Chess Move Validator & Repetition Checker (Flask + Python-Chess)

This project is a Flask web application that validates chess move sequences, detects illegal moves, handles "empty" moves (marked with 'z'), and checks for threefold repetition.

It uses the python-chess library and custom modules for predictions, HTML board rendering, and repetition detection.

🚀 Features

• Enter a sequence of chess moves in SAN (Standard Algebraic Notation).
• Detects illegal moves and reports the move number.
• Handles special "z" marker in move sequences:
  • Stops parsing when "z" is encountered.
  • Reports that an empty move was found.
• Stores user input in Flask session for further processing.
• Checks for threefold repetition using a custom repetition detection function.
• Provides multiple HTML templates for displaying results.

📂 Project Structure

. ├── app.py # Main Flask app ├── minmax.py # model-based move predictor ├── chessBoard.py # HTML chessboard generator ├── repetition.py # Threefold repetition checker ├── templates/ │ ├── index.html # Input form │ ├── legal.html # Shown when all moves are legal │ ├── repetition.html # Repetition results │ └── empty.html # (Optional) predictions page ├── static/ # (Optional) CSS/JS assets └── README.md # Documentation

⚙️ Installation & Setup

1. Clone or download the project files.

2. Install dependencies: pip install flask chess

   (If using prediction features, also install TensorFlow/Keras and NumPy)

3. Run the Flask server: python app.py

4. Open in browser: http://127.0.0.1:5000/

🖥️ Usage

1. Navigate to the index page.
2. Enter a sequence of chess moves (e.g., e4 e5 Nf3 Nc6).
3. The app will:
   • Show "Move sequence is legal" if no errors are found.
   • Report illegal moves with their move number.
   • Report "Empty move found" if a 'z' is present.
4. You can check threefold repetition at /process_repetition, which uses the last entered move sequence stored in the session.

🔬 Key Components

• python-chess: For move validation and FEN board handling.
• Flask session: Stores the last entered move sequence.
• repetition.py: Custom script for detecting threefold repetition.
• Templates:
  • index.html → Input form + error messages.
  • legal.html → Shows legal move sequences.
  • repetition.html → Shows repetition detection results.

🛠️ Future Improvements

• Render the current board state using HTML chessboard.
• Integrate model predictions (minmax.py + CNN model).
• Provide top move suggestions when a "z" marker is found.
• Add user authentication for saving move history.

📜 License

This project is open-source. Feel free to use and modify it for research or educational purposes.