Sunfish
Sunfish: a Python Chess Engine in 111 lines of code
...Despite being only around a hundred lines of core logic, the engine achieves competitive performance, reaching ratings above 2000 on online platforms. It implements classic chess engine techniques such as alpha-beta pruning and efficient board representation while maintaining readability and simplicity. The project is often used as an educational tool for understanding game AI, search algorithms, and evaluation functions without the complexity of larger engines. It includes a simple UCI-compatible interface, allowing it to be integrated with graphical chess interfaces or used in terminal-based gameplay. ...