Show HN: Cb2026, a Rust chess engine that revisits a 2004 world-record project

Hi HN, I'm Carlos. In 2004 Colin Frayn and I ran ChessBrain, a distributed chess computer that played a game against GM Peter Heine Nielsen using machines volunteered from around the world. It set the Guinness World Record for the largest networked chess computer. Some ideas from that project stayed with me, so I created cb2026 (ChessBrain 2026) to explore them.

cb2026 is a chess engine written from scratch in Rust. It speaks UCI and XBoard, so it runs in En Croissant, Cute Chess, XBoard and similar GUIs. It has Lazy SMP search, Syzygy tablebase probing, Polyglot opening books, Chess960, and an NNUE evaluation network trained on its own games.

Strength: about 3379 ± 21 on the CCRL Blitz scale, from 5,600 games against seven rated engines. Its original hand-crafted evaluation rated 2782, and each NNUE generation improved on that.

I wanted it to be easy to learn from as well as strong:

- Every technique can be switched off. An interactive shell lets you play it, watch it think depth by depth, and toggle things like null-move pruning to see what each one does. - docs/elo-ledger.md records how much Elo each technique gained. - A companion book, "Building a Chess Engine in Rust", has a chapter for each stage, from board representation and move generation to NNUE. Each chapter covers the idea, the real code and what it measured. It's free online, as a PDF or as an EPUB: https://cjus.github.io/chessengine/

It also has strength levels that blunder about as often as Lichess players of a given rating do.

License is MIT or Apache-2.0. The one exception: release binaries include Syzygy probing through a GPL-3.0 crate, which makes those binaries GPL. Build with --no-default-features to get a binary with no GPL code.

Happy to answer questions about the engine, the book, or ChessBrain.