Built on open-source chess
Stockfish 19
This trainer uses the unmodified Stockfish.js 19.0.0 lite single-threaded browser build by Nathan Rugg / Chess.com and the Stockfish contributors. The engine runs on your device.
GNU GPL v3 licence · Download corresponding source and build scripts · Upstream source revision
The upstream build instructions describe Emscripten and the evaluation networks needed to reproduce the engine.
Chess rules & pieces
chess.js 1.4.0 provides move validation and game state. BSD-2-Clause licence.
The site's existing SVG pieces come from python-chess. Piece credits · Licence.
Trainer source
The new trainer interface and engine bridge are provided under GNU GPL v3 or later. This grant covers the trainer files listed here, not other site content or branding.