@lichess-org/stockfish-web

WebAssembly builds for Stockfish.

This package is optimized for the lichess.org website, which needs multiple builds and chess variants. It is not straight-forward to load and use.

Check out https://github.com/nmrugg/stockfish.js for a simpler browser Stockfish.

Building

# Example: Clean and make all targets with pgo and final bench signature verification
./build.py clean all --pgo --verify-bench

Use --cxx-flags to override the default emcc flags (-O3 -DNDEBUG --closure=1).

Use --ld-flags to override default linker flags (--ld-flags='-sENVIRONMENT=web,worker,node').

Check ./build.py --help for all available targets.

To avoid installing or changing your emscripten version, use ./build-with-docker.sh or ./build-with-podman.sh:

# Example: Docker clean and make all targets for node as debug with SAFE_HEAP
./build-with-docker.sh --cxx-flags='-O0 -g3 -sSAFE_HEAP' --ld-flags='-sENVIRONMENT=node' all clean

# Example: Clean and make dist targets for web with a preallocated pthread pool size of 8
./build.py --ld-flags='-sENVIRONMENT=web,worker -sPTHREAD_POOL_SIZE=8' clean dist

./build.py downloads sources to the ./fishes folder then applies diffs from the ./patches folder. Edit the Stockfish sources within ./fishes. Contribute your edits via patch file.

# Example: Update `sf_18.patch` with your commits
cd fishes/sf_18
git format-patch stockfish-web/base --stdout > ../../patches/sf_18.patch

Run locally on node

./tools/wasm-cli.ts bootstraps the emscripten module and also automatically downloads the required nnue files into the current working directory.

./build.py
node ./tools/wasm-cli.ts ./sf_18.js
uci

Sources

sf_18_smallnet (Stockfish 18 with sscg13/threat-small)

• repo: https://github.com/official-stockfish/Stockfish
• base: cb3d4ee9
• tag: sf_18 (patch includes rebase of https://github.com/sscg13/Stockfish/tree/threat-small)
• nnue: nn-4ca89e4b3abf.nnue

sf_18 (Stockfish 18)

• repo: https://github.com/official-stockfish/Stockfish
• base: cb3d4ee9
• tag: sf_18
• big nnue: nn-c288c895ea92.nnue
• small nnue: nn-37f18f62d772.nnue

sf_dev (Stockfish dev-20260609-415ff793)

• repo: https://github.com/official-stockfish/Stockfish
• base: 415ff793
• tag: stockfish-dev-20260609-415ff793
• nnue: nn-71d6d32cb962.nnue

fsf_14 (Fairy-Stockfish 14)

• repo: https://github.com/fairy-stockfish/Fairy-Stockfish
• base: a621470b
• nnues: see repo links

Older repositories kept for compatibility

stockfish-nnue.wasm

Stockfish 14 without dynamic import() in WebWorker.

stockfish.wasm and stockfish-mv.wasm

SF_classical (strongest handcoded eval) and multi-variant equivalent. No SIMD. No dynamic import() in WebWorker.

stockfish.js

Stockfish 10 in pure JavaScript or WebAssembly without shared memory.