About the CSS Minifier
This minifier runs csso in your browser. Beyond stripping whitespace and comments, it shortens colour values (#ffffff to #fff, rgb(0,0,0) to #000), removes redundant units from zeros, collapses margin: 1px 1px 1px 1px to margin: 1px, and with restructuring on, merges rules with identical selectors or declarations. The result applies exactly the same styles with fewer bytes; typical savings are 20 to 40 percent before gzip.
Restructuring reorders rules where that is provably safe. If you rely on source order for a specificity tie or use hacks that depend on duplicates, untick it and the minifier will only remove whitespace and shorten values. Comments starting with /*! can be kept for licence headers.
The stylesheet is syntax-checked first, so a missing brace stops the process with a line number rather than producing broken output. Use the CSS Formatter to expand a minified file again.
How to use
- Paste CSS or upload the file.
- Leave restructuring on unless you depend on rule order for overrides.
- Copy or download the minified stylesheet; the stats line shows the byte saving.
Common questions
- Can minification break my styles?
- Whitespace removal and value shortening cannot. Restructuring is designed to be safe, but if you use unusual override patterns, turn it off and compare.
- Does it add vendor prefixes or remove unused CSS?
- No. It only compresses what you give it. Autoprefixing and purging are build-time steps.
- How does it compare to cssnano?
- csso is comparable in output size for most stylesheets and runs without a build step. The differences are in edge-case optimisations.
- Are @media queries merged?
- Identical media queries are merged when restructuring is on.