Legal

Open-source notices

Ironwood Chess's original application code, interface, and project artwork are licensed under the GNU General Public License, version 3 or later. The third-party components below retain their respective licenses.

7z archive decoding

Browser archive decoding uses sevenz-rust2 and lzma-rust2 by the hasenbanck contributors, licensed under Apache 2.0. The bundled sevenz reader limits decoder memory and header allocations. Apache 2.0 license · sevenz-rust2 source · lzma-rust2 source

Scid database reader

Scid import uses chess-scid-rw by Fabrice, including decoder code derived from Scid and chess code from Vendetta Chess GUI, under GPL-3.0-or-later. Ironwood bundles commit 6253187d211ed872a3b545fc251e85fec88dd8f8 with stricter handling of truncated comments.

GPLv3 license · Upstream source · Bundled source and changes

egui and eframe user interface

Ironwood Chess uses egui, eframe, and egui_extras by Emil Ernerfeldt and the egui contributors for its Rust user interface. These libraries are dual-licensed under MIT or Apache 2.0; Ironwood uses them under the MIT license.

egui website · Source for the bundled version · MIT copyright and license notice

Bundled egui default fonts are unchanged: Ubuntu Light by Dalton Maag (Ubuntu Font Licence), Hack by Source Foundry (MIT and Bitstream Vera notices), Google Noto Emoji (SIL Open Font License 1.1), and emoji-icon-font by John Slegers (MIT).

The About dialog uses the unmodified official egui logo, designed by Studio Gruhl and commissioned by Rerun.io. The logo is distributed as an asset of the egui_demo_lib package under MIT or Apache 2.0; Ironwood uses the MIT option. It identifies the UI framework used by Ironwood and does not imply endorsement.

Official logo source · Asset packaging and license declaration · Logo designer credit

Ironwood Chess

Read the complete GPLv3 license · Browse the corresponding source

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

Ironwood modifies the Stockfish.js JavaScript glue to prepare its pthread pool asynchronously before setting the thread count (2026-10-11). The engine WebAssembly and NNUE network are unchanged. The GPLv3 patch and reproducible copy step are included in the Ironwood source repository.

Lichess puzzle data

Puzzles are supplied by Lichess under the Creative Commons CC0 1.0 public domain dedication. Puzzle database and licensing · CC0 1.0 terms

Chess piece artwork

The selectable Cburnett and Merida SVG chess-piece sets are distributed without modification from the Lichess project.

Cburnett: Copyright © Colin M.L. Burnett.
Merida: Copyright © Armando Hernandez Marroquin.
License: GNU General Public License, version 2 or any later version.

Read the complete GPLv2 license

Cburnett corresponding source · Merida corresponding source · Lichess licensing table

Royal Rascals is original project artwork supplied for Ironwood Chess and is not part of the Lichess distributions above.

Undead Court is original AI-assisted project artwork directed by the Ironwood Chess project and is not part of the Lichess distributions above.

3D board

The in-game 3D board uses chess-piece and board geometry and textures from Poly Haven's Chess Set by Riley Queen for Marble and Glass, Omie's Low Poly 3D Chess/Checkers Set for Wood, and Polyy.AI's 3D Chess Sets Pack 1 for Art Deco and Egyptian. The three asset packs are published under CC0 1.0 and rendered inside egui through wgpu. The separate FEN viewer uses Three.js under the MIT license.

Poly Haven chess set · Poly Haven CC0 license · Omie's CC0 chess set · Polyy.AI CC0 chess sets · Three.js MIT license · Three.js source

Rust logo

The About dialog uses the unmodified official Rust programming language logo to identify Rust as a technology used to build Ironwood Chess. This does not imply endorsement by or affiliation with the Rust Project or Rust Foundation.

Owner: Rust Foundation.
License: Creative Commons Attribution 4.0 International.

Official logo source · CC BY 4.0 license · Rust trademark and media policy

Screenshot recognition

Uses Fenshot and ONNX Runtime Web. Recognition runs locally.

Fenshot MIT license · ONNX Runtime MIT license

PostHog browser analytics

Optional analytics use PostHog JS, licensed under Apache 2.0 and MIT. License and notices · Bundled dependency notices

Opening classification data

Opening names and ECO codes use the Lichess chess-openings dataset, released under the CC0 Public Domain Dedication.