diff --git a/src/server/routes/health.test.ts b/src/server/routes/health.test.ts
new file mode 100644
index 00000000..14c12361
--- /dev/null
+++ b/src/server/routes/health.test.ts
@@ -0,0 +1,143 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { healthMiddleware } from "./health.js";
+import type { ApiClient } from "@/shared/api/client.js";
+
+function createMockApiClient(
+  behavior: "ok" | "error" | "timeout" = "ok",
+): ApiClient {
+  const client = {
+    get: vi.fn(),
+    post: vi.fn(),
+  } as unknown as ApiClient;
+
+  if (behavior === "ok") {
+    vi.mocked(client.get).mockResolvedValue({ status: "ok" });
+  } else if (behavior === "error") {
+    vi.mocked(client.get).mockRejectedValue(new Error("upstream down"));
+  } else {
+    vi.mocked(client.get).mockImplementation(
+      () => new Promise(() => {}), // never resolves
+    );
+  }
+
+  return client;
+}
+
+function createMockRes() {
+  const res = {
+    statusCode: 200,
+    status: vi.fn().mockReturnThis(),
+    json: vi.fn().mockReturnThis(),
+    setHeader: vi.fn(),
+  };
+  return res;
+}
+
+describe("healthMiddleware", () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  it("returns 200 when upstream is reachable", async () => {
+    const apiClient = createMockApiClient("ok");
+    const handler = healthMiddleware({ apiClient });
+
+    const req = {} as any;
+    const res = createMockRes();
+    const next = vi.fn();
+
+    await handler(req, res as any, next);
+
+    expect(res.status).toHaveBeenCalledWith(200);
+    expect(res.json).toHaveBeenCalledWith({ status: "ok" });
+  });
+
+  it("returns 503 when upstream ping fails", async () => {
+    const apiClient = createMockApiClient("error");
+    const handler = healthMiddleware({ apiClient });
+
+    const req = {} as any;
+    const res = createMockRes();
+    const next = vi.fn();
+
+    await handler(req, res as any, next);
+
+    expect(res.status).toHaveBeenCalledWith(503);
+    expect(res.json).toHaveBeenCalledWith({
+      status: "degraded",
+      reason: "upstream_unreachable",
+    });
+  });
+
+  it("returns 200 if last success is within 60s even if current ping fails", async () => {
+    const apiClient = createMockApiClient("ok");
+    const handler = healthMiddleware({ apiClient });
+
+    const req = {} as any;
+    const res1 = createMockRes();
+    await handler(req, res1 as any, vi.fn());
+    expect(res1.status).toHaveBeenCalledWith(200);
+
+    // Now make it fail
+    vi.mocked(apiClient.get).mockRejectedValue(new Error("fail"));
+
+    // Advance 30s — still within 60s window
+    vi.advanceTimersByTime(30_000);
+
+    const res2 = createMockRes();
+    await handler(req, res2 as any, vi.fn());
+    expect(res2.status).toHaveBeenCalledWith(200);
+  });
+
+  it("returns 503 if last success is older than 60s", async () => {
+    const apiClient = createMockApiClient("ok");
+    const handler = healthMiddleware({ apiClient });
+
+    const req = {} as any;
+    const res1 = createMockRes();
+    await handler(req, res1 as any, vi.fn());
+    expect(res1.status).toHaveBeenCalledWith(200);
+
+    // Now make it fail
+    vi.mocked(apiClient.get).mockRejectedValue(new Error("fail"));
+
+    // Advance 61s — beyond 60s window
+    vi.advanceTimersByTime(61_000);
+
+    const res2 = createMockRes();
+    await handler(req, res2 as any, vi.fn());
+    expect(res2.status).toHaveBeenCalledWith(503);
+  });
+
+  it("respects custom upstreamTimeoutMs", async () => {
+    const apiClient = createMockApiClient("timeout");
+    const handler = healthMiddleware({
+      apiClient,
+      upstreamTimeoutMs: 100,
+    });
+
+    const req = {} as any;
+    const res = createMockRes();
+    const next = vi.fn();
+
+    // The handler should abort the ping after 100ms
+    const promise = handler(req, res as any, next);
+    vi.advanceTimersByTime(200);
+    await promise;
+
+    expect(res.status).toHaveBeenCalledWith(503);
+  });
+
+  it("does not call next — health is a terminal response", async () => {
+    const apiClient = createMockApiClient("ok");
+    const handler = healthMiddleware({ apiClient });
+
+    const req = {} as any;
+    const res = createMockRes();
+    const next = vi.fn();
+
+    await handler(req, res as any, next);
+
+    expect(next).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/server/routes/health.ts b/src/server/routes/health.ts
new file mode 100644
index 00000000..2fbc92c1
--- /dev/null
+++ b/src/server/routes/health.ts
@@ -0,0 +1,60 @@
+import type { ApiClient } from "@/shared/api/client.js";
+import type { IncomingMessage, ServerResponse } from "node:http";
+
+export interface HealthMiddlewareOptions {
+  apiClient: ApiClient;
+  upstreamTimeoutMs?: number;
+}
+
+const STALE_THRESHOLD_MS = 60_000;
+const DEFAULT_UPSTREAM_TIMEOUT_MS = 5_000;
+
+/**
+ * Factory that creates a health-check handler. Returns 200 if the last
+ * successful upstream ping is within 60 s, 503 otherwise.
+ *
+ * This is an Express-style `(req, res, next)` handler — it does NOT
+ * auto-register itself as Modern.js middleware. Registration happens
+ * in a future integration step.
+ */
+export function healthMiddleware(options: HealthMiddlewareOptions) {
+  const { apiClient, upstreamTimeoutMs = DEFAULT_UPSTREAM_TIMEOUT_MS } =
+    options;
+
+  let lastSuccessTs = 0;
+
+  return async (
+    _req: IncomingMessage,
+    res: ServerResponse & {
+      status: (code: number) => ServerResponse;
+      json: (body: unknown) => void;
+    },
+    _next: () => void,
+  ): Promise<void> => {
+    // Attempt to ping the upstream API
+    try {
+      await Promise.race([
+        apiClient.get("/health"),
+        new Promise<never>((_resolve, reject) =>
+          setTimeout(
+            () => reject(new Error("upstream_timeout")),
+            upstreamTimeoutMs,
+          ),
+        ),
+      ]);
+      lastSuccessTs = Date.now();
+    } catch {
+      // ping failed — rely on cached lastSuccessTs
+    }
+
+    const age = Date.now() - lastSuccessTs;
+
+    if (lastSuccessTs > 0 && age < STALE_THRESHOLD_MS) {
+      res.status(200).json({ status: "ok" });
+    } else {
+      res
+        .status(503)
+        .json({ status: "degraded", reason: "upstream_unreachable" });
+    }
+  };
+}