Ruff

Ruff is a Rust-based linter and formatter for Python projects. It suits developers who want lint checks and formatting together across editors and CI; its built-in coverage is broad, but teams that need custom lint rules should choose another approach.

Overview

Ruff brings routine Python code checks and formatting into one tool, with automatic fixes for some violations. Astral describes it as 10–100x faster than existing linters and formatters such as Flake8 and Black, a compelling reason to consider it where turnaround matters, though that is the maker’s claim rather than a guarantee for every project.

Its permissive open-source license and free price make it accessible for individual projects and teams alike. The main trade-off is a fixed rule set: Ruff does not support custom or third-party lint rules.

Compare it with other Linters or Code Formatting Tools.

Key features

Linting, fixes, and security checks

More than 900 built-in rules include native implementations of popular Flake8 plugins, giving Python projects extensive checks without assembling those plugins separately. Ruff can automatically fix lint violations, including removing unused imports. That can reduce routine cleanup, though the availability of fixes does not mean every violation can be resolved automatically.

A Bandit-derived rule group detects common security issues, including possible vulnerabilities in Python code. This adds useful security-oriented checks to the linting workflow, but does not make Ruff a general security testing system.

Formatting and editor workflow

Ruff’s formatter is designed as a drop-in replacement for Black. The intended compatibility makes it a plausible option for Black users seeking a combined tool, but the FAQ notes marginal differences, so projects with strict formatting expectations should account for them.

The built-in Ruff Language Server supplies diagnostics, code actions for fixes, and formatting. The documentation recommends pairing it with another Python language server for navigation and autocompletion; that is an extra component for developers who want those editor capabilities. Setup guides cover VS Code, Sublime Text, PyCharm, and Zed.

Installation and automation

Ruff can be installed through uv, pip, pipx, standalone installers, Homebrew, or Conda. Configuration works through pyproject.toml, ruff.toml, or .ruff.toml, while a published Docker image has both release-specific and latest tags.

Documented CI integrations include GitHub Actions and GitLab CI/CD, and pre-commit hooks provide another route into automated checks. Together, these options let teams fit Ruff into local and CI workflows. Editor setup guidance is offered on a best-effort basis, with issues directed to the project for assistance.

Pricing

Ruff costs free. Its plan is an open-source Python linter and formatter under a permissive license, with autofix, security rules, IDE support, and CI support. There is no paid tier or trial to weigh against a free allowance, and the stated limitation is functional rather than a seat or usage cap: custom rules are not supported.

Platforms

Ruff supports Linux, macOS, Windows, self-hosted use, and web. Installation routes include package managers and standalone installers, and the Docker image supports container-based workflows.

Who it's for

Ruff is a strong fit for Python developers who want substantial built-in lint coverage, automated cleanup, and formatting integrated with editor and CI workflows. It is especially appealing to teams that can use its existing rule set and value a free, permissively licensed tool.

It is a weaker fit for organizations that rely on custom or third-party lint rules. Black users should also allow for marginal formatter differences, while editor users wanting navigation and autocompletion should pair Ruff’s language server with another Python language server.

Pros and cons

• Pros: More than 900 built-in rules, including Flake8-plugin implementations, provide broad Python lint coverage.
• Pros: Automatic fixes, including unused-import removal, can reduce repetitive cleanup.
• Pros: Formatter, editor integrations, CI integrations, and pre-commit hooks support a workflow spanning development and automation.
• Pros: The free, permissively licensed offering has no stated seat or quota caps.
• Cons: Custom and third-party lint rules are unsupported, excluding teams that need organization-specific checks.
• Cons: The formatter can differ from Black at the margins, so exact output compatibility is not assured.
• Cons: Ruff’s editor server does not replace a Python language server for navigation and autocompletion.

Alternatives

Choose Black if you want a free, MIT-licensed Python code formatter rather than Ruff’s combined linting and formatting approach. Choose Prettier for an open-source code formatter with enterprise support and maintenance offered through Tidelift Subscription. Accessibility Test Framework for Android is another free alternative.

goimports is a free open-source command-line tool under the BSD-3-Clause license. rustfmt is a free alternative with no paid plans stated. Zig fmt is free as part of the Zig toolchain. Biome is a free open-source toolchain for web projects. CSharpier offers free, opinionated formatting for C# and XML as a .NET tool.

Verdict

Choose Ruff for a free Python tool that combines extensive built-in lint rules, autofixes, formatting, and practical editor and CI integrations. Look elsewhere if your team must enforce custom or third-party lint rules; that fixed rule set is Ruff’s clearest limit.