Nu developer documentation

Nu is a maintained, modernized continuation of the Mu editor — a simple Python code editor for beginner programmers.

Note

This documentation is for developers who want to work on Nu itself, not for end users (who want Using Nu). Much of it is inherited from upstream Mu and still describes the pre-fork toolchain (PyQt5, setup.py, Sphinx/ReadTheDocs, and the micro:bit/web modes). Nu has since moved to PyQt6, Python 3.11+, uv and ruff, and trimmed the mode set to Python 3, Pygame Zero, CircuitPython and the debugger. For the current, authoritative state of the project see README.md, CLAUDE.md and TODO.md in the repository root. These pages are being modernized incrementally.

Where to start

• New here? Read the developer setup and the first steps for new contributors.
• Want the big picture? Start with the architecture overview.
• Writing a mode? Follow the modes tutorial.
• Curious how the debugger works? See debugger / runner.
• Adding tests or translations? See tests and translations.

How the docs are built

These docs are written in Markdown and built with MkDocs using the Material theme. The API reference is generated from the source docstrings with mkdocstrings. Build locally with make docs (or live-preview with make docs-serve).