stylelint

A mighty, modern linter that helps you avoid errors and enforce conventions in your styles.

Features

It's mighty as it:

understands the latest CSS syntax including custom properties and level 4 selectors
extracts embedded styles from HTML, markdown and CSS-in-JS object & template literals
parses CSS-like syntaxes like SCSS, Sass, Less and SugarSS
has over 170 built-in rules to catch errors, apply limits and enforce stylistic conventions
supports plugins so you can create your own rules or make use of plugins written by the community
automatically fixes the majority of stylistic violations
is well tested with over 15000 unit tests
supports shareable configs that you can extend or create
is unopinionated so that you can customize it to your exact needs
has a growing community and is used by Facebook, GitHub and WordPress