Bundles Stockfish 18 as packaged native engine, single dependency with coroutine-friendly suspend API for setPosition/search, singleton instance, thread-safe serialized calls, Full vs Lite NNUE variants.
The only Kotlin Multiplatform library that bundles the Stockfish 18 chess engine as a native library for JVM, Android, iOS, and WebAssembly. Add one dependency and call the engine from common code: no manual binaries, no UCI subprocess wiring, no per-platform setup.
Stockfish is compiled from source and packaged for every target, so consumers ship a working engine with a single Gradle coordinate.
// Full — includes both large and small NNUE networks
implementation("fr.axl-lvy:stockfish-multiplatform:<version>")
// Lite — small NNUE network only, much smaller download size
implementation("fr.axl-lvy:stockfish-multiplatform-lite:<version>")
getStockfish() and search() are suspend functions, so call them from a coroutine:
suspend fun bestMove(): String {
val engine = getStockfish()
engine.setPosition(fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1")
val result = engine.search(depth = 20)
return result.bestMove // e.g. "e7e5"
}
getStockfish() returns a shared singleton, so most apps never close it. If you do call close(),
the next getStockfish() creates a fresh engine.
All targets are implemented and exercised in CI on every change.
Both modules expose the same API — the only difference is the bundled NNUE network:
| Full | Lite | |
|---|---|---|
The full variant re-evaluates positions with the large network when the small network's evaluation is uncertain, giving it a slight accuracy edge. The lite variant skips this and always uses the small network, resulting in a much smaller artifact.
Stockfish uses multi-threaded WebAssembly, which requires the browser to have SharedArrayBuffer enabled. Browsers only expose SharedArrayBuffer when the page is served with specific HTTP headers.
Kotlin/WASM with webpack — create webpack.config.d/headers.js in your module directory:
if (config.devServer) {
config.devServer.headers = Object.assign(config.devServer.headers || {}, {
"Cross-Origin-Opener-Policy": "same-origin",
"Cross-Origin-Embedder-Policy": "credentialless"
});
}
Production — configure your web server to add the same headers to all responses:
Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: credentialless
These headers are a browser requirement for any multi-threaded WebAssembly application, not specific to this library.
Runtime download: on WebAssembly the Stockfish engine is fetched at startup from the public CDN
https://unpkg.com/stockfish@18.0.5/.... The firstgetStockfish()therefore requires network access, and your Content-Security-Policy must allowunpkg.com. This applies only to the WebAssembly target; JVM, Android, and iOS bundle the engine natively.
| Platform | Targets | How the engine runs |
|---|
| JVM | Linux, macOS, Windows (x86_64) | bundled native library via JNI |
| Android | arm64-v8a, armeabi-v7a, x86_64 | bundled native library via JNI |
| iOS | arm64 device, arm64 + x64 simulator | bundled static library via cinterop |
| WebAssembly | browser (wasmJs) | Web Worker; engine fetched from a CDN at startup |
| NNUE networks |
| Large + small |
| Small only |
| Strength | Maximum | Slightly weaker |
| Binary size | Larger | Smaller |
getStockfish() enforces this by returning the same instance on subsequent calls, unless the previous one was closed.setPosition, search, setOption, postMessage) is mutex-serialized and safe to call from any coroutine. stop() and unsafePostMessage() are intentionally unguarded so they can be called while the mutex is held (e.g. to interrupt a search).stop() usage: Because search() holds the mutex until the engine emits bestmove, stop() must be called from a separate coroutine or thread.close() behavior: After close(), isClosed returns true and the next call to getStockfish() creates a fresh engine instance.setPosition, setOption, postMessage, or search after close() throws IllegalStateException. If close() is called while a search() is in flight, that search() throws IllegalStateException instead of returning a result.Surfaced from shared tags and platforms — no rankings paid for.