Free chess analysis in your browser

What you get

Every review gives you four things.

• Accuracy for both sides. One number per player, built from how much each move cost. See how it is worked out.
• A label on every move. From brilliant and great down to inaccuracy, mistake and blunder. Moves from known openings are marked as book.
• Key moments with a reason. For the moves that mattered, one plain sentence says why. Each comes with line chips: click one and the line plays out on the board.
• A leak report across games. Enter a Lichess or Chess.com username on the report page and we rank the mistakes that cost you the most over your recent games.

An example from a real review

This is the Opera Game (Paris, 1858), reviewed by the same engine you would use. White finishes at 98.2% accuracy and Black at 82.8%. The card shows move 16, Qb8+, which the engine labelled great.

The note under the board is the fact sentence for that move: “Only this move works here. The runner-up, Qb7, would leave you at about +2.8; your move forces mate in 2.” Every fact comes from engine lines, and every line it quotes is a legal move you can play on the board. Open the full example review.

Why it is free and unlimited

When the engine runs on a company's servers, every review costs that company computing time. Here the engine, Stockfish, is downloaded once and runs in a Web Worker in your browser. The work happens on your device, so a review costs us nothing to ration.

• No account: there is no sign-up step anywhere in the review.
• No game limit: we do not count your reviews.
• Your moves stay on your device: the review sends nothing about your game to our server.

A paid Coach is planned as an extra. The free review is the part described on this page.

How to start

1. Paste a PGN in the box above, or switch to the Lichess or Chess.com tab and enter a username.
2. Press Review. A quick pass runs over every position, then a deeper pass re-checks the moves that look like mistakes or standouts.
3. Open the key moments and play the lines on the board.

Not sure how to get a PGN? The PGN analyzer guide shows where to find it on Chess.com and Lichess.

What it will not do

The engine is a lite build chosen so it runs on ordinary laptops and phones, so it will not match a desktop engine run for hours. Treat labels as a guide to where to look, then check the lines yourself.