Source code

Chessvera is free software under the GNU General Public License, version 3.

Why Chessvera is open source

Chessvera includes the Stockfish chess engine, which is licensed under the GNU GPL version 3. An app that includes GPL code must itself be shared under the GPL, so the whole Chessvera app is licensed under the GNU General Public License, version 3 (GPLv3). We are happy with that: Chessvera is built on a lot of open-source work, listed below.

What you may do

The GPLv3 gives everyone who has the app these freedoms:

• Use the app for any purpose.
• Study how it works, with the complete source code.
• Share copies with others.
• Change it and share your changed version, as long as you share it under the GPLv3 too, with its source code.

Chessvera 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 licence for details. Buying Chessvera Pro in the App Store or Google Play does not change any of these rights. The GPL covers the code, not the name: please give a changed version its own name and icon, so nobody confuses it with Chessvera.

Where to get the source

Each version released in the stores will be tagged in the repository with its version number, so you can get the exact source of the version on your phone. Until then, or if the link ever stops working, email support@chessvera.com and we will send you the complete source code of any released version, free of charge. The app's About screen (Settings, About and licences) lists every licence in full.

Credits: chess engine

Chessvera includes and is powered by Stockfish 19, a free and open-source chess engine by the Stockfish developers, licensed under the GPLv3. Chessvera is not affiliated with or endorsed by the Stockfish project. Stockfish's neural networks are trained on data provided by the Leela Chess Zero project, made available under the Open Database License (ODbL). The mobile build uses a small network and a patch by sscg13 and Niklas Fiekas, packaged by Lichess in multistockfish (GPLv3), which also includes Fairy-Stockfish (GPLv3).

Chess libraries

• dartchess by Lichess (GPLv3): chess rules and notation.
• chessground by Lichess (GPLv3): the chessboard, with modified coordinates.
• Flutter and its packages (BSD, MIT and Apache licences).

Boards and pieces

• Wood, marble and other textured boards: from lichess.org, by the lila authors and pirouetti (AGPLv3 or later).
• Piece sets: cburnett (Colin M.L. Burnett, GPLv2+), merida (Armando Hernandez Marroquin, GPLv2+), chessnut (Alexis Luengas, Apache-2.0), fantasy, spatial and celtic (Maurizio Monge, MIT), mpchess (Maxime Chupin, GPLv3+), rhosgfx (RhosGFX, CC0), firi (James Faure, CC BY 4.0), totoy (Kosal Sen, CC BY 4.0), kiwen-suwi (neverRare, CC BY 4.0), shapes (flugsio, CC BY-SA 4.0).
• The Walnut maple board, app icon and coach icon are Chessvera's own artwork.

Icons and sounds

• Icons: Font Awesome Free by Fonticons, Inc. (icons CC BY 4.0, font SIL OFL 1.1).
• Wood move sounds made from recordings by JJTaynos and MattyCauldron on Freesound (CC0).
• Tap sound: "Billiard balls single hit-dry" by juskiddink (CC BY 4.0), shortened and faded.
• Win chime from FlawChess (CC0).
• Other sounds are Chessvera's own synthesis.

Data

• Puzzles from the Lichess puzzle database (CC0).
• Live games, the opening explorer and game imports use the public APIs of Lichess and Chess.com. Chessvera is not affiliated with either.
• Opening courses and lessons are written for Chessvera.