stockfish/README.md

The Stockfish chess engine in Web Assembly (WASM)

### Stockfish.js

<a href="https://github.com/nmrugg/stockfish.js">Stockfish.js</a> is a WASM implementation by Nathan Rugg of the <a href="https://github.com/official-stockfish/Stockfish">Stockfish</a> chess engine, for [Chess.com's](https://www.chess.com/analysis) in-browser engine.

Stockfish.js is currently updated to Stockfish 18.

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 (>100MB) and will only run in browsers with the proper <a href=https://web.dev/articles/cross-origin-isolation-guide>CORS headers</a> applied. This engine is recommended if possible.
    * Files: [`stockfish-18.js`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18.js) & [`stockfish-18.wasm`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18.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-18-single.js`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-single.js) & [`stockfish-18-single.wasm`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-single.wasm)
 * The lite mult-threaded engine:
    * This is the same as the first multi-threaded but much smaller (≈7MB) and quite a bit weaker. This engine is recommended for mobile browsers when CORS is available.
    * Files: [`stockfish-18-lite.js`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-lite.js) & [`stockfish-18-lite.wasm`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-lite.wasm)
 * The lite single-threaded engine:
    * Same as the first single-threaded engine but much smaller (≈7MB) and quite a bit weaker. This engine is recommended for mobile browsers that do not support CORS.
    * Files: [`stockfish-18-lite-single.js`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-lite-single.js) & [`stockfish-18-lite-single.wasm`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-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 (≈10MB). This engine should only be used as a last resort.
    * File: [`stockfish-18-asm.js`](https://github.com/nmrugg/stockfish.js/releases/download/v18.0.0/stockfish-18-asm.js)

The WASM Stockfish engine will run on all modern browsers (e.g., 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 <a href=../../tree/Stockfish16>Stockfish.js 16 branch</a>. The ASM-JS engine will run in essentially any browser/runtime that supports JavaScript. For an engine that supports chess variants (like 3-check and Crazyhouse), see the <a href=../../tree/Stockfish11>Stockfish.js 11 branch</a>.

### API

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

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");`).

### Compiling

You need to have <a href="https://emscripten.org/docs/getting_started/downloads.html">emscripten `3.1.7`</a> 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`.

### Examples

To learn how to use the engine in your own projects, see the <a href="https://github.com/nmrugg/stockfish.js/tree/master/examples">examples folder</a>.

### Thanks

- <a href="https://github.com/official-stockfish/Stockfish">The Stockfish team</a>
- <a href="https://github.com/exoticorn/stockfish-js">exoticorn</a>
- <a href="https://github.com/ddugovic/Stockfish">ddugovic</a>
- <a href="https://github.com/niklasf/">niklasf</a> <a href="https://github.com/niklasf/stockfish.js">stockfish.js</a>, <a href="https://github.com/niklasf/stockfish.wasm">stockfish.wasm</a>, and <a href="https://github.com/lichess-org/stockfish-web">stockfish-web</a>
- <a href="https://github.com/hi-ogawa/Stockfish">hi-ogawa</a>
- <a href="https://github.com/linrock">linrock</a>
- <a href="https://www.chess.com/">Chess.com</a> for sponsering development of Stockfish.js

See <a href="https://raw.githubusercontent.com/nmrugg/stockfish.js/master/AUTHORS">AUTHORS</a> for more credits.

### License

(c) 2026, Chess.com, LLC
GPLv3 (see <a href="https://raw.githubusercontent.com/nmrugg/stockfish.js/master/Copying.txt">Copying.txt</a>)