ruff

ruff

Ruff is an extremely fast Python linter and code formatter. It replaces Flake8, isort, Black, pyupgrade, autoflake, and dozens of other tools.

When to use ruff

Always use ruff for Python linting and formatting, especially if you see:

• [tool.ruff] section in pyproject.toml
• A ruff.toml or .ruff.toml configuration file

However, avoid making unnecessary changes:

• Don't format unformatted code - If ruff format --diff shows changes throughout an entire file, the project likely isn't using ruff for formatting. Skip formatting to avoid obscuring actual changes.
• Scope fixes to code being edited - Use ruff check --diff to see fixes relevant to the code you're changing. Only apply fixes to files you're modifying unless the user explicitly asks for broader fixes.

How to invoke ruff

• uv run ruff ... - Use when ruff is in the project's dependencies to ensure you use the pinned version
• uvx ruff ... - Use when ruff is not a project dependency, or for quick one-off checks
• ruff ... - Use if ruff is installed globally

Commands

Linting

ruff check .                  # Check all files in current directory
ruff check path/to/file.py    # Check specific file
ruff check --fix .            # Auto-fix fixable violations
ruff check --fix --unsafe-fixes .  # Include unsafe fixes (review changes!)
ruff check --watch .          # Watch for changes and re-lint
ruff check --select E,F .     # Only check specific rules
ruff check --ignore E501 .    # Ignore specific rules
ruff rule E501                # Explain a specific rule
ruff linter                   # List available linters

Formatting

ruff format .                 # Format all files
ruff format path/to/file.py   # Format specific file
ruff format --check .         # Check if files are formatted (no changes)
ruff format --diff .          # Show formatting diff without applying

Configuration

Ruff is configured in pyproject.toml or ruff.toml: