Rookahead

A chess analysis board running Stockfish 19 in the browser, multi-threaded, with the full NNUE network.

• Live analysis of any position: up to 5 engine lines, best-move arrows, eval bar
• Game review: every move graded with Rookahead's verdicts (Legendary, Clutch, Best, Strong, Solid, Theory, Slip, Mistake, Oversight, Blunder, Forced), accuracy per player, an eval graph marking the key moments, and a step-through mode with commentary
• Paste a PGN / FEN, or import recent games by username
• Play your own moves on the board to explore side variations (promote or delete them later)
• Clocks from the PGN, keyboard navigation, board themes, and the session survives a refresh
• Move sounds (synthesised in the browser, no audio files) and animated pieces, verdicts and summary

Running it

npm install     # also copies the Stockfish builds into public/engine/
npm run dev     # http://localhost:5173

Requires Node 20+. It starts on the Lite engine, a 2 MB network that loads instantly (still far stronger than any human). Pick Full in Settings for the strongest analysis: that downloads the ~100 MB network once, and the browser caches it after that.

Multi-threading

Multi-threaded WASM needs SharedArrayBuffer, which browsers only allow on cross-origin isolated pages. The dev and preview servers send the required headers (see vite.config.ts):

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

If you host the built dist/ elsewhere, send those two headers too, or the app falls back to a single thread.

How moves are classified

Rookahead's own rules for every verdict live in docs/rulebook.md; src/lib/classify.ts follows them. The opening book is Lichess's CC0 opening list (src/data/openings.json).

• Accuracy — Lichess's open formula (volatility-weighted and harmonic means of per-move accuracy)

To rebuild the opening book: node scripts/build-openings.mjs <dir with a.tsv … e.tsv> from https://github.com/lichess-org/chess-openings.

Keyboard

Key	Action
← / →	Previous / next move
↑ / Home	Start of the game
↓ / End	End of the current line
F	Flip the board
L	Toggle the engine
Space	Play through the moves

Scripts

Command
npm run dev	Dev server
npm run build	Type-check and build to dist/
npm run preview	Serve the build (with isolation headers)
npm test	Unit tests (Vitest)
npm run lint	Lint (oxlint)

Set localStorage.setItem('rookahead.debug', '1') in the browser console to log all UCI traffic.

Layout

src/
  engine/Engine.ts        Stockfish worker wrapper: UCI, one-search-at-a-time queue, cancellation
  hooks/useAnalysis.ts    Live analysis (with per-position cache) and full-game review
  hooks/useEngine.ts      Engine lifecycle
  lib/tree.ts             Game tree (main line + variations), PGN import/export
  lib/uci.ts              UCI "info" line parser
  lib/evaluation.ts       Score conversion, win %, formatting
  lib/chesscom.ts         Chess.com public API client
  components/             Board (Chessground), eval bar & graph, move list, engine lines, dialogs

Licences

Rookahead is free software under the GNU General Public License v3.0 or later (see LICENSE).

It builds on Stockfish.js (GPL-3.0) and Chessground (GPL-3.0-or-later), so anyone serving the app must also offer its source under the GPL. The opening book comes from Lichess's chess-openings (CC0) and the Geist fonts are under the SIL Open Font License.