A Chrome extension (Manifest V3) that summarizes YouTube videos from their full transcript using Google's Gemini API — so you can read the summary instead of watching.

• 📝 Summarize button on every video — home feed tiles, watch-page related videos, and the watch page itself. One click summarizes that video.
• Everything in the side panel. Summaries render in Chrome's side panel, so you can keep the video on screen while you read. (There's also a Summarize current video button inside the panel.)
• Transcript-first, with a fallback. Summaries are built from the real transcript. When captions are unavailable (YouTube pot-token gating, or no captions at all), it falls back to Gemini's native video understanding, so a normal public video never just fails.
• Streaming output. The summary streams in token-by-token instead of waiting for the full response.
• Safe by default. Your API key lives in the background service worker and never reaches the page. Rendered text is HTML-escaped; links are protocol-sanitized. Dark mode included.

Model: gemini-2.5-flash (v1beta streamGenerateContent). The transcript path is cheap and fast; the video-understanding fallback is the reliability backstop. Private/members-only videos with no captions are the one case neither path can reach — the extension says so clearly instead of guessing.

Requires Chrome 114+ (side panel API) and Node 18+.

1. Build the extension:

   npm install
   npm run build && npm run icons

   This produces the bundled content.js, background.js, popup.js, and the icon PNGs.

2. Load it into Chrome:

   • Open chrome://extensions/
   • Enable Developer mode (top right)
   • Click Load unpacked and select this folder

3. Add your Gemini key:

   • Click the extension icon to open the side panel
   • Open ⚙️ Settings, paste your Gemini API key (get one free at Google AI Studio), and Save

• Any video tile (home feed or related videos): click 📝 Summarize → the summary opens in the side panel.
• Watch page: click 📝 Summarize under the title, or open the side panel and click Summarize current video.

npm run build         # bundle src/ → content.js / background.js / popup.js (esbuild)
npm run build:watch   # rebuild on change
npm test              # unit + integration tests (vitest + jsdom)
npm run test:coverage # coverage report
npm run e2e           # Playwright: load the extension into Chromium, drive real YouTube
npm run icons         # regenerate icon PNGs

Source lives in src/ and is bundled to the extension root. Shared, unit-tested logic is in src/lib/:

Logged-out YouTube has an empty home feed, so the E2E run can optionally use your real cookies:

node tests/e2e/import-brave-cookies.mjs   # exports Brave's youtube.com cookies (one Keychain prompt)
npm run e2e                               # now runs logged in

Cookies are written to .context/youtube-cookies.json (gitignored). It holds live session credentials — delete it when you're done (rm .context/youtube-cookies.json). The core injection e2e tests use the search-results page and pass without it; only the "logged-in home feed" test needs a session (it skips when absent).

Don't want to use a paid Gemini key? .claude/commands/yt-summarize.md is a Claude Code slash command that fetches a video's transcript with the free youtube-transcript-api and has Claude itself summarize it — no API key.

/yt-summarize https://www.youtube.com/watch?v=VIDEO_ID

To use it anywhere, copy it to your global commands dir:

cp .claude/commands/yt-summarize.md ~/.claude/commands/

scripts/yt-transcript.py is the standalone extractor it uses (kept in an isolated venv, so it works on PEP-668 "externally managed" Python).

• Architecture — component diagram, summarization ladder, message protocol
• Security model — XSS prevention, URL sanitization, API key isolation

MIT.