Run Stockfish online, in your browser
The strongest open-source chess engine in the world, running locally in your browser tab on any position you give it.
Evaluate a sample position → The Fried Liver position, where the natural recapture is the losing move.
What Stockfish is
Stockfish is a free, open-source chess engine and, for most of the last decade, the strongest chess-playing entity on earth. It combines a very fast search with an NNUE neural network evaluation - a small network trained to judge positions, evaluated efficiently enough to run millions of times per second on ordinary hardware.
In practice that means it plays several hundred rating points above the world champion, and its evaluation of a quiet position is as close to objective truth as chess currently gets.
Why running it in the browser is better
- No queue. Server-side analysis shares one machine among everyone using the site. Here the engine runs on your device, so its whole speed is yours.
- No install. Nothing to download, and it works on a locked-down work laptop or a phone.
- Multi-threaded. On browsers that support it, the engine uses several CPU cores at once for substantially greater depth.
- Private. The positions you analyse are evaluated locally rather than sent somewhere to be processed.
Reading the evaluation
The number is measured in pawns, from White's point of view: +1.2 means White is about a pawn better, -3.0 means Black is winning a piece's worth. A # value like #4 means forced mate in four.
Two cautions worth keeping. First, the evaluation assumes best play from both sides - a position rated +0.8 may be much easier to play for the defender in practice. Second, evaluation at low depth in a sharp position can swing wildly; let it settle before drawing conclusions.
The engine tells you what, not why. When it says a move is bad, put the move on the board and look at the line it gives - understanding the refutation is the part that makes you stronger.
Keep going
Analysis board
The full board: arrows, opening explorer and position tools.
Game analyzer
Run the engine across a whole game and get every mistake marked.
Play a bot
Face an opponent that plays like a human, not like an engine.
Frequently asked questions
Is Stockfish free?
Yes. Stockfish is open-source software released under the GNU GPL, free to use and to modify. Running it here costs nothing and needs no account.
Do I need to download anything?
No. The engine is compiled to WebAssembly and loads in the browser tab. Once loaded it will keep working even without a connection.
How strong is Stockfish?
Far stronger than any human player - several hundred Elo above the world champion on standard hardware. For any practical analysis question at club level, its assessment can be treated as correct.
What does the evaluation number mean?
It is measured in pawns from White's perspective. +1.0 means White is a pawn better with best play; a value like #3 means mate in three. It always assumes both sides play the best moves available.