#chess #tablebase #test-suite #retrograde #endgame

bin+lib retroboard

A chess retrograde move generator, suitable for endgame tablebase generation

15 releases

0.2.10 Apr 16, 2023
0.2.9 Dec 20, 2022
0.2.6 Oct 30, 2022
0.2.4 Aug 19, 2022
0.1.3 Nov 30, 2021

#311 in Game dev

Download history 48/week @ 2024-02-23 60/week @ 2024-03-01

61 downloads per month


1.5K SLoC


crates.io docs.rs

A chess retrograde move generator. Rust port of Retroboard. Suitable for endgame tablebase generation.


Strong test suite but lack of comparaison of perft result against a trusted source.


En-passant is supported, but not castling. Legal but unreachable positions are supported (mainly positions with too many checkers).

Examples of accepted unreachable positions:

  • 8/4k3/3B1B2/8/8/8/8/4K3 b - - 0 1 Impossible check
  • 8/8/R4k2/4p3/8/8/8/4K3 b - e6 0 1 Impossible en passant square. e7e5 would have been illegal because black already in check.

It aims to follow the same generation rules as used by the generation software of syzygy and Gaviota tablebase.


A very rough perft test at depth 4 on this position gives 88148797 moves in ~2s (tested on Apple M1). That is roughly 3.5x times slower than shakmaty crate, but is ought to be improved.

fen : q4N2/1p5k/3P1b2/8/6P1/4Q3/3PB1r1/2KR4 b - - 0 1, with 2PNBRQ in white pocket, 3NBRQP in black one, Q uncastling and allowing en-passant moves.


use retroboard::RetroBoard;

let r = RetroBoard::new_no_pockets("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1").unwrap();
assert_eq!(r.legal_unmoves().len(), 4);


~70K SLoC