diff --git a/public/index.html b/public/index.html
index 80a76f3..0c791ff 100644
--- a/public/index.html
+++ b/public/index.html
@@ -59,6 +59,13 @@ <h2 style="margin: 0 0 0.4rem">This page is talking to its own backend</h2>
           Everything below is served by the same instance, through <code>/sdk.js</code>. Open a second tab —
           new entries appear in both without a refresh (that's the realtime layer).
         </p>
+        <p id="mt-notice" class="muted small" style="display: none; margin: 0 0 0.8rem; max-width: 64ch; padding: 0.6rem 0.85rem; border: 1px solid var(--border); border-radius: 10px"></p>
+        <!-- Shown only on a multi-tenant server: paste a project key (kept in this tab only). -->
+        <form id="key-form" style="display: none; gap: 0.5rem; margin: 0 0 1.3rem; max-width: 64ch; align-items: center">
+          <input id="key-input" type="password" autocomplete="off" placeholder="Project key (pk_…)" style="flex: 1" />
+          <button type="submit">Use key</button>
+          <button type="button" id="key-clear" class="muted" style="display: none">Clear</button>
+        </form>
         <div class="grid" style="grid-template-columns: repeat(auto-fit, minmax(300px, 1fr))">
           <section class="card">
             <h3 style="margin: 0 0 0.8rem">💬 Guestbook <span class="muted small">data + live sync</span></h3>
@@ -108,7 +115,21 @@ <h2 style="margin: 0 0 1.3rem">Everything a generated app needs</h2>
 
     <script src="/sdk.js"></script>
     <script>
-      const api = Zero(); // same-origin
+      // In multi-tenant mode every data/file call needs a project key. The public
+      // demo has none, so let the operator paste one. It's kept in sessionStorage
+      // (this tab only, gone when it closes) — never in the URL.
+      const KEY_STORE = 'zero_demo_key';
+      let demoKey = sessionStorage.getItem(KEY_STORE) || null;
+      let api = demoKey ? Zero('', { apiKey: demoKey }) : Zero(); // same-origin
+      let room = null;
+      const notice = (html) => {
+        const el = document.getElementById('mt-notice');
+        if (!html) return void (el.style.display = 'none');
+        el.innerHTML = html;
+        el.style.display = '';
+      };
+      const needsKey = (e) => e && e.status === 401;
+      const keyHint = 'Paste a project key above to use the demo.';
       const escapeHtml = (s) =>
         String(s).replace(/[&<>"']/g, (c) => ({ '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' }[c]));
 
@@ -119,6 +140,17 @@ <h2 style="margin: 0 0 1.3rem">Everything a generated app needs</h2>
           const provider = info.endpoints && info.endpoints.ai && info.endpoints.ai.provider;
           document.getElementById('status').innerHTML =
             `<span class="dot live"></span> live${info.version ? ' · v' + escapeHtml(info.version) : ''}${provider ? ' · ai:' + escapeHtml(provider) : ''}`;
+          // Multi-tenant: reveal the key box; explain it if no key is set yet.
+          if (info.mode === 'multi-tenant') {
+            document.getElementById('key-form').style.display = 'flex';
+            updateKeyStatus();
+            if (!demoKey) {
+              notice(
+                'This server runs in <b>multi-tenant</b> mode, so the live demo needs a project key. ' +
+                  'Create one in the <a href="/admin">dashboard</a> and paste it above.',
+              );
+            }
+          }
         } catch {
           document.getElementById('status').textContent = 'offline';
         }
@@ -135,55 +167,113 @@ <h2 style="margin: 0 0 1.3rem">Everything a generated app needs</h2>
       });
 
       async function loadEntries() {
-        const docs = await api.data('guestbook').list({ sort: '-createdAt', limit: 25 });
         const el = document.getElementById('entries');
-        el.innerHTML = docs.length
-          ? docs
-              .map(
-                (d) =>
-                  `<li><span>${escapeHtml(d.message)}</span> <span class="muted small">${new Date(d.createdAt).toLocaleTimeString()}</span></li>`,
-              )
-              .join('')
-          : '<li class="muted">No messages yet — be the first.</li>';
+        try {
+          const docs = await api.data('guestbook').list({ sort: '-createdAt', limit: 25 });
+          el.innerHTML = docs.length
+            ? docs
+                .map(
+                  (d) =>
+                    `<li><span>${escapeHtml(d.message)}</span> <span class="muted small">${new Date(d.createdAt).toLocaleTimeString()}</span></li>`,
+                )
+                .join('')
+            : '<li class="muted">No messages yet — be the first.</li>';
+        } catch (e) {
+          el.innerHTML = `<li class="muted">${needsKey(e) ? keyHint : 'Could not load entries.'}</li>`;
+        }
       }
 
       async function loadFiles() {
-        const files = await api.files.list();
         const el = document.getElementById('files');
-        el.innerHTML = files.length
-          ? files
-              .map(
-                (f) =>
-                  `<li><a href="${api.files.url(f.id)}" target="_blank" rel="noopener">${escapeHtml(f.name)}</a> <span class="muted small">${f.size} bytes</span></li>`,
-              )
-              .join('')
-          : '<li class="muted">No files yet.</li>';
+        try {
+          const files = await api.files.list();
+          el.innerHTML = files.length
+            ? files
+                .map(
+                  (f) =>
+                    `<li><a href="${api.files.url(f.id)}" target="_blank" rel="noopener">${escapeHtml(f.name)}</a> <span class="muted small">${f.size} bytes</span></li>`,
+                )
+                .join('')
+            : '<li class="muted">No files yet.</li>';
+        } catch (e) {
+          el.innerHTML = `<li class="muted">${needsKey(e) ? keyHint : 'Could not load files.'}</li>`;
+        }
       }
 
       document.getElementById('post-form').addEventListener('submit', async (e) => {
         e.preventDefault();
         const input = document.getElementById('msg');
         if (!input.value.trim()) return;
-        await api.data('guestbook').create({ message: input.value });
+        try {
+          await api.data('guestbook').create({ message: input.value });
+          input.value = '';
+        } catch (e) {
+          notice(needsKey(e) ? 'Saving needs a project key — paste one above.' : 'Could not save: ' + e.message);
+        }
+      });
+
+      // (Re)connect the SDK with the current key: refresh both lists and the live
+      // guestbook subscription. Called on load and whenever the key changes.
+      function connect() {
+        api = demoKey ? Zero('', { apiKey: demoKey }) : Zero();
+        if (room) {
+          try {
+            room.close();
+          } catch {}
+        }
+        room = api.data('guestbook').subscribe((change) => {
+          if (change.type === 'created' || change.type === 'deleted') loadEntries();
+        });
+        loadEntries();
+        loadFiles();
+      }
+
+      function updateKeyStatus() {
+        const clear = document.getElementById('key-clear');
+        const input = document.getElementById('key-input');
+        if (demoKey) {
+          input.placeholder = 'Using a project key';
+          clear.style.display = '';
+        } else {
+          input.placeholder = 'Project key (pk_…)';
+          clear.style.display = 'none';
+        }
+      }
+
+      document.getElementById('key-form').addEventListener('submit', (e) => {
+        e.preventDefault();
+        const input = document.getElementById('key-input');
+        const v = input.value.trim();
+        if (!v) return;
+        demoKey = v;
+        sessionStorage.setItem(KEY_STORE, v);
         input.value = '';
+        notice('');
+        updateKeyStatus();
+        connect();
       });
 
-      // Live: new entries from any browser tab show up here without a refresh.
-      api.data('guestbook').subscribe((change) => {
-        if (change.type === 'created' || change.type === 'deleted') loadEntries();
+      document.getElementById('key-clear').addEventListener('click', () => {
+        demoKey = null;
+        sessionStorage.removeItem(KEY_STORE);
+        updateKeyStatus();
+        connect();
       });
 
       document.getElementById('file-form').addEventListener('submit', async (e) => {
         e.preventDefault();
         const input = document.getElementById('file');
         if (!input.files[0]) return;
-        await api.files.upload(input.files[0]);
-        input.value = '';
-        loadFiles();
+        try {
+          await api.files.upload(input.files[0]);
+          input.value = '';
+          loadFiles();
+        } catch (e) {
+          notice(needsKey(e) ? 'Uploading needs a project key — paste one above.' : 'Upload failed: ' + e.message);
+        }
       });
 
-      loadEntries();
-      loadFiles();
+      connect();
     </script>
   </body>
 </html>
diff --git a/test/api.test.ts b/test/api.test.ts
index cd31f8e..d6812e1 100644
--- a/test/api.test.ts
+++ b/test/api.test.ts
@@ -85,6 +85,18 @@ test('serves the SDK and llms.txt', async () => {
   assert.equal(llms.status, 200);
 });
 
+test('serves the homepage demo, which is multi-tenant aware (accepts a ?key=)', async () => {
+  const res = await fetch(`${base}/`);
+  assert.equal(res.status, 200);
+  assert.match(res.headers.get('content-type') ?? '', /text\/html/);
+  const html = await res.text();
+  // The demo lets you paste a project key (kept in sessionStorage) so it works on
+  // a multi-tenant server, and shows a notice explaining how.
+  assert.match(html, /key-form/);
+  assert.match(html, /sessionStorage/);
+  assert.match(html, /mt-notice/);
+});
+
 test('serves the examples gallery and apps', async () => {
   for (const p of ['/examples.html', '/examples/todo.html', '/examples/chat.html', '/examples/notes.html']) {
     const res = await fetch(`${base}${p}`);