Stylelint

I co-created Stylelint, an open-source CSS linter that flags problematic code using more than 170 built-in rules. It extracts embedded styles from HTML, Markdown and CSS-in-JS, as well as parsing CSS-like syntaxes like SCSS.
We built it for Node.js using PostCSS. It has over fifteen thousand unit tests using Jest and extensive documentation.
It’s downloaded ten million times a month and companies worldwide use it, including GitHub and Google.