Open-source licenses

OpeningScrim is proprietary software. It ships with, and is grateful for, the open-source components below — they are distributed unmodified under their own licenses, with license texts, checksums, and complete corresponding source offered on this page.

How the engines are integrated

The chess engines run as separate programs: WebAssembly binaries executed in their own Web Workers, communicating with the application over the UCI text protocol. The application itself is not derived from them and remains proprietary; the engine files below are conveyed to your browser unmodified under their respective licenses, which grant you the right to copy and redistribute them.

Components

Stockfish 18 lite (WebAssembly, stockfish.js)

Version: 18.0.7 (npm)
License: GPL-3.0
Copyright: © The Stockfish developers; Stockfish.js © Chess.com, LLC / Nathan Rugg
Upstream: github.com/nmrugg/stockfish.js · stockfishchess.org
License text: GPL-3.0 (Copying.txt)
Corresponding source: stockfish.js-18.0.7-src.tar.gz · stockfish-18.0.7-npm.tgz

SHA-256 of served files

stockfish-18-lite-single.js: 5243fd9b276cab7dfe3ad1d43ab9ead73568fac76468c614242977a210c4a391
stockfish-18-lite-single.wasm: a8fbc05ec6920b56d7485826dcb02c5ffd2826bcbf751cf973046f237a9096f1
stockfish-18-lite.js: 6e64f417a642c2f2a27d33c09f069522366d1bc33ed7ee8712afcc347e109af4
stockfish-18-lite.wasm: d50136919dcd90e75eb8df78b255d47d618962b670028b38961343f6eb409174

zerofish (Stockfish + Leela Chess Zero WebAssembly)

Version: 0.0.40
License: AGPL-3.0-or-later (embeds Stockfish + lc0, GPL-3.0; Eigen, MPL-2.0)
Copyright: © lichess.org contributors; engines © their respective authors
Upstream: github.com/lichess-org/zerofish · github.com/LeelaChessZero/lc0
License text: AGPL-3.0 (LICENSE.txt)
Corresponding source: zerofish-0.0.40-with-sources.tar.gz

SHA-256 of served files

zerofish.js: 47b2c6dacbf1f4bbf158eea94877bc000437bac10e2d9e6a68c23e7044e0e4d1
zerofishEngine.js: 92814f0aa6ad1e8a11518493c31ba21766efc69654a3729670f82c770ec1792d
zerofishEngine.wasm: 9f240e9175b8f449cc2b3f9e9ccd3bf01f6923d3de81c49f3d75f1bbda1331df

Maia chess neural-net weights (1100–1900)

Version: 749204cf
License: GPL-3.0
Copyright: © CSSLab, University of Toronto
Upstream: github.com/CSSLab/maia-chess
License text: GPL-3.0 (Copying.txt)
Corresponding source: maia-chess-749204cf-src.tar.gz

Reference: McIlroy-Young et al., “Aligning Superhuman AI with Human Behavior: Chess as a Model System”, KDD 2020. The weight files themselves are served unmodified — for a neural network they are the preferred form for making modifications (fine-tuning); the training pipeline is included in the source archive.

SHA-256 of served files

maia-1100.pb.gz: e1cf1cd0c96b8a4fa6a275f4b9fd54ed1ffebf9fe44641b9fceded310e9619c4
maia-1300.pb.gz: 36195f87bf4761834baa0bf87472b18509a7261a9d7d6f1a8443261369a733f2
maia-1500.pb.gz: 35ab6f20421d59e1df3b17c5a5016947af4c6761368ef84044a9a9c7619a9a00
maia-1700.pb.gz: d277eacd792d340a30abb464dc65127254e65cac57abca17facc469889b96478
maia-1900.pb.gz: e2f565f42d7cd9f122557e6dc4eb84e5bbaedceda1d404dc485d3611c7c97a12

Cburnett chess piece set (SVG artwork)

Version: chessground 10.x assets
License: BSD (triple-licensed GFDL / BSD / GPLv2+)
Copyright: © Colin M. L. Burnett
Upstream: commons.wikimedia.org (Category:SVG chess pieces) · github.com/lichess-org/chessground

Hand-drawn SVG chess pieces, triple-licensed GFDL / BSD / GPLv2+ and used here under the BSD license. Transcribed into the application source from the chessground assets, so boards render without chessground.

Newsreader typeface (web font)

Version: @fontsource-variable/newsreader 5.3.0 (Google Fonts build)
License: SIL Open Font License 1.1
Copyright: © 2020 The Newsreader Project Authors (Production Type)
Upstream: github.com/productiontype/Newsreader · fonts.google.com/specimen/Newsreader
License text: OFL-1.1 (Newsreader-OFL.txt)

Geist Sans / Geist Mono typefaces (web fonts)

Version: geist 1.7.x (npm)
License: SIL Open Font License 1.1
Upstream: github.com/vercel/geist-font

Chessground (board UI)

Version: 10.x
License: GPL-3.0-or-later
Upstream: github.com/lichess-org/chessground
License text: GPL-3.0 (Copying.txt)

Currently part of the application bundle; scheduled for replacement.

Third-party notices (permissive licenses)

Data sources

Opening statistics come from the Lichess opening explorer (lichess.org). The underlying game and puzzle databases are released by Lichess under CC0 (public domain). Thank you, Lichess.

Cloud position evaluations are provided by the Chinese Chess Cloud Database, chessdb.cn (public-domain data, courtesy of its operator).

License texts are legal documents and are provided in English only.

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