What is CheckAI?

CheckAI is a Rust application that provides both a terminal interface and a full-featured REST + WebSocket API for playing chess. It is designed to let AI agents play chess against each other, strictly following the FIDE 2023 Laws of Chess.

Why CheckAI?

Building AI agents that play chess requires a reliable, rule-compliant game server. CheckAI fills that role by providing:

• Correctness — Every move is validated against the complete FIDE 2023 ruleset.
• Programmability — A clean JSON API lets any language or framework drive the game.
• Analysis — A built-in engine evaluates games with 30+ ply search depth, classifying every move from "Best" to "Blunder".
• Flexibility — Use the REST API, WebSocket API, terminal CLI, or embedded Web UI — whichever fits your workflow.

Core Components

Chess Engine

The engine in movegen.rs generates and validates all legal moves, including:

• Standard piece movement (King, Queen, Rook, Bishop, Knight, Pawn)
• Castling (kingside and queenside) with full condition checking
• En passant capture
• Pawn promotion
• Check, checkmate, and stalemate detection
• Draw conditions: 50-move rule, threefold repetition, insufficient material, dead position

REST API

A JSON-based HTTP API powered by Actix Web where agents can:

• Create and manage games
• Query game state and legal moves
• Submit moves and special actions (resign, claim draw)
• Auto-generated Swagger/OpenAPI docs at /swagger-ui/

WebSocket API

A reactive WebSocket endpoint at /ws that mirrors every REST operation and adds:

• Real-time push events for moves, state changes, and game deletions
• Per-game subscriptions
• Archive replay support

Analysis Engine

An asynchronous analysis pipeline that:

• Evaluates completed games at configurable depth (minimum 30 plies)
• Uses PVS/Negascout with transposition tables, null-move pruning, LMR, killer/history heuristics
• Classifies moves as Best / Excellent / Good / Inaccuracy / Mistake / Blunder
• Reports centipawn loss and principal variation per move

Storage

Binary game storage with zstd compression for archiving completed games. Export in text, PGN, and JSON formats.

Tech Stack

Component	Technology
Language	Rust (Edition 2024)
Web Framework	Actix Web 4
WebSocket	Actix Web Actors
Serialization	serde / serde_json
API Docs	utoipa + utoipa-swagger-ui
CLI	clap 4
Compression	zstd
i18n	rust-i18n
Asset Embedding	rust-embed
Containerization	Docker + docker-compose
WASM	wasm-pack + wasm-bindgen
JS Package	@josunlp/checkai (GitHub Packages)