ChessClerk is built on other people's work. This page says whose, and under what terms. Last checked 27 July 2026.
ChessClerk includes and distributes Stockfish.js 18, a WebAssembly build of the Stockfish chess engine, which runs entirely in your browser.
Licensed under the GNU General Public License, version 3.
Stockfish is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
Complete corresponding source code:
Stockfish.js 18 © 2026 Chess.com, LLC. Based on Stockfish by T. Romstad, M. Costalba, J. Kiiski, G. Linscott and other contributors. Neural networks by Linmiao Xu (linrock). The build shipped here is unmodified.
Maia-2, a neural network trained to predict human moves at a given rating rather than to find the best move.
Licensed under the MIT License. © CSSLab, University of Toronto.
Tang, Jiao, McIlroy-Young, Kleinberg, Sen and Anderson. Maia-2: A Unified Model for Human-AI Alignment in Chess. NeurIPS 2024.
Runs the Maia model in your browser. Loaded on demand from a CDN.
Licensed under the MIT License. © Microsoft Corporation.
ChessClerk queries the public Lichess API for cloud evaluations and puzzles.
Lichess is free and open-source software, licensed under the GNU Affero General Public License v3. Its game and puzzle databases are released into the public domain under CC0.
lichess.org · database.lichess.org · github.com/lichess-org/lila
ChessClerk is not affiliated with or endorsed by Lichess.
The twelve piece images are the standard Cburnett set.
Licensed under Creative Commons Attribution-ShareAlike 3.0 Unported. Created by Cburnett, via Wikimedia Commons. Used unmodified, with no additional restrictions applied.
The attribution notice and the full text of the license are distributed with the work, as the license requires: read them here.
Hosting, authentication and storage are provided by Google Firebase. The API proxy runs on Cloudflare Workers. Neither is redistributed here; both are services ChessClerk uses.
The clerk is powered by models from Anthropic and Google, accessed over their APIs. Those models are not distributed with ChessClerk and remain the property of their providers, under their own terms of service.
The ChessClerk application code is © 2026 ChessClerk. All rights reserved.
The shared library of verified chess lines is a separate thing and is not covered by that. Positions, evaluations and plans contributed to the public library carry no author, no owner, and no restriction. Reprint what you like.
If you believe a licence is misstated or an attribution is missing, tell the clerk and it will be filed.