♟ Chess Review

Free, open-source game review for your online chess games, powered by Stockfish NNUE running locally in your browser. One click turns any Chess.com or Lichess game into a full review — accuracy scores, move-by-move classifications, an evaluation graph, and an estimated rating. Local analysis needs no account or server, and no manual PGN copying.

Learn with Chess Review opens from the button beneath Engine, beside the move controls. By default, the review panels morph into one learning workspace while the board and top bar stay in place. Settings → General → Learning experience offers Morph in place, Morph in place 2, Morph in place 3, Studio Morph, Minimal morph, Board morph, and the original Separate page layout. Each morph has its own design and timing. The transition also runs when returning to review and respects reduced-motion preferences. Morph in place 2 glides the intact board into a centered study layout and keeps Settings available alongside learning, with reserved space on desktop windows. Morph in place 3 keeps the review board size and familiar piece handling while the surrounding panels transition into learning. The learning workspace includes 23 concept lessons with 47 exercises, 25,000 offline puzzles, 1/5/10-minute challenges, and 12 opening courses with 24 annotated lines. Lessons use move, square-selection and position-reading exercises. Opening practice supports both colors and automatic opponent replies. Progress and bookmarks stay in your browser, and Back to review restores your game position and orientation. The learning objective and progress tracker preserves the full development brief for work on another computer; content sources record licensing and validation scope.

The right-hand Settings panel includes an optional Concepts tab after General and Engine. A separate Concepts panel to the right of Accuracy and Engine uses those same findings, ordered by likely relevance and phrased from your playing side. It follows the selected move, includes every match, and separates insights with space. Its top aligns with the coach commentary panel; its bottom aligns with Engine. Expand an insight's evidence to inspect the original explanation and exact scope. Accuracy and the existing move commentary retain their scoring and behavior.

The Settings Concepts panel remains the raw inspection and game-debug view. Check Enable concept analysis to list supported findings for the selected move, with exact verified scopes and game-wide debug metrics. It defaults off and stops its worker immediately when disabled. Findings use completed E080 research's bounded mechanics; broader strategic benefits and coaching usefulness remain unproven. Existing scores and coach comments are unchanged.

Source: https://github.com/T-Julsgaard/Chess-Review

Chrome webshop: https://chromewebstore.google.com/detail/chess-review/pdbffcjdmcadihmnmenkadndbdbigfam

Firefox Add-ons: https://addons.mozilla.org/en-US/firefox/addon/chess-review/

Watch the introduction

Click the image below to watch the introduction video.

Features

• One-click review of any Chess.com or Lichess game — or paste a game URL / raw PGN.
• Accuracy estimates for both players, calculated from local Stockfish analysis using the extension's scoring rules. Scores can differ from other review tools.
• Move classifications from Brilliant to Blunder, with an evaluation graph and best-move arrows.
• Estimated rating — a rough guide to the level each player performed at in the game.
• Opening detection from an offline book, named even for PGNs without headers.
• Rated alternatives while reviewing a game, using the same classification rules as the played moves. Exploring does not change the original game or its accuracy.
• Stockfish 18 NNUE is the default, with Stockfish 19 Lite as a compact alternative. Both are bundled locally and available in Settings.
• Recoverable analysis errors with a Retry button; unfinished reviews are not saved as completed games.
• Analysis runs on your machine — game lookup requests go directly to the chess platforms; no developer backend or analytics.

Usage

1. Open a finished game on Chess.com or Lichess.
2. Click the extension icon → Analyze this game, or press Ctrl+Shift+Y.
3. Stockfish reviews the game in an analysis tab.

You can also paste a game URL or PGN into the popup. If your username cannot be detected, enter it once; it is remembered locally. Chess Review is intended for review after play.

Settings let you choose an engine, rating mode, board, pieces, sounds, coach and category-badge appearance. Badge numbers describe move categories; they are separate from position evaluation and game accuracy.

Both engines offer Use recorded rating and Moves only. The first compares your performance with public players near the rating saved in the game; the second ignores that rating and estimates a blitz rating level from your choices. Without a saved rating, the review falls back to Moves only, which needs at least ten nonforced decisions. Each engine uses its own models.

Optional Dopamine mode

Choose Settings → General → Interface presets → Review experience → Dopamine for a more expressive review: purple board and interface, move-colored accents, and reactions centered on the move's destination. Brilliant moves send teal waves across the squares; blunders produce a red shockwave and shards. Other categories have smaller reactions. Effects never cover the board with a text box or intercept input. The same settings section offers Preview Brilliant effect and Preview Blunder effect buttons, without changing your move's actual classification.

The commentary explains available engine evidence: immediate mate, a mating evaluation, a legal capture, material changes in the shown line, or the evaluation loss when no specific tactic is established. You can explore the reply and the engine's better alternative. Explanations use existing local analysis; a shown continuation is not a promise that every future move is forced. Missing or invalid lines never produce invented tactical claims.

Normal remains the default. The mode and original visual preferences are saved separately; switching back restores the original appearance and commentary. The default Modern layout gives the explanation panel more room only in Dopamine mode; custom arrangements stay intact. Reduced motion or disabling Animation keeps a static destination outline. No extra engine searches, network services, extension permissions, dependencies, or changes to classifications and accuracy are needed.

For just the explanation text with your usual appearance, turn on Settings → General → Coach → Engine explanations. It works with any coach, including No coach, and saves your choice independently of the review mode. Engine explanations and Special replies are alternative reply styles: turning either on switches the other off. Dopamine keeps engine explanations by default until you explicitly choose a reply style in Coach settings.

Scoring and reproducibility

Chess Review is open source and uses local Stockfish analysis with documented scoring models. The repository includes the fitting tools, public-data evidence and reference results needed to inspect and reproduce the bundled numerical models.

With Node.js 24 or later, reproduce the bundled coefficients and reference scores offline:

node tools/calibration/reproduce-public.mjs

This check replays the included evidence without rerunning engine searches. The methodology documents the inputs, calculations and limitations. Estimated ratings are approximate.

Move categories follow documented classification rules. See the special annotations guide for their definitions and sources, and the repository guide for the supporting files.

Research and future methods

The separate research workspace investigates improvements to accuracy, estimated ratings and move categories against our own documented baseline. It records reproducible experiments, successful and unsuccessful findings, evidence limits and implementation decisions. Research candidates become part of the extension only through a documented promotion. See the research index for current state and next questions.

Install

Install from the Chrome Web Store or Firefox Add-ons using the links above. For a local Chrome installation:

1. Download or clone this repository.
2. Open chrome://extensions and enable Developer mode (top-right).
3. Click Load unpacked and select the project folder.

Privacy

Games are fetched from Chess.com's and Lichess's public APIs and analyzed locally with bundled WebAssembly builds of Stockfish. Lookup requests include public player usernames or game IDs. No games or analysis are sent to the developer or analytics services. Firefox discloses the browsing activity and website content used for these requests. Sharing a game copies an encoded, unencrypted PGN/metadata link to your clipboard; anyone you send it to can read that information. See PRIVACY.md.

Optional puzzle leaderboards have a Cloudflare Workers + D1 service, server-verified ranked play and matching screens for all three modes. They are disabled until a deployment is configured. See leaderboard setup and security. Participation requires explicit opt-in before viewing or uploading. Nationality is optional; Settings → General → Leaderboard provides sharing, opt-out and online deletion controls. Ordinary offline progress stays local.

Maintained-source checks

The Maintained source workflow runs npm run verify:source and npm run verify:history before the test suites. The history check inspects reachable commits and historical text blobs in batches targeting 16 MiB, so growing research history does not overflow one combined subprocess output buffer. All existing content and path checks remain active.

The complete research suite runs in a separate Windows CI job with the original Python runtime bound by the E211 saved observations. Setup verifies the pinned archive, retained executable hash, and full build version; existing research evidence and checks remain unchanged. See runtime setup.

Release packages

Run npm ci, npm test, npm run verify:engines, and npm run build. The build creates separate Chrome and Firefox ZIPs under web-ext-artifacts/, with browser-specific manifests and no development dependencies or tests. Each build has its own release directory, source snapshot, and SHA-256 package checksums. See RELEASE.md for store reviewer notes and validation commands.

License & attributions

Chess Review's own code is licensed under the GNU General Public License v3.0 (see LICENSE), matching the bundled Stockfish engine. Bundled third-party assets (engine, pieces, sounds, opening book, libraries) keep their own licenses — see ATTRIBUTIONS.md and THIRD_PARTY_NOTICES.md. Some asset redistribution rights remain unresolved as documented in the attributions; the project's GPL license does not grant rights to those assets. Corresponding source for the GPL/AGPL components is available from the upstream projects listed there.

Disclaimer: Chess Review is an independent, unofficial tool. It is not affiliated with, endorsed by, or sponsored by Chess.com or Lichess. Those names are used only to describe the sites it reads games from (nominative reference); all trademarks belong to their respective owners.