Reckless is a UCI chess engine written in Rust as a personal project.

Guided by the insights from the chess programming community, it fearlessly combines established concepts, as the name suggests.

• Bitboards with Little-Endian Rank-File Mapping
• Magic Bitboards for sliding piece attacks
• Copy-Make approach

• Pseudo legal move generator
• Pre-calculated attack maps using Fancy Magic Bitboards
• Magic numbers are pre-generated using Reckless Magics
• Compile time generation of move maps using a build script

• Fail-Soft Alpha-Beta
• Principle Variation Search
• Quiescence Search
• Iterative Deepening
• Aspiration Windows
• Lockless Transposition Table
• Lazy SMP (Shared-Memory Parallel)

• Reverse Futility Pruning
• Null Move Pruning
• Razoring
• Futility Pruning
• Late Move Pruning
• Delta Pruning

• Fractional Late Move Reductions
• Internal Iterative Reductions

• Check Extensions

• Hash Move
• MVV-LVA
• Killer Move Heuristic
• History Heuristic
  • Butterfly History
  • Counter Move History
  • Follow-Up History

• NNUE
• Architecture: (768 -> 128)x2 -> 1
• Activation Function: SCReLU (Squared Clipped Rectified Linear Unit)
• Quantization: i16 (256/64)
• Trained on original data generated entirely through self-play
• Handwritten SIMD for AVX2 instructions

You can download precompiled builds from the GitHub Releases page.

• x86_64-v1: Slowest, compatible with any x86-64 CPU.
• x86_64-v2: Faster, requires support for POPCNT, SEE3, etc.
• x86_64-v3: Even faster, requires support for AVX2, etc.
• x86_64-v4: Fastest, requires support for AVX512.

For detailed information on the specific features needed for each level, refer to the x86-64 microarchitecture levels Wikipedia page.

To build the engine from source, make sure you have Rust 1.65 or a later version installed. If you don't have Rust, follow the official Rust installation guide.

Then, compile the engine using Cargo:

cargo rustc --release -- -C target-cpu=native

Alternatively, you can use the provided Makefile:

# Build for the current CPU architecture
make
# Build release binaries for all microarchitecture levels
make release

Reckless is not a standalone chess program but a chess engine designed for use with UCI-compatible GUIs, such as Cute Chess or ChessBase.

Alternatively, you can communicate with the engine directly using the UCI protocol.

Along with the standard UCI commands, Reckless supports additional commands for testing and debugging:

• OpenBench is the primary testing framework powered by Cute Chess.
• Open source chess engines, like Stockfish, Ethereal, Berserk, and numerous others, for serving as inspiration and providing ideas that fuel development.
• Stockfish Discord server for providing relevant insights and feedback.
• Chess Programming Wiki for contributing to the project's foundation.
• Many thanks to the CCRL team and all chess engine testers for their valuable contributions.

This project is licensed with the MIT license.