Ruff

Ruff does the work of flake8, black, isort, pylint, and pyupgrade in one pass, fast enough that linting stops being a step you wait on. It is a Python linter and formatter written in Rust, MIT licensed, no paid tier, no account. Version 0.16 flipped the default rule set from 59 rules to 413.

Nothing to host: one binary, one config block in pyproject.toml, one CI step. The upgrade is where the work is, because 413 default rules pointed at a mature codebase produces a wall of new findings to triage.

Solo and small teams should install it and delete the other five tools. Medium teams should budget an afternoon for the migration. Large teams should pin the version so a patch bump does not change what fails in CI. In JavaScript, biomejs/biome and oxc-project/oxc do the same job, and astral-sh/uv comes from the same team.

The catch: Ruff still has no custom plugin system, so team-specific flake8 plugins have nowhere to go. Astral was acquired by OpenAI in March 2026 and its paid registry pyx stopped taking signups. MIT means a fork stays possible, but the roadmap now belongs to a company whose main business is not Python tooling.