How to analyse a game
- Load the game. Copy the PGN from the game's share or export menu on the site you played on, paste it in the box, and tap Load game. A FEN works too, to start from a position. Or try the sample game.
- Tap Analyse the game. Stockfish 19 checks every position to depth 14 (at most 1.5 seconds each) on your device, then looks again, deeper, at every move that seems to lose ground.
- Read the graph and the marks. The graph shows White's chances move by move; a drop is where something went wrong. Moves are marked ?! (inaccuracy), ? (mistake) or ?? (blunder), with the better move named.
- Explore. Step with the arrow buttons or your keyboard's ← and → keys. Play a different move on the board to try a side line, and tap Best move in this position for the top three moves.
How moves are marked
First, every position is scored at depth 14. Any move that seems to lose ground is then searched again from the position before it, to depth 18: once for Stockfish's best move and once for the move that was played. We compare the mover's winning chances after the two (the same win-chance curve as the eval bar). If the move played was not the engine's choice and it cost:
| Drop in winning chances | Mark |
|---|---|
| 5 to 9.9 percentage points | ?! Inaccuracy |
| 10 to 14.9 points | ? Mistake |
| 15 points or more | ?? Blunder |
So a move that throws away a one-pawn edge in an equal game counts for more than the same pawn in a position that was already lost. The re-check exists because a quick search can miss a deep tactic and blame a good move; the deeper search at the same position fixes most of those. For a critical moment, also use Best move in this position.
The sample game
The sample is the Opera Game, played by Paul Morphy against the Duke of Brunswick and Count Isouard in a box at the Paris Opera in 1858. It is one of the most-taught games in chess: White develops quickly, opens lines with sacrifices, and mates on move 17 with Rd8#.
Fair play
Analyse games after they are finished. Using engine help during a game you are playing breaks the rules of every chess site and over-the-board event.