ruff

library0.16.4pypypi✓ verified 27d ago

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.

testing

uv tool install ruff@latest

github ↗package ↗homepage ↗docs ↗changelog ↗

INSTALL

IMPORT

SIG · RUFF

ruff

testingpythonv0.16.4

Install

2.5s avg

Import

—

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v0.16.4 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.000s · 18.2MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 2.5s · import 0.000s · 19MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

ruff (CLI)

✓ # ruff is a CLI tool — not a Python library to import # Two separate subcommands: # Linting (replaces flake8, isort, pyupgrade, etc.) ruff check . # lint all files ruff check . --fix # lint and auto-fix safe issues ruff check . --unsafe-fixes # also apply unsafe fixes # Formatting (replaces Black) ruff format . # format all files ruff format . --check # check only, no changes # Configuration in pyproject.toml: # [tool.ruff] # line-length = 88 # [tool.ruff.lint] # select = ["E", "F", "B", "I"] # [tool.ruff.format] # quote-style = "double"

✗ import ruff # ModuleNotFoundError — ruff is a CLI tool from ruff import check # ModuleNotFoundError

ruff is a CLI tool only. Configure via pyproject.toml [tool.ruff] or ruff.toml. Two subcommands: ruff check for linting, ruff format for formatting.

ruff check for linting, ruff format for formatting. Configure in pyproject.toml [tool.ruff].

# Install pip install ruff # Lint all Python files in current directory ruff check . # Lint with auto-fix ruff check . --fix # Format all Python files ruff format . # Check formatting without modifying (for CI) ruff format . --check # Minimal pyproject.toml config # [tool.ruff] # line-length = 88 # target-version = "py311" # # [tool.ruff.lint] # select = ["E", "F", "B", "I", "UP"] # ignore = ["E501"] # # [tool.ruff.format] # quote-style = "double" # indent-style = "space" # Pre-commit hook (pin the version!) # - repo: https://github.com/astral-sh/ruff-pre-commit # rev: v0.15.7 # hooks: # - id: ruff-check # args: [--fix] # - id: ruff-format

ruff --version

Debug

Known issues

breakingThe format setting in [tool.ruff] was repurposed: it no longer controls CLI output format. Use output-format instead. The RUFF_FORMAT env var was removed — use RUFF_OUTPUT_FORMAT. Old configs using format = 'json' to get JSON output are silently broken.

fix

Replace [tool.ruff] format = 'json' with [tool.ruff] output-format = 'json'. Replace RUFF_FORMAT=json with RUFF_OUTPUT_FORMAT=json.

affects: >= 0.2.0

breaking2026 style guide (introduced in 0.15.0) changes lambda formatting — lambda bodies are now parenthesized instead of breaking parameters across lines. Reformatting existing code will produce diffs.

fix

Run ruff format . after upgrading to reformat under the 2026 style guide. Review diffs carefully, especially for lambdas as function arguments.

affects: >= 0.15.0

breakingbuild/ directory no longer excluded by default. Previously ruff excluded build/, which caused confusion when projects had a legitimate build/ directory. Now build/ is only excluded if in .gitignore or extend-exclude.

fix

If you relied on build/ being excluded, add it explicitly: [tool.ruff] extend-exclude = ['build']

affects: >= 0.4.0

gotcharuff check and ruff format are separate subcommands — running ruff check does NOT format code. Need both: ruff check --fix && ruff format. In pre-commit, two separate hooks are needed: ruff-check and ruff-format.

fix

Use both subcommands. In pre-commit: - id: ruff-check then - id: ruff-format. ruff-check must come BEFORE ruff-format when using --fix.

affects: all

gotchaRuff only enables F (Pyflakes) and a subset of E (pycodestyle) rules by default. Common rules like isort (I), bugbear (B), pyupgrade (UP) must be explicitly selected. Not specifying select means most linting power is unused.

fix

Add to [tool.ruff.lint]: select = ['E', 'F', 'B', 'I', 'UP', 'RUF']. Or use select = ['ALL'] with specific ignores.

affects: all

gotcha--format flag on ruff check and ruff linter was renamed to --output-format. Using --format raises an error.

fix

Replace ruff check --format json with ruff check --output-format json.

affects: >= 0.2.0

gotchaThe command 'pip install ruff' was executed as Python code, leading to a SyntaxError. Pip commands should be run directly in the shell or via a subprocess call, not as part of a Python script.

fix

Execute `pip install ruff` directly in your shell environment or, if running from a Python script, use `subprocess.run(['pip', 'install', 'ruff'], check=True)`.

affects: all

gotchaRunning shell commands (like `pip install`) directly within a Python script will raise a `SyntaxError: invalid syntax`. Python interprets such lines as invalid Python code rather than shell commands.

fix

To execute shell commands like `pip install ruff` from within a Python script, use `import subprocess; subprocess.run(['pip', 'install', 'ruff'])` or `import os; os.system('pip install ruff')`.

affects: all

Upgrade

Version history

0.16.4latest on PyPI · released Aug 20, 2026

Audit

Dependencies

No dependency data recorded yet.

Agent activity

11 hits · last 30 days

node

Resources

githubhttps://github.com/astral-sh/ruff ↗

packagehttps://pypi.org/project/ruff/ ↗

homepagehttps://docs.astral.sh/ruff ↗

docshttps://docs.astral.sh/ruff/ ↗

changeloghttps://github.com/astral-sh/ruff/blob/main/CHANGELOG.md ↗