Stylelint

CSS linter that helps developers avoid errors and enforce conventions in stylesheets. It flags invalid syntax, problematic patterns, and unknown properties while supporting rule customization and automatic fixes where possible.

Used by organizations such as Google and GitHub. Compared to basic validators, Stylelint offers over 100 built-in rules, plugin support for custom rules, and shareable configs that teams can extend. It integrates with Prettier so linters and formatters complement each other.

Core capabilities:

• 100+ built-in rules for modern CSS syntax and features
• Plugin system to create custom rules and syntaxes
• Auto-fix for many issues, reducing manual edits
• Shareable and extensible configs
• Parsing for embedded styles in HTML, Markdown, and CSS-in-JS
• Support for SCSS, Sass, Less, and SugarSS

Developers use it to catch malformed grid areas, duplicate selectors, and misspelled property names, and to enforce naming conventions for custom properties, disallow certain units, and limit selector counts. Available as a CLI, Node API, or PostCSS plugin.