Ruff Python Linter Dramatically Expands Default Checks in v0.16.0

Astral has released Ruff v0.16.0, a significant update to its Python linting tool, on July 23rd. This new version substantially increases the number of rules enabled by default, jumping from 59 to 413. The total number of rules available in Ruff has also grown from 708 to 968 since the initial default rule set in v0.1.0. Many of these newly enabled rules are designed to catch severe issues, including syntax and immediate runtime errors, which were previously not active by default. This means Ruff can now identify a wider range of problems without requiring explicit user configuration. The update is expected to improve code quality and reduce potential bugs by flagging issues that were previously overlooked. Users can test the latest Ruff on any Python project using the command `uvx ruff@latest check .`. The author tested the new version on their projects Datasette, sqlite-utils, and LLM, finding hundreds of minor issues that violated the new default rules. Despite the extensive test suites for these projects, the enhanced default checks identified previously undetected problems. The command `uvx ruff@latest check . --fix --unsafe-fixes` was used to automatically address many of these issues. For example, on sqlite-utils, this command reported 1618 errors, successfully fixing 1538 while leaving 80 unresolved. Examples of remaining issues include using `datetime.datetime.now()` without a timezone, catching generic `Exception` broadly, and accessing unused attribute values. The author notes that the output from Ruff provides detailed information, making it suitable for use with AI coding agents like Codex and Claude Code for automated code fixes.