Software licenses and engine source

Stockfish chess engines

Stockfish is distributed under the GNU General Public License version 3. Source downloads are available here without an account or payment, including the source and build scripts for the versions we distribute.

Build instructions and distribution details · Versions and checksums

Stockfish SF_classical runs as a standalone GPL UCI worker. Its complete readable bootstrap source and independent-client instructions accompany the unchanged vendor sources and license.

The SF11 bootstrap supplied by ChessExpert.io is also available as readable source, under GPL version 3 or later.

The SF19 Lite single-threaded bootstrap is supplied as readable source, under GPL version 3 or later. Its NNUE input accompanies the upstream source archive.

YOLOv5 board detector

GPL version 3 permits commercial use. The author’s own training contributions and model rights are provided under GPL-3.0-only; upstream and third-party rights remain effective. Recipients may copy, modify and redistribute covered material under GPL, with the required notices and Corresponding Source.

Download editable model source · Full GPL license · Attribution and distribution notices · Model provenance and checksums

The source package contains the maintained editable inference graph, named tensors and rebuild tools, verified to reproduce the distributed files exactly. It reconstructs the inference program; the original training checkpoint and exact upstream revision have not been recovered. Historical upstream reference.

Libraries, graphics and fonts

• Library license texts and copyright notices and dependency versions.
• Graphics, icons, font and opening-data credits.
• Chess pieces by Cburnett and Rfc1394, adapted by Stefan Haack, under CC BY-SA 3.0.
• Font Awesome Free icons by Fonticons, Inc., under CC BY 4.0; code under MIT.
• IBM Plex Sans by IBM and Cormorant Garamond by the Cormorant Project Authors, under the Plex OFL and Cormorant OFL.