diff --git a/Auto Run Docs/SpecKit-web-header-analyzer-Phase-04-Test-Selection.md b/Auto Run Docs/SpecKit-web-header-analyzer-Phase-04-Test-Selection.md
index d07f955..ca5b53e 100644
--- a/Auto Run Docs/SpecKit-web-header-analyzer-Phase-04-Test-Selection.md	
+++ b/Auto Run Docs/SpecKit-web-header-analyzer-Phase-04-Test-Selection.md	
@@ -21,7 +21,7 @@ This phase implements the test selection panel and analysis configuration contro
 ## Tasks
 
 - [x] T020 [US2] Write failing test (TDD Red) in `backend/tests/api/test_tests_router.py` — verify `GET /api/tests` returns 200 with all registered test IDs and names. Use httpx AsyncClient against the FastAPI test app
-- [ ] T021 [US2] Create `backend/app/schemas/tests.py` (response schema) and `backend/app/routers/tests.py` — FastAPI router with `GET /api/tests` returning all available tests (id, name, category) from scanner registry. Register router in `backend/app/main.py`. Verify `test_tests_router.py` passes (TDD Green)
+- [x] T021 [US2] Create `backend/app/schemas/tests.py` (response schema) and `backend/app/routers/tests.py` — FastAPI router with `GET /api/tests` returning all available tests (id, name, category) from scanner registry. Register router in `backend/app/main.py`. Verify `test_tests_router.py` passes (TDD Green)
 - [ ] T022 [US2] Write failing tests (TDD Red) in `frontend/src/__tests__/TestSelector.test.tsx` (render with mocked list, select/deselect all, search filtering) and `frontend/src/__tests__/AnalysisControls.test.tsx` (render, toggle states, keyboard accessibility)
 - [ ] T023 [P] [US2] Create `frontend/src/components/TestSelector.tsx` — dropdown with checkboxes per test, fetches list from `GET /api/tests`, "Select All"/"Deselect All" buttons (FR-04), text search/filter (FR-23), grouped by vendor/category (FR-24), FontAwesome icons. Verify `TestSelector.test.tsx` passes (TDD Green)
 - [ ] T024 [P] [US2] Create `frontend/src/components/AnalysisControls.tsx` — panel containing TestSelector, DNS resolution toggle (off by default, FR-18), decode-all toggle (FR-19), FontAwesome toggle icons, keyboard accessible (NFR-02). Verify `AnalysisControls.test.tsx` passes (TDD Green)
diff --git a/backend/app/main.py b/backend/app/main.py
index 9b3db6f..94e3714 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -1,6 +1,9 @@
 from fastapi import FastAPI
 
+from app.routers.tests import router as tests_router
+
 app = FastAPI(title="Web Header Analyzer API")
+app.include_router(tests_router)
 
 
 @app.get("/")
diff --git a/backend/app/routers/__init__.py b/backend/app/routers/__init__.py
new file mode 100644
index 0000000..c5cfac8
--- /dev/null
+++ b/backend/app/routers/__init__.py
@@ -0,0 +1 @@
+"""FastAPI routers."""
diff --git a/backend/app/routers/tests.py b/backend/app/routers/tests.py
new file mode 100644
index 0000000..cee004e
--- /dev/null
+++ b/backend/app/routers/tests.py
@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+from fastapi import APIRouter
+
+from app.engine.scanner_registry import ScannerRegistry
+from app.schemas.tests import TestResponse
+
+router = APIRouter(prefix="/api", tags=["tests"])
+
+
+@router.get("/tests", response_model=list[TestResponse])
+def list_tests() -> list[TestResponse]:
+    registry = ScannerRegistry()
+    tests = registry.list_tests()
+    return [TestResponse.model_validate(test) for test in tests]
diff --git a/backend/app/schemas/__init__.py b/backend/app/schemas/__init__.py
new file mode 100644
index 0000000..3fea1a0
--- /dev/null
+++ b/backend/app/schemas/__init__.py
@@ -0,0 +1 @@
+"""API response schemas."""
diff --git a/backend/app/schemas/tests.py b/backend/app/schemas/tests.py
new file mode 100644
index 0000000..cb29e69
--- /dev/null
+++ b/backend/app/schemas/tests.py
@@ -0,0 +1,7 @@
+from __future__ import annotations
+
+from app.engine.models import Test
+
+
+class TestResponse(Test):
+    pass