Open-source licenses

Game engine

Game analysis and the computer opponent are powered by Rapfi, which runs on our servers and is never sent to your browser. Rapfi is licensed under the GNU General Public License v3.0 and its source code is available from the project. Its neural network weights come from rapfi-networks and are dedicated to the public domain (CC0-1.0).

• Rapfi GPL-3.0
• rapfi-networks CC0-1.0

Backgammon engine

The backgammon computer opponent is powered by GNU Backgammon (gnubg), which runs on our servers as a separate process in its own container and is never sent to your browser. GNU Backgammon is licensed under the GNU General Public License v3.0-or-later and its source code is available from the project.

• GNU Backgammon GPL-3.0-or-later

Chess engine

The chess computer opponent is powered by Stockfish, which runs on our servers as a separate process in its own container and talks to the site only over a network protocol. It is not linked with Turnpan's code and is never sent to your browser. Stockfish is licensed under the GNU General Public License v3.0 and its source code is available from the project.

• Stockfish GPL-3.0

Browser analysis engine

Post-game analysis runs in your browser, only when you open it, using stockfish.js 19.0.0 (Stockfish 19 compiled to WebAssembly by nmrugg). Stockfish and stockfish.js are licensed under the GNU General Public License v3.0. The engine files are served from this site; the license text and source notes are linked below.

• License text (GPL-3.0)
• Source notes for the served build
• stockfish.js v19.0.0
• Stockfish

Stockfish 19 / stockfish.js 19.0.0, GPL-3.0

Chess pieces

Chess pieces by Colin M.L. Burnett (Cburnett), BSD license, via Wikimedia Commons. The license text is reproduced below.

• cburnett BSD-3-Clause

Copyright (c) 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 the copyright holder 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 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 HOLDER 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.