diff --git a/README.md b/README.md
index 824f14d..36a3fde 100644
--- a/README.md
+++ b/README.md
@@ -174,6 +174,20 @@ src/
     └── types.ts                      ← shared TypeScript types
 ```
 
+## Browser extension
+
+A small Chrome extension lives in [`extension/`](extension/) that injects a 🪦 "Declared Dead — View Certificate" badge next to the title on any GitHub repo page where the API reports `deathIndex >= 6`.
+
+To load it unpacked:
+
+1. Open `chrome://extensions/`.
+2. Toggle **Developer mode** (top right).
+3. Click **Load unpacked**.
+4. Select the [`extension/`](extension/) directory.
+5. Visit any dead repo, e.g. `https://github.com/atom/atom` — the badge appears next to the repo name and links to its certificate at `commitmentissues.dev/?repo=atom/atom`.
+
+Manifest V3, content-script-only. Cleans up on GitHub's SPA navigation, fails silently when the API is unavailable, and never blocks page render (4-second `AbortSignal.timeout` on the fetch).
+
 ## Testing
 
 ```bash
diff --git a/extension/content.js b/extension/content.js
new file mode 100644
index 0000000..6f6f8af
--- /dev/null
+++ b/extension/content.js
@@ -0,0 +1,162 @@
+// Commitment Issues — tombstone badge for GitHub repo pages.
+//
+// Injects a small "Declared Dead" badge near the repo title when the
+// commitmentissues.dev API reports deathIndex >= 6. Skips silently on any
+// error so it never blocks the page.
+
+(() => {
+  'use strict';
+
+  const API_BASE = 'https://commitmentissues.dev';
+  const SITE_BASE = 'https://commitmentissues.dev';
+  const DEATH_THRESHOLD = 6;
+  const FETCH_TIMEOUT_MS = 4000;
+  const BADGE_ID = 'commitmentissues-tombstone-badge';
+
+  /**
+   * Parse `owner/repo` from `/owner/repo` or `/owner/repo/<rest>`. Returns
+   * null for non-repo paths like `/`, `/owner` (user/org page),
+   * `/orgs/...`, `/settings`, `/explore`, etc.
+   */
+  function parseRepoFromPath(pathname) {
+    const parts = pathname.split('/').filter(Boolean);
+    if (parts.length < 2) return null;
+    // GitHub reserves a small set of top-level paths that are NOT user/org
+    // namespaces. Anything matching one is not a repo URL.
+    const reservedTopLevel = new Set([
+      'orgs', 'settings', 'explore', 'topics', 'trending', 'collections',
+      'events', 'sponsors', 'marketplace', 'pricing', 'enterprise', 'features',
+      'security', 'contact', 'about', 'login', 'logout', 'join', 'signup',
+      'new', 'notifications', 'pulls', 'issues', 'stars', 'codespaces',
+      'gist', 'apps', 'github-copilot', 'copilot', 'organizations',
+    ]);
+    if (reservedTopLevel.has(parts[0].toLowerCase())) return null;
+    // The repo segment can't be a known per-user reserved subpath either.
+    const reservedSecond = new Set(['followers', 'following', 'tabs', 'projects']);
+    if (reservedSecond.has(parts[1].toLowerCase())) return null;
+    return { owner: parts[0], name: parts[1] };
+  }
+
+  function findRepoTitleAnchor() {
+    // GitHub's repo header anchors the repo name with this strong+a structure.
+    // Try a few known-stable selectors before giving up.
+    const candidates = [
+      'strong[itemprop="name"] a',
+      'h1 strong[itemprop="name"] a',
+      'h1 a[data-pjax="#repo-content-pjax-container"]',
+    ];
+    for (const sel of candidates) {
+      const el = document.querySelector(sel);
+      if (el) return el;
+    }
+    return null;
+  }
+
+  function makeBadge(owner, name) {
+    const fullName = `${owner}/${name}`;
+    const a = document.createElement('a');
+    a.id = BADGE_ID;
+    a.href = `${SITE_BASE}/?repo=${encodeURIComponent(fullName)}`;
+    a.target = '_blank';
+    a.rel = 'noopener noreferrer';
+    a.title = 'Declared dead by commitmentissues.dev — view certificate';
+    a.textContent = '🪦 Declared Dead — View Certificate →';
+    Object.assign(a.style, {
+      display: 'inline-flex',
+      alignItems: 'center',
+      gap: '4px',
+      marginLeft: '8px',
+      padding: '2px 8px',
+      borderRadius: '12px',
+      background: '#1e1e1e',
+      color: '#e6e6e6',
+      fontSize: '11px',
+      fontWeight: '500',
+      lineHeight: '18px',
+      textDecoration: 'none',
+      verticalAlign: 'middle',
+      whiteSpace: 'nowrap',
+    });
+    return a;
+  }
+
+  async function fetchDeathIndex(owner, name) {
+    const repoUrl = `https://github.com/${owner}/${name}`;
+    const apiUrl = `${API_BASE}/api/repo?url=${encodeURIComponent(repoUrl)}`;
+    let signal;
+    try {
+      signal = AbortSignal.timeout(FETCH_TIMEOUT_MS);
+    } catch {
+      const ctrl = new AbortController();
+      setTimeout(() => ctrl.abort(), FETCH_TIMEOUT_MS);
+      signal = ctrl.signal;
+    }
+    const res = await fetch(apiUrl, { signal });
+    if (!res.ok) return null;
+    const body = await res.json();
+    const idx = typeof body?.deathIndex === 'number' ? body.deathIndex : null;
+    return idx;
+  }
+
+  let lastInjectedFor = null;
+
+  async function tryInject() {
+    const existing = document.getElementById(BADGE_ID);
+    if (existing) existing.remove();
+
+    const repo = parseRepoFromPath(location.pathname);
+    if (!repo) {
+      lastInjectedFor = null;
+      return;
+    }
+
+    const fullName = `${repo.owner}/${repo.name}`;
+    if (lastInjectedFor === fullName) return;
+
+    const anchor = findRepoTitleAnchor();
+    if (!anchor) return;
+
+    let deathIndex = null;
+    try {
+      deathIndex = await fetchDeathIndex(repo.owner, repo.name);
+    } catch {
+      return;
+    }
+    if (deathIndex === null || deathIndex < DEATH_THRESHOLD) {
+      lastInjectedFor = fullName;
+      return;
+    }
+
+    const stillSamePage = parseRepoFromPath(location.pathname);
+    if (!stillSamePage || `${stillSamePage.owner}/${stillSamePage.name}` !== fullName) {
+      return;
+    }
+
+    const titleStrong = anchor.parentElement;
+    const insertAfter = titleStrong?.parentElement === document.querySelector('h1')
+      ? titleStrong
+      : anchor;
+    insertAfter.parentNode.insertBefore(makeBadge(repo.owner, repo.name), insertAfter.nextSibling);
+    lastInjectedFor = fullName;
+  }
+
+  let lastUrl = location.href;
+  function observeNavigation() {
+    const fire = () => {
+      if (location.href === lastUrl) return;
+      lastUrl = location.href;
+      tryInject();
+    };
+    window.addEventListener('popstate', fire);
+    document.addEventListener('pjax:end', fire);
+    document.addEventListener('turbo:load', fire);
+    document.addEventListener('turbo:render', fire);
+    const mo = new MutationObserver(() => {
+      if (location.href !== lastUrl) fire();
+    });
+    mo.observe(document.body, { childList: true, subtree: true });
+  }
+
+  tryInject();
+  observeNavigation();
+})();
diff --git a/extension/icon.png b/extension/icon.png
new file mode 100644
index 0000000..bd91211
Binary files /dev/null and b/extension/icon.png differ
diff --git a/extension/manifest.json b/extension/manifest.json
new file mode 100644
index 0000000..7750ddb
--- /dev/null
+++ b/extension/manifest.json
@@ -0,0 +1,21 @@
+{
+  "manifest_version": 3,
+  "name": "Commitment Issues Tombstone Badge",
+  "version": "0.1.0",
+  "description": "Shows a tombstone badge on GitHub repo pages when commitmentissues.dev has marked them dead.",
+  "icons": {
+    "32": "icon.png",
+    "128": "icon.png"
+  },
+  "permissions": [],
+  "host_permissions": [
+    "https://commitmentissues.dev/*"
+  ],
+  "content_scripts": [
+    {
+      "matches": ["https://github.com/*"],
+      "js": ["content.js"],
+      "run_at": "document_idle"
+    }
+  ]
+}