esca

A chess model that answers what is true about a position — a Rust crate and a Python package built from it.

The esca is the anglerfish's lure: the small thing that lights up what is in front of it.

Position is placement and state and nothing else. Rules live in Variant implementations — Classic and Chess960 — so a position can be asked the same question under different rules, and a new variant is a new implementation and nothing else. A Game pairs a variant with the moves played, which is what repetition and claimable draws need. Facts answers what is true about a position, both as prose a reader can check and as the flat f32 row a net consumes.

Rust

[dependencies]
esca = "0.1"

use esca::{Game, Schema, Side, classic};

let mut game = Game::new(classic());   // Chess960 rules: `esca::chess960()`
game.play_san("e4").unwrap();
game.play_uci("e7e5").unwrap();
println!("{}", game.position().fen());

let facts = game.facts();              // side-relative, in the mover's view
println!("{}", facts.tactics[Side::Us.index()].legal_move_count);
println!("{}", facts.summary());

let schema = Schema::v0();             // the row a net eats: 1065 f32
println!("{}", facts.encode(schema, schema.all()).len());

Cargo features, neither on by default: lichess (streaming reader for the Lichess evaluation dump) and python (the PyO3 module the wheel is built from).

Python

pip install esca

import esca

game = esca.Game()  # Chess960 rules: esca.Game(variant=esca.CHESS960)
game.play_san("e4")
game.play("e7e5")
print(game.position.fen)

facts = game.facts()  # side-relative: index with esca.US / esca.THEM
print(facts.tactics[esca.US].legal_move_count)
print(facts.summary())

rows = esca.encode([game.position.fen])  # (1, 1065) float32, ready for a net
print(rows.shape, esca.SCHEMA_ID)

Wheels are abi3 for Python 3.12 and up. esca.lichess.batches() streams the evaluation dump as encoded batches with their targets.

What it covers

  • Classic chess and Chess960, behind one Variant trait.
  • FEN and EPD, reading KQkq and the AHah of X-FEN and Shredder-FEN alike, and writing KQkq whenever the rook files allow it.
  • Legal move generation into a MoveList that never allocates.
  • UCI move text in either castling spelling, and SAN with the disambiguation it needs.
  • Checkmate, stalemate, insufficient material, the fifty- and seventy-five-move rules, and threefold and fivefold repetition.
  • Facts: nine groups of cheap position facts — state, material, pawns, pieces, king, mobility, attacks, one-ply tactics and attack planes — plus MoveFacts for every legal move, all side-relative and in the mover's view.
  • Schema, a versioned manifest with a schema_id, and batch encoders that write f32 rows without allocating.

Documentation

License

MIT — see LICENSE.

Project links

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  • Released:
Newer release available (0.3.0)

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Avatar for amyodov from gravatar.com amyodov

Credits

Author: Alexander Myodov

GitHub Statistics

Data verified by PyPI on Sep 3, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License

MIT License (MIT)

Requires

Python >=3.12

Tags

chess chess960 fen san position

Classifiers

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