My blog post: Building My Own Chess Engine

A chess engine which implements:

• Alpha-beta pruning for move searching
• Move ordering based off heuristics like captures and promotions
• Tomasz Michniewski's Simplified Evaluation Function for board evaluation and piece-square tables
• A slice of the Universal Chess Interface (UCI) to allow challenges via lichess.org
• A command-line user interface

It uses Python 3.8 with type hints as well as unit + integration tests. Mypy checks type hints as part of the GitHub Actions CI pipeline.

pip install -r requirements.txt

Start the engine with:

python ui.py

Start as [w]hite or [b]lack:
w

  8 ♖ ♘ ♗ ♕ ♔ ♗ ♘ ♖
  7 ♙ ♙ ♙ ♙ ♙ ♙ ♙ ♙
  6 · · · · · · · ·
  5 · · · · · · · ·
  4 · · · · · · · ·
  3 · · · · · · · ·
  2 ♟ ♟ ♟ ♟ ♟ ♟ ♟ ♟
  1 ♜ ♞ ♝ ♛ ♚ ♝ ♞ ♜
    a b c d e f g h

Enter a move like g1h3:

Start the engine with:

python main.py

An example interaction with the engine (responses have #):

uci
# id name Andoma
# id author Andrew Healey & Roma Parramore
# uciok
position startpos moves e2e4
go
# bestmove g8f6

Also accepts a FEN string:

position fen rnbqk1nr/p1ppppbp/1p4p1/8/2P5/2Q5/PP1PPPPP/RNB1KBNR b KQkq - 0 1

See the UCI interface doc for more information on communicating with the engine.

Debug information (the number of positions searched, the time taken) is sent to stderr. The engine's response is sent to stdout.

The UCI protocol slice that's implemented by this engine means you can play it via lichess.org by using ShailChoksi/lichess-bot (a bridge between Lichess API and chess engines) and a BOT account.

The engine file required by lichess-bot may be generated using pyinstaller.

There are unit tests for the engine, UI, and evaluation modules. Mate-in-two/mate-in-three puzzles are being added.

python -m unittest discover test/

Type hints:

pip install -r requirements-dev.txt

mypy .