Stockfish is the strongest chess engine that exists, open source or otherwise, and has been at or near the top of every published rating list for over a decade. It is the engine behind the analysis on almost every chess website, and the one most chess bots are built on.
It searches millions of positions per second using alpha-beta search with aggressive pruning, and evaluates them with NNUE — an efficiently updatable neural network that replaced the old hand-written evaluation function from Stockfish 12 onwards. That change was one of the largest single strength jumps in computer chess history.
On Chessy it runs compiled to WebAssembly inside your browser tab, in both single-threaded and multi-threaded builds. The multi-threaded version needs SharedArrayBuffer, which requires specific security headers; where that is unavailable the site falls back to the single-threaded build automatically.
What makes it distinctive
- ▸NNUE neural network evaluation, running entirely on your CPU
- ▸Has a strength floor — it will not play below a rating of 1320, whatever you request
- ▸Multi-threaded build available when your browser supports SharedArrayBuffer