Two of the five testimonials in the README mention intentionally introducing errors to be sure ruff was even running. I admit I did the same when I first tried ruff. It's cool that ruff is so fast people aren't sure it ran at all, but perhaps it is also a UX problem?

When black finds nothing to complain about, it says:

All done! ✨ 🍰 ✨
<n> files left unchanged.

pylint:

Your code has been rated at 10.00/10

mypy:

Success: no issues found in <n> source files

Perhaps ruff could do something similar if no errors are found? For example:

$ ruff check .
Found 0 errors in <n> files 🎉

On the other hand, several linters are silent if they find nothing (pycodestyle, flake8, isort, etc.).