diff --git a/e2e/tests/new-device-badge.spec.ts b/e2e/tests/new-device-badge.spec.ts
new file mode 100644
index 0000000..27eddf5
--- /dev/null
+++ b/e2e/tests/new-device-badge.spec.ts
@@ -0,0 +1,28 @@
+import { test, expect } from "@playwright/test";
+
+const USERNAME = process.env.LOCAL_USERNAME ?? "admin";
+const PASSWORD = process.env.LOCAL_PASSWORD ?? "";
+
+test("'new' badge count matches the API's isNew count", async ({ page }) => {
+  test.skip(!PASSWORD, "LOCAL_PASSWORD not set");
+
+  await page.goto("/");
+  await page.getByPlaceholder("Username").fill(USERNAME);
+  await page.getByPlaceholder("Password").fill(PASSWORD);
+  await page.getByRole("button", { name: "Sign in" }).click();
+  await expect(page.locator(".device-table tbody tr").first()).toBeVisible({ timeout: 15_000 });
+
+  // Cross-check against the API directly rather than forcing a synthetic
+  // "new device" scenario -- that would permanently pollute the production
+  // seen_macs table on every test run. Whatever's genuinely new right now is
+  // enough to verify the UI reflects the API correctly. page.request (not
+  // the bare `request` fixture) shares the browser context's session cookie.
+  const res = await page.request.get("/api/devices");
+  const { devices } = await res.json();
+  const apiNewCount = devices.filter((d: { isNew: boolean }) => d.isNew).length;
+
+  await expect(async () => {
+    const badgeCount = await page.locator(".device-badge.new").count();
+    expect(badgeCount).toBe(apiNewCount);
+  }).toPass({ timeout: 10_000 });
+});