Credits

Chess engines

• Stockfish by the Stockfish developers (source, GPL-3.0), with its NNUE evaluation networks. It reviews every game, plays the engine opponents and runs the calibration ladder; the ladder's ratings are on Stockfish's own UCI_Elo scale. The site runs the unmodified program; its source is at the link.
• 4pchess by obryanlouis (MIT licence), the search behind four-player game reviews. A copy adapted to free-for-all scoring is kept in engines/four with its original licence.

Formulas and ideas from Lichess

From Lichess, the free and open-source chess server (lila, AGPL-3.0). We reimplemented these; the method and the constants are theirs:

• Winning chances from an engine score: 50 + 50 · (2 / (1 + e−0.00368208·cp) − 1).
• Move accuracy from the drop in winning chances (103.1668 · e−0.04354·drop − 3.1669), and game accuracy as the mean of a volatility-weighted mean and a harmonic mean (how Lichess explains it).
• Inaccuracy, mistake and blunder thresholds: a drop of 0.1, 0.2 and 0.3 in winning chances.
• Rating categories: a separate rating per time control (bullet, blitz, rapid, classical, judged by base time plus 40 × increment) and per variant.
• Puzzles taken from real games' tactical moments, each with its own rating.

KilobyteChess is not affiliated with Lichess.

Other ideas we borrowed

• Four-player chess as a game - the fourteen-square board with the corners cut off, free-for-all on points and two-against-two teams - was made popular by Chess.com. Its rules are written out afresh in arena_sdk/arena/four.py.
• Move-grade badges on the board (best, brilliant, mistake and so on) and the promotion picker that drops out of the square follow Chess.com's idea. The badges and picker are our own drawings.
• Elo ratings by Arpad Elo, with K-factors in the way FIDE uses them.

KilobyteChess is not affiliated with Chess.com. Chess.com is a trademark of its owners.

Libraries

• python-chess by Niklas Fiekas (GPL-3.0): move generation, rules, variants and PGN, on the server and for every uploaded bot.
• Django, Channels and Daphne (BSD-3-Clause): the website and its live connections.
• PyTorch and NumPy (BSD-3-Clause): KiloNet's network and its training data.
• Uvicorn (BSD-3-Clause), Gunicorn (MIT), psycopg (LGPL-3.0) and channels-redis (BSD-3-Clause).

Fonts

Piece sets, cut down to the twelve chess symbols and renamed as their licences ask (details in static/fonts/pieces/LICENSES.md):

• Modern - from DejaVu Sans (Bitstream Vera licence).
• Elegant - from Noto Sans Symbols 2 (SIL Open Font Licence 1.1).
• Newspaper - from GNU FreeFont FreeSerif (GPL-3.0 or later, with the font embedding exception).
• Pixel - from GNU Unifont 15.1 (GPL-2.0 or later with the font embedding exception, or SIL OFL 1.1).

Text fonts, served by Google Fonts under the SIL Open Font Licence: Rajdhani, Inter, Lato, Merriweather, Source Serif, Orbitron, Share Tech Mono, JetBrains Mono, Atkinson Hyperlegible, Comic Neue (dyslexia-friendly), IBM Plex Sans.

Picture piece sets

From the piece sets Lichess publishes (lila/public/piece), used unchanged. Licence notes are kept with the files in static/pieces/LICENSES.md.

• Chessnut by Alexis Luengas - Apache 2.0.
• Pirouetti by pirouetti - AGPL-3.0 or later.
• Shapes by flugsio - CC BY-SA 4.0.
• Copper & Cream by RhosGFX - CC0 1.0.
• Fantasy by Maurizio Monge - MIT.
• Kiwen Suwi by neverRare - CC BY 4.0.
• Letters by usolando - AGPL-3.0 or later.
• Firi by James Faure - CC BY 4.0.
• Totoy by Kosal Sen - CC BY 4.0.
• Papercut by Nikolay Anzarov - CC BY 4.0.

Landscape photographs

From Wikimedia Commons, scaled down, otherwise unchanged. Notes in static/backdrops/LICENSES.md.

• Geiranger fjord: Fiordo de Geiranger desde Flydalsjuvet, Noruega, 2019-09-07, DD 59.jpg by Diego Delso - CC BY-SA 4.0.
• Dead Vlei desert: Dead Vlei, Sossusvlei, Namibia, 2018-08-06, DD 086.jpg by Diego Delso - CC BY-SA 4.0.
• Glen Coe rainbow: Glen Coe Rainbow.jpg by Colin - CC BY-SA 4.0.
• Salt flats of Uyuni: Isla del Pescado, Salar de Uyuni, Bolivia, 2016-02-04, DD 42.JPG by Diego Delso - CC BY-SA 4.0.
• Lake Titicaca dawn: Amanecer en el lago Titicaca, Puno, Perú, 2015-08-01, DD 01.JPG by Diego Delso - CC BY-SA 4.0.
• Wilderness: Alone in the unspoilt wilderness (Unsplash).jpg by David Marcu davidmarcu - CC0.
• Poppy field: Field of Iceland poppies in the flower garden near Cheomseongdae Observatory in Gyeongju South Korea.jpg by Basile Morin - CC BY-SA 4.0.
• Paddy fields: Green and luminous paddy fields under dark clouds, in Don Det.jpg by Basile Morin - CC BY-SA 4.0.
• Berchtesgaden Alps: Berchtesgaden 02.jpg by Dmytro Balkhovitin - CC BY-SA 4.0.
• Savanna sunset: Crepuscular rays at Sunset near Waterberg Plateau.jpg by Alchemist-hp (www.pse-mendelejew.de) - FAL.

The server

PostgreSQL, Redis, nginx, bubblewrap (every uploaded bot runs inside it), Let's Encrypt and Ubuntu.