Guides / How a chess game review works
How a chess game review works
A full review of a 40-move game means judging about 80 positions. Searching every one of them to the same great depth would take minutes, and most positions do not need it. GChess Review does it in two passes instead.
1. The quick pass
The engine, Stockfish 19, looks at every position once, at a lower depth than the one you chose, so the whole game has a first verdict within seconds. It records its best line and the second-best line for each position. From the change in score between one move and the next, it finds where the game swung.
2. The deep pass
The positions that mattered most, the critical moments, are searched again at the full depth of the strength you chose: about a fifth of the game's moves, at least 4 and at most 24. These are the moves where a mistake cost the most, and the positions where only one move held. That second look is what allows the review to grade a move Great: the label needs both the best and the second-best move searched at full depth, so the gap between them can be trusted.
3. Grading every move
Each move is then labelled from how much it cost, measured in expected points. The exact rules are on the move classifications page.
The three strengths
- Quick: depth 16 for the critical moments, two lines per position. The default, and fast on a phone.
- Standard: depth 22, two lines.
- Deep: depth 28, three lines, using the most memory and processor time.
Deeper means slower and, now and then, a different verdict on a sharp move. Quick is right for most games; switch to Deep for a game you want to study properly.
Why it runs on your computer
The engine is compiled to WebAssembly and runs in your browser, so a review does not wait in a server queue and your games are never uploaded. The standard engine, Stockfish 19 Lite, is about 1.6 MB and loads straight away. The Full engine is about 99 MB, stronger, and downloaded only if you choose to; it is then kept in your browser's cache. Where the browser allows it, the engine uses several threads at once. More on that in Stockfish in your browser.
The review opens where the game turned
Instead of starting at move one, the review opens at the moment the result was decided. You can step through from there, see the engine's line drawn on the board, and play your own moves from any position to see what would have happened.