Pewter is a hobby chess engine written from scratch in the Rust programming language. It is not a complete chess program — it speaks the UCI protocol over stdin/stdout and is meant to be driven by a chess GUI or by another program, rather than used directly.

The project is a Cargo workspace:

Pewter targets a recent stable Rust toolchain and uses the 2024 edition, so it needs Rust 1.85 or newer. Install Rust via rustup if you don't already have it.

# Debug build of everything
cargo build --workspace

# Optimised build (use this for actually playing — it is dramatically stronger
# per unit time than the debug build)
cargo build --release

The release engine binary is written to target/release/pewter-engine.

# Run the test suite
cargo test --workspace

# Formatting, lints and micro-benchmarks
cargo fmt --all --check
cargo clippy --workspace --all-targets -- -D warnings
cargo bench -p pewter-core

These are the same checks the CI workflow runs on every push and pull request.

pewter-engine is a UCI engine: it reads UCI commands on stdin and writes responses on stdout. You can talk to it by hand to sanity-check it:

$ cargo run --release --bin pewter-engine
uci
# ... engine identifies itself and lists its options, ending with `uciok`
position startpos moves e2e4 e7e5
go depth 8
# ... engine searches and replies with `bestmove ...`
quit

Supported UCI options include Hash (transposition table size in MiB) and the Wobble / WobblePlies pair used to add controlled randomness to the opening (handy for generating varied self-play games).

Any UCI-compatible GUI can drive Pewter. Build a release binary and register target/release/pewter-engine as a new UCI engine in your GUI of choice, for example:

• Cute Chess
• Arena
• Banksia GUI
• En Croissant

The GUI handles the board, clocks and opponent; Pewter just needs the path to the binary.

The tourney/ directory contains a Python harness for A/B-testing engine changes: it plays two UCI engines against each other over many games and reports the score, Elo difference and likelihood of superiority. See tourney/README.md for details.

• crates/ — the Rust workspace (see the table above).
• tourney/ — Python tournament harness for comparing engine builds.
• docs/ — design notes, including the engine-strength roadmap.

Pewter is distributed under the terms of the MIT license.