Ruff

Extremely fast Python linter and formatter written in Rust by Astral. Current version is 0.15.7. Two separate subcommands: ruff check (linting, replaces Flake8/isort/pyupgrade) and ruff format (formatting, replaces Black). Not a Python library to import — CLI tool only. The format setting and RUFF_FORMAT env var were repurposed/removed; use output-format and RUFF_OUTPUT_FORMAT instead. 2026 style guide introduced in 0.15.0 changes lambda formatting.