What's this about?
Ruff, the extremely fast Python linter from Astral, turned on 413 rules by default in version 0.16, up from 59. Simon Willison ran it across his projects and got 1618 findings in sqlite-utils alone; his writeup is a practical tour of triaging the flood — which new defaults catch real bugs and which are noise.
What exactly is a "linter"?
A linter is a program that reads your code without running it and flags likely problems — unused variables, risky patterns, style violations — like spell-check for source code. "Default rules" are the checks that run out of the box; multiplying them by seven overnight means every codebase suddenly looks much dirtier than it did last week.
Why does it matter?
In the agent era linters have quietly become guardrails for AI-written code — the cheap, mechanical review layer everyone (including Uncle Bob's "don't read the code" pipeline) leans on. What a major linter enables by default effectively becomes the floor of code quality for agents.