The world's strongest chess engine: free, online, no download required.
Stockfish is the undisputed king of chess engines. Since its creation in 2008, Stockfish has dominated computer chess championships and become the standard tool for chess analysis worldwide. With an estimated ELO rating over 3500—far beyond any human capability—Stockfish provides the same analytical power used by world champions and grandmasters.
Our platform uses Stockfish 19 to power our chess calculator, game analyzer, and AI opponents. Free to use—no downloads, no registration required.
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Stockfish is a free, open-source chess engine originally derived from Glaurung, created by Tord Romstad. The name "Stockfish" is a Norwegian word for dried cod, a nod to the engine's Norwegian origins. Since 2008, hundreds of developers have contributed to making Stockfish the most powerful chess analysis tool in existence.
Stockfish is open source, which has fueled its rapid development — hundreds of contributors have improved the engine over the years. This community-driven approach is why it consistently outperforms commercial alternatives and powers top chess platforms worldwide.
Stockfish's strength is almost incomprehensible. To put it in perspective:
The latest version achieves an estimated rating over 3500 on the CCRL rating list. This makes it the strongest chess entity in history.
The highest official FIDE rating ever achieved by a human, reached in May 2014. Still over 600 points below Stockfish.
Elite human players. Stockfish would beat them 99%+ of the time.
A 600-point ELO difference means the higher-rated player is expected to win virtually every game. That is why games between strong humans and top engines are now usually played at material odds, with the engine starting a pawn or a piece down.
Stockfish combines two powerful technologies to achieve its incredible strength:
At its core, Stockfish uses alpha-beta pruning, an optimized version of the minimax algorithm. It builds a tree of possible moves, following the critical lines 20 or more half-moves deep, and prunes branches that can't possibly be better than already-found alternatives. Modern Stockfish searches millions of positions per second.
Since Stockfish 12 (2020), the engine has used NNUE (Efficiently Updatable Neural Network) for position evaluation. This neural network was trained on billions of positions and provides nuanced positional understanding that traditional hand-crafted evaluation functions couldn't match.
The combination of deep search and neural evaluation creates the strongest chess engine ever built. Our chess calculator uses this same technology for deep position analysis.
In December 2017, DeepMind's AlphaZero made headlines by defeating Stockfish 28-0 (with 72 draws) in a 100-game match. AlphaZero used pure neural network evaluation with Monte Carlo Tree Search and no traditional chess knowledge.
However, important context: AlphaZero faced Stockfish 8, an older version without NNUE. The match also used conditions that disadvantaged Stockfish (limited hash memory, no opening book).
Today's Stockfish 19 with NNUE incorporates neural network evaluation while keeping the powerful classical search. AlphaZero was never released or developed further, but Leela Chess Zero, an open-source engine built on the same method, has met Stockfish in many Top Chess Engine Championship superfinals, and Stockfish has won most of them. For the wider story from Deep Blue onwards, read how AI plays chess.
Our platform uses different Stockfish versions for different purposes:
For most users, Stockfish 19 is the right choice. It's what powers our game analyzer and position calculator.
You don't need to download anything to use Stockfish. Our platform provides several ways to access its power:
Our chess calculator runs Stockfish 19 in your browser. Set up any position, click analyze, and see the best move, evaluation score, and alternative lines. For the engine with its full depth and line controls, use Stockfish online. Pro members can also upload an image from a book, video or article, and the Position Reader sets the position up automatically.
Our chess analysis board, part of Pro, reviews every move in your game, classifying each as brilliant, good, inaccuracy, mistake, or blunder. You'll see exactly where you went wrong and what you should have played.
Our 11 chess bots are powered by Stockfish with adjustable strength. From 1400 up they use Stockfish's own UCI_Elo limit; below that, where UCI_Elo cannot go, they combine a low skill level, a shallow search and a share of random moves. Together they run from 400 ELO (complete beginner) to 3650 ELO (full Stockfish strength).
Watch Stockfish play against itself to see perfect chess. Our calculator features an "AI vs AI" mode where you can observe the engine's strategies and learn from its choices.
When Stockfish analyzes a position, it gives an evaluation score. Here's what the numbers mean:
Generally, an advantage of +1.0 is significant, +2.0 is usually winning with accurate play, and +3.0 or more is nearly always decisive.
Stockfish isn't just for analysis. It's a powerful training tool:
The key is using Stockfish to learn, not just to find answers. When the engine suggests a move you didn't see, ask yourself: "Why is this better? What did I miss?"
This depends entirely on context:
All major chess platforms strictly prohibit engine use during rated play. Fair play policies detect engine-like moves and result in account bans. Use Stockfish ethically — for learning and improvement, never for cheating.
Stockfish is a free, open-source chess engine that has dominated computer chess since 2008. It consistently ranks as the world's strongest chess engine with an estimated ELO over 3500—far stronger than any human player, including Magnus Carlsen.
Stockfish is dramatically stronger than any human. Magnus Carlsen's peak rating was 2882. Stockfish 19 is rated over 3500. This 600+ point gap means Stockfish would win virtually 100% of games against the world champion.
Yes! Our chess calculator runs Stockfish 19 directly in your browser via WebAssembly. Get deep analysis, game reviews, and AI opponents with no registration or payment required.
NNUE (Efficiently Updatable Neural Network) is a neural network evaluation system integrated into Stockfish since version 12. It combines traditional alpha-beta search with neural network position evaluation, dramatically improving playing strength and positional understanding.
Modern Stockfish with NNUE is extremely competitive with AlphaZero. In their famous 2017 match, AlphaZero beat an older Stockfish version. Today's Stockfish 19 is much stronger and would likely match or exceed AlphaZero's level.
Each version brings improvements. Stockfish 19 (latest) features enhanced NNUE evaluation, better search algorithms, and UCI_Elo for accurate strength limiting. Older versions like Stockfish 11 are still useful for community puzzles that allow non-standard positions.
Absolutely! Use Stockfish for game analysis to find mistakes, position evaluation to understand complex positions, and training against adjustable-strength opponents. Our platform uses Stockfish for all analysis and AI bots.
Stockfish 19's estimated ELO is over 3500 on the CCRL rating list. For comparison, the highest human rating ever was Magnus Carlsen's 2882. No human can compete with Stockfish at full strength.
Stockfish uses alpha-beta search with iterative deepening to explore millions of positions per second. The NNUE neural network evaluates each position's strength. Combined, this finds the objectively best moves in most positions.
Using any chess engine during rated online or over-the-board games is cheating and will get you banned. However, using Stockfish for post-game analysis, training, and learning is completely legitimate and encouraged.
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