Ruff turns on 413 lint rules by default, up from 59

Astral's Ruff v0.16.0, released 23 July 2026, enables 413 rules out of the box against the previous 59, so an unconfigured run now catches syntax errors and immediate runtime errors it used to walk past. The release also formats Python inside fenced Markdown code blocks, adds `ruff: ignore` and `ruff: file-ignore` suppression comments alongside the existing disable/enable pairs, prints fix diffs from `check` and `format --check` without a separate `--diff` flag, and stabilises 12 previously preview-only rules.

What it means A sevenfold jump in default rules lights up existing repositories on the first run — which is exactly the kind of large, mechanical, well-specified cleanup a coding agent absorbs better than a human afternoon.