Pre-Commit Demo

This repo is a companion piece to the blog post Why Pre-Commit Hooks Are Essential (Even If You Hate Them At First) on bearblog.

What's this project about?

A minimal Python project that demonstrates pre-commit hooks, including a custom hook that uses an LLM to review your changes.

Setup

This project uses uv for dependency management.

# Sync dependencies
uv sync

# Install pre-commit hooks (anthropic library will be auto-installed by pre-commit)
uv run pre-commit install

Custom hook: llm-check

A custom pre-commit hook that calls an LLM to look at your staged changes and give a pass/fail score. Lives in hooks/llm_check.py.

Set your API key to enable it:

export ANTHROPIC_API_KEY="your-key-here"

If the key is not set the hook will skip gracefully.

Config highlights

The .pre-commit-config.yaml demonstrates several useful patterns:

• exclude on end-of-file-fixer - the fixed-width data file in data/ must not have a trailing newline added
• args on mixed-line-ending - passes --fix=lf to enforce Unix-style line endings
• repo: local - defines the llm-check hook as a local script rather than pulling from a remote repo