diff --git a/backend/tests/health.test.ts b/backend/tests/health.test.ts
index 7d97973a..76704dd6 100644
--- a/backend/tests/health.test.ts
+++ b/backend/tests/health.test.ts
@@ -97,4 +97,75 @@ describe('GET /health', () => {
     expect(typeof res.body.indexerLag).toBe('number');
     expect(typeof res.body.uptime).toBe('number');
   });
+
+  describe('response shape contract assertions', () => {
+    const EXPECTED_HEALTH_KEYS = ['db', 'indexerEnabled', 'indexerLag', 'status', 'uptime'];
+
+    it('matches exact response shape contract in healthy state (200 OK)', async () => {
+      vi.stubEnv('STREAM_CONTRACT_ID', 'CSOME_CONTRACT_ADDRESS');
+      prismaMock.indexerState.findUnique.mockResolvedValue(makeState(15));
+
+      const res = await request(app).get('/health');
+      expect(res.status).toBe(200);
+
+      // Verify exact keys set
+      expect(Object.keys(res.body).sort()).toEqual(EXPECTED_HEALTH_KEYS);
+
+      // Verify type & contract values
+      expect(res.body).toEqual({
+        status: 'ok',
+        db: 'connected',
+        indexerEnabled: true,
+        indexerLag: expect.any(Number),
+        uptime: expect.any(Number),
+      });
+      expect(res.body.indexerLag).toBe(15);
+      expect(res.body.uptime).toBeGreaterThanOrEqual(0);
+    });
+
+    it('matches exact response shape contract in degraded state (indexer lagging > 60s -> 503)', async () => {
+      vi.stubEnv('STREAM_CONTRACT_ID', 'CSOME_CONTRACT_ADDRESS');
+      prismaMock.indexerState.findUnique.mockResolvedValue(makeState(120));
+
+      const res = await request(app).get('/health');
+      expect(res.status).toBe(503);
+
+      // Verify exact keys set
+      expect(Object.keys(res.body).sort()).toEqual(EXPECTED_HEALTH_KEYS);
+
+      // Verify type & contract values
+      expect(res.body).toEqual({
+        status: 'degraded',
+        db: 'connected',
+        indexerEnabled: true,
+        indexerLag: expect.any(Number),
+        uptime: expect.any(Number),
+      });
+      expect(res.body.indexerLag).toBe(120);
+      expect(res.body.uptime).toBeGreaterThanOrEqual(0);
+    });
+
+    it('matches exact response shape contract in degraded state (DB disconnected -> 503)', async () => {
+      vi.stubEnv('STREAM_CONTRACT_ID', 'CSOME_CONTRACT_ADDRESS');
+      prismaMock.$queryRaw.mockRejectedValue(new Error('DB Connection Error'));
+      prismaMock.indexerState.findUnique.mockResolvedValue(makeState(5));
+
+      const res = await request(app).get('/health');
+      expect(res.status).toBe(503);
+
+      // Verify exact keys set
+      expect(Object.keys(res.body).sort()).toEqual(EXPECTED_HEALTH_KEYS);
+
+      // Verify type & contract values
+      expect(res.body).toEqual({
+        status: 'degraded',
+        db: 'disconnected',
+        indexerEnabled: true,
+        indexerLag: 5,
+        uptime: expect.any(Number),
+      });
+      expect(res.body.uptime).toBeGreaterThanOrEqual(0);
+    });
+  });
 });
+