diff --git a/e2e/tests/device-ratio.spec.ts b/e2e/tests/device-ratio.spec.ts
new file mode 100644
index 0000000..df82793
--- /dev/null
+++ b/e2e/tests/device-ratio.spec.ts
@@ -0,0 +1,23 @@
+import { test, expect } from "@playwright/test";
+
+const USERNAME = process.env.LOCAL_USERNAME ?? "admin";
+const PASSWORD = process.env.LOCAL_PASSWORD ?? "";
+
+test("known/unknown ratio matches the actual badge counts", 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 });
+
+  const knownCount = await page.locator(".device-badge.known").count();
+  const unknownCount = await page.locator(".device-badge.unknown").count();
+
+  const ratioText = await page.locator(".device-ratio").textContent();
+  expect(ratioText).toBe(`${knownCount} known / ${unknownCount} unknown`);
+
+  const countText = await page.locator(".device-count").textContent();
+  expect(countText).toBe(`(${knownCount + unknownCount})`);
+});