof researchKeywordsSchema>;
 export type SaveKeywordsInput = z.infer<typeof saveKeywordsSchema>;
+type ResolvedMarket = { locationCode: number; languageCode: string };
+export type ResolvedResearchKeywordsInput = Omit<
+  ResearchKeywordsInput,
+  keyof ResolvedMarket
+> &
+  ResolvedMarket;
+export type ResolvedSaveKeywordsInput = Omit<
+  SaveKeywordsInput,
+  keyof ResolvedMarket
+> &
+  ResolvedMarket;
 export type RemoveSavedKeywordsInput = z.infer<
   typeof removeSavedKeywordsSchema
 >;
@@ -172,8 +183,8 @@ export type RefreshSavedKeywordMetricsInput = z.infer<
 export const serpAnalysisSchema = z.object({
   projectId: z.string().min(1),
   keyword: z.string().min(1),
-  locationCode: z.number().int().positive().default(2840),
-  languageCode: z.string().min(2).max(8).default("en"),
+  locationCode: z.number().int().positive().optional(),
+  languageCode: z.string().min(2).max(8).optional(),
 });
 
 /* ------------------------------------------------------------------ */
diff --git a/src/types/schemas/projects.test.ts b/src/types/schemas/projects.test.ts
new file mode 100644
index 0000000..f7ff01b
--- /dev/null
+++ b/src/types/schemas/projects.test.ts
@@ -0,0 +1,39 @@
+import { describe, expect, it } from "vitest";
+import { createProjectSchema, updateProjectSchema } from "./projects";
+
+// The service derives a missing language from the location, so a language
+// arriving on its own has nothing to validate against.
+describe("project market fields", () => {
+  it("rejects a language with no location", () => {
+    expect(
+      updateProjectSchema.safeParse({
+        projectId: "project_1",
+        name: "Acme",
+        languageCode: "vi",
+      }).success,
+    ).toBe(false);
+    expect(
+      createProjectSchema.safeParse({ name: "Acme", languageCode: "vi" })
+        .success,
+    ).toBe(false);
+  });
+
+  it("accepts a location on its own, and a full pair", () => {
+    expect(
+      createProjectSchema.safeParse({ name: "Acme", locationCode: 2704 })
+        .success,
+    ).toBe(true);
+    expect(
+      updateProjectSchema.safeParse({
+        projectId: "project_1",
+        name: "Acme",
+        locationCode: 2704,
+        languageCode: "vi",
+      }).success,
+    ).toBe(true);
+  });
+
+  it("accepts a project with no market at all", () => {
+    expect(createProjectSchema.safeParse({ name: "Acme" }).success).toBe(true);
+  });
+});
diff --git a/src/types/schemas/projects.ts b/src/types/schemas/projects.ts
index 8afb457..98180a1 100644
--- a/src/types/schemas/projects.ts
+++ b/src/types/schemas/projects.ts
@@ -1,4 +1,8 @@
 import { z } from "zod";
+import {
+  isSupportedLanguageCode,
+  isSupportedLocationCode,
+} from "@/shared/keyword-locations";
 
 const projectNameField = z
   .string()
@@ -13,15 +17,63 @@ const projectDomainField = z
   .transform((value) => value || undefined)
   .optional();
 
-export const createProjectSchema = z.object({
-  name: projectNameField,
-  domain: projectDomainField,
-});
+// Default market for the project's data calls. The location/language PAIR is
+// validated in the service (an update may change one side and needs the
+// stored row for the other).
+const projectLocationCodeField = z
+  .number()
+  .int()
+  .refine(isSupportedLocationCode, "Unsupported DataForSEO location code")
+  .optional();
 
-export const updateProjectSchema = z.object({
+const projectLanguageCodeField = z
+  .string()
+  .refine(isSupportedLanguageCode, "Unsupported language code")
+  .optional();
+
+// A language on its own has no location to validate against, and would force a
+// read of the stored row to resolve. Callers set the market as a pair, or send
+// a location alone and let the service derive its language.
+const hasLocationForLanguage = (input: {
+  locationCode?: number;
+  languageCode?: string;
+}) => input.locationCode != null || input.languageCode == null;
+
+const marketPairMessage = {
+  message: "A language requires a location.",
+  path: ["languageCode"],
+};
+
+export const createProjectSchema = z
+  .object({
+    name: projectNameField,
+    domain: projectDomainField,
+    locationCode: projectLocationCodeField,
+    languageCode: projectLanguageCodeField,
+  })
+  .refine(hasLocationForLanguage, marketPairMessage);
+
+export const updateProjectSchema = z
+  .object({
+    projectId: z.string().min(1),
+    name: projectNameField,
+    domain: projectDomainField,
+    locationCode: projectLocationCodeField,
+    languageCode: projectLanguageCodeField,
+  })
+  .refine(hasLocationForLanguage, marketPairMessage);
+
+// Market-only update (onboarding). Both halves are required: the caller picks
+// them together, so the service can validate the pair without a stored row.
+export const setProjectMarketSchema = z.object({
   projectId: z.string().min(1),
-  name: projectNameField,
-  domain: projectDomainField,
+  locationCode: z
+    .number()
+    .int()
+    .refine(isSupportedLocationCode, "Unsupported DataForSEO location code"),
+  languageCode: z
+    .string()
+    .refine(isSupportedLanguageCode, "Unsupported language code"),
 });
 
 export const archiveProjectSchema = z.object({
@@ -37,5 +89,6 @@ export const restoreProjectSchema = z.object({
 
 export type CreateProjectInput = z.infer<typeof createProjectSchema>;
 export type UpdateProjectInput = z.infer<typeof updateProjectSchema>;
+export type SetProjectMarketInput = z.infer<typeof setProjectMarketSchema>;
 export type ArchiveProjectInput = z.infer<typeof archiveProjectSchema>;
 export type RestoreProjectInput = z.infer<typeof restoreProjectSchema>;