Engine Asset Compliance

Chessiro uses Stockfish 19 for browser-side chess analysis. Stockfish is GPLv3 software. This page gives the license, source, and artifact details for the engine files served by Chessiro.

Ten WebAssembly builds are served — five engine variants, each with its glue script. Your browser loads whichever one it supports: multi-threaded where SharedArrayBuffer is available, single-threaded otherwise, with a no-SIMD build as a last resort. All of them embed the same evaluation network (nn-61e7af4bb97d.nnue) and play identically at equal node counts.

Distributed Engine Files

• sf19-mt-relaxed.js
• sf19-mt-relaxed.wasm
• sf19-mt.js
• sf19-mt.wasm
• sf19-st-relaxed.js
• sf19-st-relaxed.wasm
• sf19-st.js
• sf19-st.wasm
• sf19-st-nosimd.js
• sf19-st-nosimd.wasm
• chessiro-batch-worker.js

License And Source

The engine builds are Emscripten compilations of the upstream Stockfish sources. They differ from a stock build only at the WebAssembly entry point: commands sent during a search are queued until bestmove, and malformed input answers bestmove (none) rather than exiting the process, which a browser tab cannot recover from. The search and evaluation are unmodified.

chessiro-batch-worker.js is Chessiro wrapper code, served as source alongside the engine. It runs an engine build as a nested Web Worker and implements Chessiro's FEN batch protocol around the UCI interface.

To request the corresponding source for these builds, including the upstream commit and build flags, email support@chessiro.com.

• GPLv3 license
• Source notice
• Asset manifest
• Stockfish source repository