Ruff
Extremely fast Python linter and formatter, written in Rust
The Lens
Ruff replaces Pylint, isort, and black with a single pass that runs 10-100x faster. It's a Python linter and formatter written in Rust that replaces five or six tools at once. The speed difference is not subtle. Large codebases that took 30 seconds now take under a second.
Everything is free under MIT. No paid tier, no cloud, no account. Ruff is from Astral (same team as uv), and like uv, there's no monetization yet. Every rule from flake8, isort, pycodestyle, pyflakes, and more is reimplemented and included.
The catch: Ruff doesn't support custom plugins the way flake8 does. If your team relies on custom flake8 plugins for domain-specific rules, you can't migrate those yet. And like uv, Astral's long-term business model is undefined. You're betting on a VC-funded company's goodwill. The Apache/MIT license protects you, but active maintenance isn't guaranteed forever.
Free vs Self-Hosted vs Paid
fully freeFully open source under MIT. Replaces flake8, pylint, isort, black, pycodestyle, and others, all of which are also free. The value isn't cost savings but developer experience and CI speed.
**CI impact:** A Python monorepo that takes 45 seconds to lint with flake8 + black + isort takes 0.5 seconds with Ruff. For teams running CI on every push, that's meaningful time savings at $0 incremental cost.
**Astral's funding:** $32M Series A. No announced revenue model. The tool is MIT-licensed, so even if Astral pivots, the community can maintain it.
Free. No paid tier exists. MIT licensed.
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