Ruff vs Qlty (formerly Code Climate Quality)
Feature checklists rarely decide anything. What decides it is the pricing metric, who has to write the tests, and which limitation you can live with.
Entry price
Free and open source
Open sourceFrom $20 per contributor/month (Pro; Enterprise $30)
Free tierWhat drives the bill
The metric that actually scales your invoice.
Free and open source. You pay in engineering time and CI minutes.
Priced per contributor. Free for K-12 and universities, 10% off for registered non-profits.
Free tier
Everything, self-hosted
Free plan with unlimited contributors, 1,000 analysis minutes and 100 AI autofixes a month.
Open source
MIT
Self-hostable
No-code authoring
Languages
Platforms
Fits teams
Adoption
Category standard
Astral · since 2022
Established
Qlty Software (spun out of Code Climate) · since 2011
Strengths
- Replaces Flake8, isort, Black, pyupgrade and more with a single fast binary.
- Fast enough to run on every keystroke in the editor.
- Straightforward migration from existing Flake8 configurations.
- Maintainability grading is easy to communicate to non-engineers.
- Coverage and quality tracked together in one PR check.
- Free for open source.
Limitations
- Not every niche Flake8 plugin rule has been ported.
- Type checking is a separate concern — you still need mypy or ty.
- Rapid release cadence occasionally changes behaviour.
- Letter grades oversimplify and can drive the wrong behaviour.
- The Code Climate to Qlty transition means older documentation, URLs and integration guides still say Code Climate.
- Velocity, the companion engineering-metrics product, was sunset — do not buy expecting it.
Best for
Every Python project.
Teams that want a simple maintainability signal in pull requests.
Pricing last reviewed August 2026 and is indicative only — confirm on each vendor’s own page.