Made possible by open source.

Velvet uses Stockfish 18 Lite WASM, the single-thread browser build from stockfish.js 18.0.8 by Nathan Rugg / Chess.com and the Stockfish contributors. This smaller model is weaker than the full Stockfish 18 build.

Engine source and build instructions · Engine releases and corresponding source · GNU GPL v3 license

Chess rules: chess.js 1.4.0, Jeff Hlywa and contributors, BSD-2-Clause. License.

Chess piece sets, distributed by Lichess, with artwork unchanged:

• Classic (Cburnett): Colin M. L. Burnett, and Merida: Armando Hernandez Marroquin — GPL v2 or later, distributed here under GPL v3.
• Chessnut: Alexis Luengas — Apache 2.0.
• Spatial: Maurizio Monge — MIT.

Artwork sources and notices.

Club bot and Mischief bot are local chess algorithms, not ChatGPT. Stockfish assistance uses the same Stockfish 18 Lite build in a separate worker. Illegal game actions are exported as annotated PGN comments.

Sound recordings: Kenney Impact Sounds and Interface Sounds, CC0. The 18 effects include remixed percussion and an original synthesized Brilliant chime. Standard uses a 90 kbps AAC target; High uses 320 kbps MP3. The original Ogg recordings range from 96–240 kbps: the higher delivery bitrate preserves the new mix but does not restore lost source detail. Audio sources and encoding notes · Impact license · Interface license.

Velvet's application code is available under GNU GPL v3. Download the complete source or download a single self-contained HTML file.

Motion follows your display's animation scheduler. The FPS indicator measures delivered animation callbacks, rather than the monitor's configured refresh rate. Browser scheduling, power modes, and device performance can reduce the achieved rate.