Chess Bot

A C# chess engine built with bitboards and accessible via a REST API.

Try it: Chess Bot

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Current Features

Core Engine

• Bitboard Board Representation
• Magic Bitboards
• Legal Move Generation
• *Opening Book
• Repetition Detection
• Multi-threading

Search

• Alpha-Beta Pruning
• Transposition Tables
• Move Ordering
• PVS
• Mate Search
• Asperation Windows
• Null Move Search
• Itterative deeping
• Quiescence Search

Evaluation

• Material Evaluation
• Piece-Square Tables
• Pawn Structure
• NNUE Neural Network - uses Orion 1.1's pretrained network (trained with the Cerebrum library by David Carteau, MIT license)

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Elo Speculation

Based on current implementation, I estimate the bot to play at approximately 2000-2300 Elo. This is an informal estimate.

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Usage

Prerequisites

• .NET 10.0 SDK or later

Building & Running

1. Clone the repository:

   git clone https://github.com/RJDonnison/ChessBot.git
   cd ChessBot

2. Run the API server:

   dotnet run --project ChessBot.Api

   The API will start on http://localhost:5000

Configuration

The engine behavior is controlled via the Engine section in appsettings.json:

{
  "Engine": {
    "Threads": 4,
    "HashMb": 128,
    "TimeMs": 1000,
    "Eval": "Nnue",
    "EvalFile": "Networks/orion64-v1.1.nn"
  }
}

Setting	Description	Default
Threads	Number of search threads (null = auto-detect, clamped 1–8)	null
HashMb	Transposition table size in MB	128
TimeMs	Default think time in milliseconds (per request if no remainingTimeMs provided)	1000
Eval	Evaluation mode: "Nnue" or "Classic" (case-insensitive)	"Nnue"
NnueFile	Path to NNUE network file (relative to API content root or absolute) — only used if Eval=Nnue	(required for Nnue)

When Eval=Nnue, the engine loads the specified network file at startup. If loading fails, it falls back to Classic with a console warning.

Testing with a UI

To test without building a custom UI, you can use the provided Chess Bot Interface.

API Endpoints

GET /bestmove

Returns the best move for a given position.

Parameters:

• fen (required) - The board position in FEN notation
• time (optional) - Remaining time in milliseconds for the player to move (affects think time calculation)

Example:

# Without time (uses default TimeMs setting)
curl "http://localhost:5000/bestmove?fen=rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR%20w%20KQkq%20-%200%201"

# With time (overrides default think time)
curl "http://localhost:5000/bestmove?fen=rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR%20w%20KQkq%20-%200%201&time=30000"

Response:

{
  "bestmove": "e2e4"
}

Integration Example

// Import the ChessBot.Core library
using ChessBot.Core;

var bot = new Bot();
string fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
string bestMove = bot.GetBestMove(fen);
Console.WriteLine($"Best move: {bestMove}");

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Project Structure

• ChessBot.Core - Core engine logic
• ChessBot.Api - ASP.NET API wrapper
• ChessBot.Core.Tests - Unit tests for Perft move generation tests

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Future Features (Roadmap)

• WebAssembly (WASM) - Browser-native engine compilation
• Multi-threading - Parallel search implementation
• ML evaluation - Neural network-based position evaluation (NNUE via Orion 1.1 / Cerebrum)
• History heuristic - Move ordering improvement using historical data
• King safety evaluation - Enhanced king attack detection and safety scoring
• Lazy evaluation - Deferred evaluation for performance

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License

See LICENSE for details.

Third-Party Attribution

This project uses the following third-party assets:

• Orion 1.1 Neural Network (ChessBot.Api/Networks/orion64-v1.1.nn): The pretrained NNUE model from Orion v1.1 by David Carteau. The network file is redistributed unmodified as permitted by its license. For more details, see orionchess.com.

• Cerebrum Library (reference implementation): The NNUE inference code is ported from the Cerebrum library v2.0 by David Carteau, licensed under the MIT License. Copyright © 2025 David Carteau. For the original source, see github.com/david-carteau/cerebrum.