diff --git a/app/docs/route.test.ts b/app/docs/route.test.ts
new file mode 100644
index 0000000..e849edc
--- /dev/null
+++ b/app/docs/route.test.ts
@@ -0,0 +1,32 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const mocks = vi.hoisted(() => ({
+  getSession: vi.fn(),
+  listDocs: vi.fn(),
+  listSharedDocs: vi.fn(),
+}));
+
+vi.mock("@/lib/auth/session", () => ({ getSession: mocks.getSession }));
+vi.mock("@/lib/docs/store", () => ({
+  listDocs: mocks.listDocs,
+  listSharedDocs: mocks.listSharedDocs,
+}));
+vi.mock("@/lib/db", () => ({ query: vi.fn() }));
+
+import { GET } from "@/app/docs/route";
+
+describe("GET /docs", () => {
+  beforeEach(() => {
+    mocks.getSession.mockResolvedValue({ id: 1, email: "user@example.com", user_id: 1 });
+    mocks.listDocs.mockResolvedValue([]);
+    mocks.listSharedDocs.mockResolvedValue([]);
+  });
+
+  it("shows a logout button for the current session", async () => {
+    const res = await GET(new Request("https://justhtml.sh/docs"));
+    const html = await res.text();
+
+    expect(html).toContain('<form method="POST" action="/logout">');
+    expect(html).toContain('<button type="submit">log out</button>');
+  });
+});
diff --git a/app/docs/route.ts b/app/docs/route.ts
index d49ab10..5e8359b 100644
--- a/app/docs/route.ts
+++ b/app/docs/route.ts
@@ -35,6 +35,8 @@ const VARIANT_C_STYLE = `
   .row a.title { font-weight: 700; }
   .row .tail { color: #888; }
   .row .tail a { color: #888; }
+  .session { display: flex; align-items: baseline; flex-wrap: wrap; gap: 0.75rem; }
+  .session form { margin: 0; }
 </style>`;
 
 // The paste-to-agent prompt and copy button, reused verbatim from the homepage
@@ -203,7 +205,7 @@ export async function GET(req: Request): Promise<Response> {
   const sections: string[] = [];
   sections.push(VARIANT_C_STYLE);
   sections.push(
-    `<div class="body"><pre>Signed in as <code>${esc(email)}</code>. See <a href="/bookmarks">bookmarks</a>.</pre></div>`
+    `<div class="body session"><pre>Signed in as <code>${esc(email)}</code>. See <a href="/bookmarks">bookmarks</a>.</pre><form method="POST" action="/logout"><button type="submit">log out</button></form></div>`
   );
   if (hasAccount) {
     sections.push(ownedSection(owned));
diff --git a/app/logout/route.test.ts b/app/logout/route.test.ts
new file mode 100644
index 0000000..3cbbcdc
--- /dev/null
+++ b/app/logout/route.test.ts
@@ -0,0 +1,50 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { sha256Hex } from "@/lib/auth/tokens";
+
+const mocks = vi.hoisted(() => ({ query: vi.fn() }));
+vi.mock("@/lib/db", () => ({ query: mocks.query }));
+
+import { POST } from "@/app/logout/route";
+
+function request(cookie?: string, origin = "https://justhtml.sh"): Request {
+  const headers = new Headers({ origin });
+  if (cookie) headers.set("cookie", cookie);
+  return new Request("https://justhtml.sh/logout", { method: "POST", headers });
+}
+
+describe("POST /logout", () => {
+  beforeEach(() => {
+    mocks.query.mockReset();
+    mocks.query.mockResolvedValue({ rows: [] });
+  });
+
+  it("revokes the session, clears the cookie, and redirects to login", async () => {
+    const res = await POST(request("other=value; jh_sess=sess_test"));
+
+    expect(res.status).toBe(303);
+    expect(res.headers.get("location")).toBe("/login");
+    expect(res.headers.get("set-cookie")).toBe(
+      "jh_sess=; HttpOnly; Secure; SameSite=Lax; Path=/; Max-Age=0"
+    );
+    expect(mocks.query).toHaveBeenCalledWith(
+      expect.stringContaining("UPDATE sessions SET revoked_at = now()"),
+      [sha256Hex("sess_test")]
+    );
+  });
+
+  it("still clears a stale or missing session cookie", async () => {
+    const res = await POST(request());
+
+    expect(res.status).toBe(303);
+    expect(res.headers.get("set-cookie")).toContain("Max-Age=0");
+    expect(mocks.query).not.toHaveBeenCalled();
+  });
+
+  it("rejects cross-site requests", async () => {
+    const res = await POST(request("jh_sess=sess_test", "https://example.com"));
+
+    expect(res.status).toBe(403);
+    expect(res.headers.has("set-cookie")).toBe(false);
+    expect(mocks.query).not.toHaveBeenCalled();
+  });
+});
diff --git a/app/logout/route.ts b/app/logout/route.ts
new file mode 100644
index 0000000..555abfe
--- /dev/null
+++ b/app/logout/route.ts
@@ -0,0 +1,22 @@
+import { clearSessionCookieHeader, readSessionCookie } from "@/lib/auth/session";
+import { originOk } from "@/lib/auth/request";
+import { sha256Hex } from "@/lib/auth/tokens";
+import { query } from "@/lib/db";
+import { redirect } from "@/lib/page";
+
+export const dynamic = "force-dynamic";
+
+export async function POST(req: Request): Promise<Response> {
+  if (!originOk(req)) return new Response("Forbidden.", { status: 403 });
+
+  const token = readSessionCookie(req);
+  if (token?.startsWith("sess_")) {
+    await query(
+      `UPDATE sessions SET revoked_at = now()
+       WHERE token_hash = $1 AND revoked_at IS NULL`,
+      [sha256Hex(token)]
+    );
+  }
+
+  return redirect("/login", { "Set-Cookie": clearSessionCookieHeader() });
+}
diff --git a/lib/auth/session.ts b/lib/auth/session.ts
index 2c63ed7..d6ac72a 100644
--- a/lib/auth/session.ts
+++ b/lib/auth/session.ts
@@ -103,6 +103,11 @@ export function sessionCookieHeader(token: string): string {
   return `${SESSION_COOKIE}=${token}; HttpOnly; Secure; SameSite=Lax; Path=/; Max-Age=${SESSION_TTL_S}`;
 }
 
+/** Expire the session cookie in the current browser. */
+export function clearSessionCookieHeader(): string {
+  return `${SESSION_COOKIE}=; HttpOnly; Secure; SameSite=Lax; Path=/; Max-Age=0`;
+}
+
 /**
  * Set-Cookie for the login-intent marker — set on the browser that just
  * requested a magic link. Scoped to /login so it rides the emailed