diff --git a/apps/web/src/components/DeviceTable.tsx b/apps/web/src/components/DeviceTable.tsx
index f370f2f..94b5c0f 100644
--- a/apps/web/src/components/DeviceTable.tsx
+++ b/apps/web/src/components/DeviceTable.tsx
@@ -133,7 +133,7 @@ export function DeviceTable({
       </thead>
       <tbody>
         {sorted.map((d) => (
-          <tr key={d.ip}>
+          <tr key={d.ip} data-ip={d.ip}>
             <td>
               <span className={`device-badge ${d.known ? "known" : "unknown"}`}>
                 {d.known ? "known" : "unknown"}
diff --git a/e2e/tests/device-labeling.spec.ts b/e2e/tests/device-labeling.spec.ts
new file mode 100644
index 0000000..2d7e8bf
--- /dev/null
+++ b/e2e/tests/device-labeling.spec.ts
@@ -0,0 +1,38 @@
+import { test, expect } from "@playwright/test";
+
+const USERNAME = process.env.LOCAL_USERNAME ?? "admin";
+const PASSWORD = process.env.LOCAL_PASSWORD ?? "";
+
+test("labeling an unknown device makes it known, clearing reverts it", async ({ page }) => {
+  test.skip(!PASSWORD, "LOCAL_PASSWORD not set");
+
+  await page.goto("/");
+  await page.getByPlaceholder("Username").fill(USERNAME);
+  await page.getByPlaceholder("Password").fill(PASSWORD);
+  await page.getByRole("button", { name: "Sign in" }).click();
+  await expect(page.locator(".device-table tbody tr").first()).toBeVisible({ timeout: 15_000 });
+
+  const unknownRow = page.locator(".device-table tbody tr").filter({ hasText: "unknown" }).first();
+  await expect(unknownRow).toBeVisible();
+  const ip = await unknownRow.getAttribute("data-ip");
+
+  // Exact match via data-ip, not text -- an IP like 192.168.1.1 is a
+  // substring of 192.168.1.100/117/171/etc, so text-based row filtering is
+  // not reliable here (caught this the hard way on the first run).
+  const row = page.locator(`tr[data-ip="${ip}"]`);
+
+  await row.locator(".name-cell").click();
+  await row.getByPlaceholder("Label this device").fill("Playwright test label");
+  await row.getByRole("button", { name: "Save" }).click();
+
+  await expect(row.locator(".device-badge")).toHaveText("known");
+  await expect(row).toContainText("Playwright test label");
+
+  // Clear it back out so the test doesn't leave permanent residue on a real device.
+  await row.locator(".name-cell").click();
+  await row.getByPlaceholder("Label this device").fill("");
+  await row.getByRole("button", { name: "Save" }).click();
+
+  await expect(row.locator(".device-badge")).toHaveText("unknown");
+  await expect(row).not.toContainText("Playwright test label");
+});