Open Source Licences
The chess engines chessy.uk is built on, and your rights to their source
chessy.uk runs its chess engines in your browser, not on our servers. Choosing an opponent downloads that engine to your device and runs it locally. Most of these engines are free software released under copyleft licences, which give you the right to obtain their source code — including any changes we made.
Everything below is listed with its licence and a link to the source. Where we ship a modified build, we host the modified source ourselves so it stays matched to the exact binary you receive.
Chess engines
Texel1.08
GPL v3.0 or laterModified by us: compiled to WebAssembly, single-threaded, with pondering disabled and unbounded searches capped. Full changes are described in the source archive.
Stockfish10, 11, 17.1, 18 (full and Lite)
GPL v3.0Leela Chess Zero
GPL v3.0Reckless0.10.0
AGPL v3.0Rodent IV
GPL v3.0Koivisto8.0
GPL v3.0Lozza
MITLicence texts
The full terms are published by the Free Software Foundation: GPL v3.0 and AGPL v3.0. The MIT licence text is included in the Lozza repository linked above.
Chessy itself
The engines run in isolated Web Workers and exchange only plain UCI text with the rest of the site. They are not linked into the application, so the copyleft terms above cover the engines and our changes to them — not chessy.uk's own code, which is not open source.
Something missing?
If you believe an attribution is wrong or a source link is broken, please tell us through the contact form and we will correct it.