Credits

Puzzles

• Most puzzles come from the Lichess puzzle database, free for any use (CC0).
• Opening names and lines: lichess-org/chess-openings (CC0).
• Classic problems: chess problem collections of the 19th century, in the public domain. Their solutions were checked with the Stockfish engine.

Software

• The site runs on Listudy by Arne Vogel, free software under the AGPL-3.0 licence.
• This site changes Listudy. As the licence asks, the source code of the version running here can be downloaded: source code (tar.gz).
• Board: chessground (GPL-3.0). Move rules: chess.js (BSD-2-Clause).
• Solutions checked with Stockfish (GPL-3.0).

Pieces and fonts

• Chess pieces: "cburnett" by Colin M.L. Burnett, CC BY-SA 3.0.
• Fonts: Rubik, Bricolage Grotesque and Atkinson Hyperlegible, under the SIL Open Font License.