# Stockfish — The Strongest Open Source Chess Engine

> A free UCI chess engine consistently ranked number one in computer chess ratings, using advanced search algorithms and an efficiently updatable neural network for evaluation.

## Install

Save in your project root:

# Stockfish — The Strongest Open Source Chess Engine

## Quick Use
```bash
# Download binary from https://stockfishchess.org/download/
./stockfish
# In UCI mode:
uci
position startpos moves e2e4 e7e5
go depth 20
```

## Introduction
Stockfish is the strongest open-source chess engine in the world, consistently topping computer chess rating lists. It combines a highly optimized alpha-beta search with NNUE (Efficiently Updatable Neural Network) evaluation, achieving superhuman playing strength on standard hardware.

## What Stockfish Does
- Plays chess at superhuman strength using the Universal Chess Interface (UCI) protocol
- Analyzes positions with multi-PV support for exploring alternative lines
- Evaluates positions using a neural network trained on billions of self-play games
- Supports multi-threaded search to scale with available CPU cores
- Provides endgame tablebase probing for perfect play in simplified positions

## Architecture Overview
Stockfish uses iterative deepening with alpha-beta pruning enhanced by null-move pruning, late move reductions, and futility pruning. The NNUE evaluation network runs entirely on the CPU using SIMD instructions, updating incrementally as pieces move. The search is parallelized using a shared hash table (Lazy SMP) where threads explore different parts of the search tree simultaneously. Transposition tables, killer moves, and history heuristics guide move ordering.

## Self-Hosting & Configuration
- Compile from source with `make -j profile-build ARCH=x86-64-avx2` for optimal performance
- Pre-built binaries are available for all major platforms
- Configure via UCI options: Hash size, Threads count, and SyzygyPath for tablebases
- Integrates with any UCI-compatible GUI (Arena, CuteChess, en-croissant)
- Neural network file (nn-*.nnue) is embedded in the binary at compile time

## Key Features
- NNUE evaluation provides deep positional understanding without GPU requirements
- Efficient Lazy SMP parallelism scales nearly linearly up to 8-16 threads
- Syzygy tablebase support for perfect endgame play with up to 7 pieces
- Extremely low resource usage compared to GPU-based engines
- Open development with automated testing infrastructure (Fishtest)

## Comparison with Similar Tools
- **Leela Chess Zero (Lc0)** — GPU-based MCTS engine; Stockfish is CPU-based and generally stronger
- **Komodo** — commercial engine; Stockfish is free and typically higher rated
- **GNU Chess** — much weaker; Stockfish is 1000+ Elo points stronger
- **AlphaZero** — DeepMind research project, not publicly available; Stockfish is open source

## FAQ
**Q: How strong is Stockfish?**
A: Estimated 3600+ Elo on CCRL rating lists, far beyond any human player.

**Q: Does Stockfish need a GPU?**
A: No. NNUE runs entirely on CPU using SIMD instructions. A modern multi-core CPU is sufficient.

**Q: Can I use Stockfish in my application?**
A: Yes, under the GPLv3 license. Any derivative work must also be open source.

**Q: How is the neural network trained?**
A: Through billions of self-play games analyzed with Stockfish itself, continuously improved by the community.

## Sources
- https://github.com/official-stockfish/Stockfish
- https://stockfishchess.org/

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Source: https://tokrepo.com/en/workflows/asset-758ac620
Author: AI Open Source