diff --git a/internal/driver/chrome/translate.go b/internal/driver/chrome/translate.go
index 561e09f..091c0a7 100644
--- a/internal/driver/chrome/translate.go
+++ b/internal/driver/chrome/translate.go
@@ -42,7 +42,13 @@ func TranslateStringSelector(selector string) (string, bool, error) {
 		return `[aria-label="` + cssEscape(value) + `"]`, false, nil
 	case "descPrefix":
 		return `[aria-label^="` + cssEscape(value) + `"]`, false, nil
-	case "testTag", "testID", "testid", "data-testid":
+	case "testTag":
+		// Mirrors the in-page table and the native resource-id alias: a
+		// testTag reaches the DOM as data-testid or as an id, depending on
+		// the toolkit. `:is()` keeps this one compound selector.
+		escaped := cssEscape(value)
+		return `:is([data-testid="` + escaped + `"], [id="` + escaped + `"])`, false, nil
+	case "testID", "testid", "data-testid":
 		return `[data-testid="` + cssEscape(value) + `"]`, false, nil
 	case "placeholder", "placeholderValue", "hintText":
 		return `[placeholder="` + cssEscape(value) + `"]`, false, nil
diff --git a/internal/driver/chrome/translate_test.go b/internal/driver/chrome/translate_test.go
index f89be06..79b6931 100644
--- a/internal/driver/chrome/translate_test.go
+++ b/internal/driver/chrome/translate_test.go
@@ -21,7 +21,7 @@ func TestTranslateStringSelector_KnownKeys(t *testing.T) {
 		{"accessibilityLabel:logout", `[aria-label="logout"]`, false},
 		{"aria-label:Sign in", `[aria-label="Sign in"]`, false},
 		{"descPrefix:account:", `[aria-label^="account:"]`, false},
-		{"testTag:submit", `[data-testid="submit"]`, false},
+		{"testTag:submit", `:is([data-testid="submit"], [id="submit"])`, false},
 		{"testID:submit", `[data-testid="submit"]`, false},
 		{"placeholder:Email", `[placeholder="Email"]`, false},
 	}
diff --git a/pkg/spec/src/web-runtime.ts b/pkg/spec/src/web-runtime.ts
index ca84236..ae3356a 100644
--- a/pkg/spec/src/web-runtime.ts
+++ b/pkg/spec/src/web-runtime.ts
@@ -85,7 +85,12 @@ function noopFormula(): unknown {
 const KNOWN_KEY_TO_CSS: Record<string, (value: string) => string> = {
   id: (v) => `[id="${cssEscape(v)}"]`,
   "resource-id": (v) => `[id="${cssEscape(v)}"]`,
-  testTag: (v) => `[data-testid="${cssEscape(v)}"]`,
+  // The native table aliases testTag onto resource-id, which the host DOM walk
+  // fills from el.id, so the native path already accepts a testTag emitted as
+  // an id (what Compose Multiplatform does on web). Accept both here so the
+  // tables agree. `:is()` keeps this one compound, since a multi-key selector
+  // concatenates the parts.
+  testTag: (v) => `:is([data-testid="${cssEscape(v)}"], [id="${cssEscape(v)}"])`,
   testID: (v) => `[data-testid="${cssEscape(v)}"]`,
   "data-testid": (v) => `[data-testid="${cssEscape(v)}"]`,
   className: (v) => `[class~="${cssEscape(v)}"]`,
diff --git a/pkg/spec/test/web-runtime.test.ts b/pkg/spec/test/web-runtime.test.ts
index 5703719..70c1160 100644
--- a/pkg/spec/test/web-runtime.test.ts
+++ b/pkg/spec/test/web-runtime.test.ts
@@ -310,6 +310,23 @@ test("selectorFromObject maps known keys to their canonical attribute", () => {
   });
 });
 
+// Compose Multiplatform emits its testTag into `id`, which the native table
+// already accepts via the resource-id alias. The web table must not be the one
+// place that rejects it.
+test("selectorFromObject resolves testTag through data-testid or id", () => {
+  assert.deepEqual(selectorFromObject({ testTag: "LoginSubmit" }), {
+    css: `:is([data-testid="LoginSubmit"], [id="LoginSubmit"])`,
+  });
+});
+
+// Multi-key selectors concatenate their parts into one compound, so the
+// two-attribute testTag match has to stay a single compound piece.
+test("selectorFromObject composes testTag with a second key", () => {
+  assert.deepEqual(selectorFromObject({ testTag: "Row", "aria-label": "first" }), {
+    css: `:is([data-testid="Row"], [id="Row"])[aria-label="first"]`,
+  });
+});
+
 test("selectorFromObject falls back to a literal attribute for unknown keys", () => {
   assert.deepEqual(selectorFromObject({ "data-foo": "bar" }), {
     css: `[data-foo="bar"]`,