Strong open source chess variant engine

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Open source

Free and accessible for everyone

Fairy-Stockfish is published under the GPLv3 license. Its code can be changed and shared using the same license.

Code on GitHub


Support for user-defined variants

Fairy-Stockfish supports playing custom variants by defining game rules via a configuration file.

Variant configuration


Support for NNUE

Efficiently updatable neural networks (NNUE) can significantly enhance playing strength.

NNUE evaluation


Fairy-Stockfish is a chess variant engine derived from Stockfish designed for the support of fairy chess variants and easy extensibility with more games.


It can play various regional, historical, and modern chess variants such as

Playing strength

Despite Fairy-Stockfish’s generality the playing strength is on a very high level in almost all supported variants, especially when using NNUE. To only name a few it is the world’s strongest engine in Janggi, Crazyhouse, S-Chess, etc.


For compatibility with graphical user interfaces Fairy-Stockfish supports the UCI, UCCI, USI, UCI-cyclone, and CECP/XBoard protocols.

Latest Posts

New website

This website just came to life today. It is still under construction, but hopefully will be a useful addition to existing documentation. If you find a mistake, have a suggestion for improvement, or are just curious about how this website is built, you can have a look at its code repository.

Fairy-Stockfish 14.0.1 XQ

A new version of Fairy-Stockfish is available, see the release notes.

Fairy-Stockfish 14

A new version of Fairy-Stockfish is available, see the release notes.