Open-source credits
Stockfish.js 19.0.1
Our solo opponent uses the unmodified Stockfish.js lite single-thread engine by Nathan Rugg and Chess.com, based on Stockfish by T. Romstad, M. Costalba, J. Kiiski, G. Linscott and other contributors. The lite neural network is by Chris Bao (sscg13).
The engine is free software under the GNU General Public License, version 3, without warranty. Engine level is a strength setting, not an Elo rating.
- GNU GPL version 3
- Download matching Stockfish.js source and build scripts
- Download the matching lite neural network
- Exact upstream source revision
To rebuild, extract the source archive, place the network in its src directory, install the Emscripten 6.0.9 toolchain specified in the included README, install the source package dependencies, and run npm run build-single-lite. We copy the released engine files without changing their contents; only their served filenames change.
Chess rules
Move validation uses chess.js 1.4.0 by Jeff Hlywa and contributors under its BSD-2-Clause license.
REA
Development and browser verification use the full Reverse Engineer Anything harness, copyright 2026 morluto, under the MIT license. REA tools are not part of the chess app runtime.