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Chessblood

Open source

Licences and credits

Chessblood is built on free and open-source software and freely licensed artwork. This page credits the people behind it and tells you where to find the source code.

Stockfish 19

The chess engine behind every evaluation on this site.

Stockfish is a free, open-source chess engine developed by the Stockfish developers and contributors. It is licensed under the GNU General Public License version 3 (GPL v3).

The browser builds come from stockfish.js, Nathan Rugg's WebAssembly port of Stockfish, which is also licensed under the GPL v3. We serve the “lite” builds of stockfish.js version 19.0.1, exactly as they are published in the stockfish npm package, without modification. The lite builds use a smaller neural network made for Stockfish 19, which the stockfish.js project credits to sscg13. The optional server-side engine in our API uses the same package.

Source code. The complete corresponding source for the engine files is the stockfish.js repository at the v19.0.1 release, which builds on the official Stockfish source code. You are free to use, study, share and modify Stockfish under the terms of the GPL v3.

Files served from this site

  • /engines/stockfish-19-lite.js
  • /engines/stockfish-19-lite.wasm
  • /engines/stockfish-19-lite-single.js
  • /engines/stockfish-19-lite-single.wasm

The licence text is served next to them:

/engines/COPYING.txt

GNU General Public License, version 3. Also available at gnu.org.

Chessblood is not affiliated with or endorsed by the Stockfish project. The engine runs in your browser as a separate program; the rest of the site talks to it through the standard UCI text protocol.

Artwork and fonts

Data

Positions and puzzles that come from outside sources.

The accuracy figures follow the win-probability and accuracy method that Lichess published in 2022; the accuracy calculator shows the formulas. Game imports use the public Chess.com API and Lichess API.

Libraries in the website

Libraries in the API server

The API also uses chess.js, Zod and the stockfish package listed above.

Build tools

These packages depend on many smaller open-source libraries, each under its own licence, which travel with them. If you believe something is missing or credited wrongly, please let us know.