pawnocchio

Strongest UCI chess engine written in zig

Version	Release Date	CCRL 40/15	CCRL Blitz	CEGT 40/20	ipman r9 list	Chess324 Top15
1.8	2025-07-22	3564 (#20)	3697 (#16)	3544 (#18)	3517	3680 (#12)
1.7	2025-05-31	3528	3642	3491	3448
1.6.1	2025-05-15	3500*	3622	3440*
1.6	2025-04-27	3490	3600*	3433
1.5	2025-04-18	3450*	3500	3350
1.4.1	2025-04-05	3425	3450*
1.3.1415	2025-03-14	3365	3401
1.3	2025-03-07	3201
1.2	2025-02-21	3120
1.1	2025-01-24	2432
1.0	2025-01-20	2100*

*estimated

Features

Supports FRC, also known as Chess960

Search

The search is a standard alpha-beta search with the following enhancements:

• Iterative deepening
• Quiescence search
• Aspiration windows
• Principal variation search
• Transposition table
  • Move ordering
  • Cutoffs
  • Static evaluation correction
• MVV and SEE ordering of captures
• History Heuristic (standard history, 1 ply conthist, and noisy history)
• Reverse futility pruning
• Null move pruning
• Razoring
• Mate distance pruning
• History pruning
• Singular extensions
  • Double extension
  • Multicut
  • Negative extensions
• Correction history

Evaluation

The evaluation is done using a neural net trained entirely on self play games from zero knowledge using the excellent open source bullet neural network trainer. The architecture of the network is (768x8hm -> 1280)x2 -> 1x8

Build instructions

1. Get the network with git submodule update --init --depth 1
2. Install zig (0.14.0)
3. zig build --release=fast --prefix <installation path> (for example --prefix ~/.local will put pawnocchio in ~/.local/bin/pawnocchio) The Makefile is only intended to be used for testing on Openbench.

Licensing

• The code is licensed under the GPLv3 license. Full text can be found in LICENSE in the project root
• The assets are licensed under the CC-BY-ND 4.0 license. Full text can be found in assets/LICENSE

Credit

• Pyrrhic by Andrew Grant for tablebase probing, under the MIT license.
• Jackal by snekkers for inspiration styling this readme