Puffin's CSS Formatter & Validator is a free browser tool for cleaning up and checking stylesheets. Paste CSS, drop a .css file, browse from disk, load a sample, or point at a public URL — then Process to pretty-print and validate.

The checker looks for syntax problems: unclosed braces, strings, comments, and functions, a missing colon or semicolon, an invalid hex color, and a bad rgb() or hsl() count. It reports each problem with its line and column. Warnings cover an unknown property, a duplicate in the same rule, an empty rule, and an @import that comes after other rules. Custom properties and vendor-prefixed properties are left alone.

With Fix CSS enabled, the tool closes what was left open, drops a stray }, inserts a missing colon or semicolon, quotes a bare url(), and moves @charset to the top. A declaration that is not inside a rule is wrapped in :root. Indentation is added between rules. Strings, comments, and custom property names stay as written. Nothing is uploaded to a server — processing runs in your browser (URL fetches are the exception, and may fail when the remote host blocks cross-origin requests).