ruff
Lint and format Python with Ruff. Use when a user asks to set up Python linting, replace flake8/black/isort, configure code quality rules, or speed up Python code formatting.
What this skill does
# Ruff
## Overview
Ruff is an extremely fast Python linter and formatter written in Rust. It replaces flake8, black, isort, pyupgrade, pydocstyle, and dozens more tools — running 10-100x faster. One tool for all Python code quality.
## Instructions
### Step 1: Setup
```bash
pip install ruff
```
### Step 2: Configuration
```toml
# pyproject.toml — Ruff configuration
[tool.ruff]
target-version = "py311"
line-length = 100
src = ["src", "tests"]
[tool.ruff.lint]
select = [
"E", # pycodestyle errors
"W", # pycodestyle warnings
"F", # pyflakes
"I", # isort (import sorting)
"B", # flake8-bugbear
"C4", # flake8-comprehensions
"UP", # pyupgrade
"SIM", # flake8-simplify
"TCH", # flake8-type-checking
"RUF", # ruff-specific rules
]
ignore = [
"E501", # line too long (handled by formatter)
]
fixable = ["ALL"]
[tool.ruff.lint.isort]
known-first-party = ["my_app"]
[tool.ruff.format]
quote-style = "double"
indent-style = "space"
docstring-code-format = true
```
### Step 3: Use
```bash
# Lint
ruff check . # check all files
ruff check . --fix # auto-fix issues
ruff check . --fix --unsafe-fixes # include risky auto-fixes
# Format
ruff format . # format all files
ruff format --check . # check without modifying (CI)
# Watch mode
ruff check --watch .
```
### Step 4: Pre-commit Hook
```yaml
# .pre-commit-config.yaml
repos:
- repo: https://github.com/astral-sh/ruff-pre-commit
rev: v0.3.0
hooks:
- id: ruff
args: [--fix]
- id: ruff-format
```
### Step 5: CI Integration
```yaml
# .github/workflows/lint.yml
- name: Lint with Ruff
run: |
ruff check . --output-format=github
ruff format --check .
```
## Guidelines
- Ruff replaces flake8, black, isort, pyupgrade in a single tool — remove the old ones.
- Start with a broad rule set (`select = ["E", "W", "F", "I", "B", "UP"]`) and expand.
- `ruff check --fix` auto-fixes most issues — safe to run in pre-commit hooks.
- Ruff processes the entire CPython codebase in under 200ms — linting is no longer a bottleneck.
- Use `ruff format` as a drop-in replacement for black — same output, 100x faster.
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