Legal

Open-source notices

Ironwood Chess includes the following third-party open-source component. These notices apply to that component, not to the original Ironwood Chess application code or artwork.

Stockfish.js 19

The chess engine delivered by this site is the full, multithreaded Stockfish.js 19 WebAssembly build with its embedded NNUE evaluation network.

Stockfish.js: Copyright © 2026 Chess.com, LLC. WebAssembly implementation by Nathan Rugg and contributors.
Stockfish: Copyright © the Stockfish developers and contributors.
License: GNU General Public License, version 3.
Distributed package: stockfish@19.0.0, Stockfish.js release v19.0.0, commit 9cb3e50.
Upstream engine: Stockfish 19, commit edb0d9d.

Read the complete GPLv3 license

Browse the exact corresponding source · Download corresponding source

Browse the exact upstream Stockfish source · Download upstream source

This distribution does not modify the Stockfish.js engine files supplied by the pinned npm package.

Ironwood Chess

Except for the open-source component identified above, the Ironwood Chess application, interface, original code, branding, and artwork are proprietary. Use of the hosted application is permitted; no license to copy, modify, or redistribute its proprietary components is granted.