Stockfish.js is a WASM implementation by Nathan Rugg of the Stockfish chess engine, currently used by Chess.com for in-browser engine use.

Stockfish.js is currently updated to Stockfish 16.1.

This edition of Stockfish.js comes in five flavors:

• The large multi-threaded engine:
  • This is strongest version of the engine, but it is large (≈66MB) and will only run in browsers with the proper CORS headers applied. This engine is recommended if possible.
  • Files: stockfish-16.1.js & stockfish-16.1.wasm
• The large single-threaded engine:
  • This is also large but will run in browsers without CORS headers; however it cannot use multiple threads via the UCI command setoption name Threads. This engine is recommended if CORS support is not possible.
  • Files: stockfish-16.1-single.js & stockfish-16.1-single.wasm
• The lite mult-threaded engine:
  • This is the same as the first multi-threaded but much smaller (≈6MB) and quite a bit weaker. This engine is recommended for mobile browsers when CORS is available.
  • Files: stockfish-16.1-lite.js & stockfish-16.1-lite.wasm
• The lite single-threaded engine:
  • Same as the first single-threaded engine but much smaller (≈6MB) and quite a bit weaker. This engine is recommended for mobile browsers that do not support CORS.
  • Files: stockfish-16.1-lite-single.js & stockfish-16.1-lite-single.wasm
• The ASM-JS engine:
  • Compiled to JavaScript, not WASM. Compatible with every browser that runs JavaScript. Very slow and weak. Larger than the lite WASM engines (≈9MB). This engine should only be used as a last resort.
  • File: stockfish-16.1-asm.js

The ASM-JS engine will run in any browser that supports JavaScript. The WASM Stockfish.js 16.1 will run on all modern browsers (Chrome/Edge/Firefox/Opera/Safari) on supported system (Windows 10+/macOS 11+/iOS 16+/Linux/Android), as well as supported versions of Node.js. For slightly older browsers, see the Stockfish.js 16 branch. For an engine that supports chess variants (like 3-check and Crazyhouse), see the Stockfish.js 11 branch.

In the browser, it is recommended to use the engine via Web Workers. See examples/loadEngine.js for a sample implementation.

You can also run Stockfish.js directly from the command line with Node.js 14.4+. You may need to add some command line flags to get it to run:

node src/stockfish.js

Stockfish.js can be found in the npm repository and installed like this: npm install stockfish.

If you want to use it from the command line, you may want to simply install it globally: npm install -g stockfish. Then you can simply run stockfishjs.

In Node.js, you can either run it directly from the command line (i.e., node src/stockfish.js) or require() it as a module (i.e., var stockfish = require("stockfish");).

You need to have the emscripten compiler installed and in your path. Then you can compile Stockfish.js with the build script: ./build.js. See ./build.js --help for details. To build all flavors, run ./build.js –all.

There are examples in the examples folder. You will need to run the examples/server.js server to view the client-side examples. Then you can test out a simple interface at http://localhost:9091/ or a more complete demo at http://localhost:9091/demo.html.

There are also examples of how to use Stockfish.js via Node.js.

• The Stockfish team
• exoticorn
• ddugovic
• niklasf stockfish.js & stockfish.wasm
• hi-ogawa
• linrock

See AUTHORS for more credits.

(c) 2024, Chess.com, LLC GPLv3 (see Copying.txt)