Import a game or set up any position, and Stockfish analyzes every move in your browser: the evaluation, the best moves as arrows on the board, and a report of every mistake. Free, with nothing to install and no account.
Analyze a gameStockfish scores every position as you move the pieces or step through a game, with its best lines beside the board.
Swings towards whichever side is better, so you see the balance at a glance without reading a number.
The engine's top choices drawn on the board and colored by how good each one is, instead of a list of notation.
An accuracy score for each player, brilliant moves marked in teal, and every inaccuracy, mistake and blunder for both sides.
Every candidate move and its evaluation at once, for the whole tactical picture rather than one best line.
Pick a piece and the engine scores it on every square, so you can see where a misplaced piece wants to go.
Quiz yourself against the engine's choice and find out straight away whether you would have found it.
Build any position by hand, with who is to move, castling rights and en passant, then analyze it.
Press Import Game and paste a game's link from Chess.com or Lichess, its PGN, or a FEN for a single position. The game opens on the board with the engine running: step through it with the arrow keys, and the report marks the moves that decided it. To see it on something you know, open Morphy's Opera Game (Paris, 1858).
The game report compares every move with the engine's choice and grades it as a best move, a good one, an inaccuracy, a mistake or a blunder - for both players, so you see the chances your opponent gave you as well as the ones you gave away. Each player gets an accuracy score out of 100, and sound sacrifices are marked as brilliant moves. Click any marked move to go to that position, with the engine running, and find out why.
What to look for in your own games:
Stockfish runs locally, in the browser tab, using WebAssembly. Your moves are not queued behind other people's analysis on a shared server, there is nothing to install, and there is no cap on how many games you review. Even the free single-threaded engine searches far deeper than any club game needs, and a subscription unlocks multi-threaded builds that use several CPU cores at once.
That also means it works the same on a phone, and on a work laptop where you cannot install software.
Press Import Game, paste the game's link from Chess.com or Lichess or its PGN, and run the game report. Stockfish analyzes it in your browser and marks every inaccuracy, mistake and blunder for both sides, free and without an account.
Yes. The board, the engine, the game report and the puzzles are free to use with no account. There is a paid tier with faster, multi-threaded engines, but nothing on this page needs it.
No. Open the board and start analyzing. An account is only useful if you want your games saved across devices.
Stockfish, the strongest open-source chess engine, compiled to WebAssembly and running inside your browser rather than on a server.
Yes. Press Import Game and paste the game's link from Chess.com or Lichess, or its PGN. The game opens on the board with the engine running, and the report grades every move.
Yes. Paste a FEN into Import Game, or set the position up on the board editor, and the engine evaluates it straight away.
Yes. The eval bar sits beside the board and moves with the position, alongside the score and the engine's best lines. It works in the board editor too, so you can see how a position is judged while you set it up.
Yes. Each player gets an accuracy score from 0 to 100, and every sound sacrifice is marked brilliant alongside the best moves, inaccuracies, mistakes and blunders - for as many games as you like.
A move that drops a large amount of evaluation compared with the best available move - typically enough to change the result of the game with correct play. Inaccuracies and mistakes are the same idea with smaller thresholds.