Third-party software used by this site ====================================== Each section below names a third-party component, the licence it is used under and the notice that licence requires. Preact 10.29.8 -------------- Source: https://github.com/preactjs/preact Use: the page components (bundled) Licence: MIT The MIT License (MIT) Copyright (c) 2015-present Jason Miller Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. @preact/signals 2.11.3 and @preact/signals-core ----------------------------------------------- Source: https://github.com/preactjs/signals Use: shared state (bundled) Licence: MIT The MIT License (MIT) Copyright (c) 2022-present Preact Team Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. chess.js 1.4.0 -------------- Source: https://github.com/jhlywa/chess.js Use: the rules of chess: legal moves, check, mate and draws (bundled) Licence: BSD-2-Clause Copyright (c) 2025, Jeff Hlywa (jhlywa@gmail.com) All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Lexend ------ Source: https://github.com/googlefonts/lexend Use: the text font, self-hosted as /fonts/Lexend-Variable.woff2 Licence: SIL Open Font License 1.1 (full text at /fonts/Lexend-OFL.txt) Copyright 2018 The Lexend Project Authors (https://github.com/googlefonts/lexend), with Reserved Font Name “RevReading Lexend”. IBM Plex Mono ------------- Source: https://github.com/IBM/plex Use: the monospace font, self-hosted as /fonts/IBMPlexMono-Regular.woff2 and /fonts/IBMPlexMono-SemiBold.woff2 Licence: SIL Open Font License 1.1 (full text at /fonts/IBMPlexMono-OFL.txt) Copyright © 2017 IBM Corp. with Reserved Font Name "Plex" Chess pieces: Cburnett set -------------------------- Source: https://commons.wikimedia.org/wiki/Category:SVG_chess_pieces/Standard_transparent Use: the board's pieces, /pieces/cburnett/ Licence: BSD (chosen among GFDL-1.2+, CC BY-SA 3.0, BSD, GPL-2+) Copyright (c) 2006, Colin M. L. Burnett All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. Neither the name of Colin M. L. Burnett nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY COLIN M. L. BURNETT AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COLIN M. L. BURNETT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. Stockfish 19 ------------ Source: https://github.com/nmrugg/stockfish.js (packaging by Nathan Rugg and Chess.com of https://github.com/official-stockfish/Stockfish) Use: the computer opponent of the play page, run unmodified in its own Web Worker as /engine/stockfish-19-lite-single.js and /engine/stockfish-19-lite-single.wasm Licence: GNU General Public License version 3 (full text at /engine/Copying.txt) Stockfish is written by the Stockfish developers (see the AUTHORS file in the source archive). Its complete Corresponding Source is served beside it: /engine/source/stockfish.js-0d5dd7944f88.tar.gz /engine/source/nn-61e7af4bb97d.nnue /engine/source/README.txt Lichess puzzle database ----------------------- Source: https://database.lichess.org/#puzzles Use: the puzzles, filtered at build time Licence: Creative Commons CC0 1.0 (public domain dedication); credited by choice