Run Stockfish 19 online, in your browser
Stockfish 19 is the latest release of the strongest open-source chess engine. Here it runs in your browser tab, on any position you give it.
Evaluate a sample position → The Fried Liver position, where the natural recapture is a risky move that lets White sacrifice a knight on f7.
What Stockfish is
Stockfish is a free, open-source chess engine, and for most of the last decade it has been the strongest chess player on earth, human or machine. It pairs a very fast search with an NNUE evaluation: a small neural network trained to judge positions, cheap enough to run millions of times a second on an ordinary computer.
It is so far ahead of the best humans that the gap can't be measured in Elo, because no human scores enough wins or draws against it. On a quiet position, its evaluation is as close to the truth as chess analysis currently gets.
Why running it in the browser is better
- No queue. A site that analyzes on its own servers shares those machines among all its users. Here the engine runs on your device, so all of its speed is yours.
- No install. The engine loads with the page, so there is nothing to set up, and it works on a locked-down work laptop or a phone.
- Multi-threaded, with a subscription. The free engine runs on one CPU core. Subscribers get multi-threaded builds that use several cores at once, so the engine searches deeper in the same time.
Stockfish 19 and the older versions
Stockfish 19 is the current release, and it is in the engine menu on the analysis board. The board starts on a small, fast-loading engine so a first visit never waits on a large download; switching to Stockfish 19 takes one click, and the choice is remembered.
The older versions are in the same menu. Comparing how two of them judge a position is a good reminder that an evaluation is only an estimate.
Stockfish analysis on a full board
Here Stockfish drives a complete analysis board: its best moves drawn as arrows, the evaluation and line behind each candidate move, a report on every mistake in a game, and a board editor for setting up any position by hand.
Reading the evaluation
The number is in pawns, from White's point of view: +1.2 means White is about a pawn better, and -3.0 means Black is up about a piece. A value like #4 means forced mate in four. Recent Stockfish versions scale the number so that +1.0 means about a 50% chance of winning, so treat the pawn as a rough unit.
Keep two cautions in mind. First, the evaluation assumes best play from both sides, and a position rated +0.8 can still be much easier for the defender to play in practice. Second, at low depth in a sharp position the evaluation can swing wildly, so let it settle before you draw 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.
Next move calculator
Paste a position and let Stockfish find the best move.
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.
Which version of Stockfish is it?
Stockfish 19, the latest release, is available from the engine menu on the analysis board. The board opens on a smaller, faster-loading engine so the first visit is quick; pick Stockfish 19 once and it is remembered.
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. The gap is too wide to measure with an Elo rating, because no human scores enough wins or draws against it. For any practical analysis question at club level, you can treat its assessment as correct.
What does the evaluation number mean?
It is measured in pawns from White's point of view. +1.0 means White is about a pawn better, and a value like #3 means mate in three. The number always assumes both sides play the best moves available.