CSS Minifier
FormattersMinify CSS with csso. Removes comments, merges duplicate selectors, shortens colour values, and collapses redundant rules. Shows compression ratio. Browser-based.
About CSS Minifier
The CSS Minifier compresses CSS stylesheets using csso — the most structurally-aware CSS minifier available. Unlike whitespace-only strippers, csso performs genuine optimisations: it merges duplicate selectors and rule declarations, shortens `#rrggbb` colour values to `#rgb` where possible, removes redundant property overrides, and collapses compatible shorthand properties. The result is the smallest structurally valid CSS output. Compression ratio and exact byte savings are shown after each run. A download button saves the minified output directly. All processing runs in a Web Worker; your stylesheets never leave the browser.
Features
- ✓Powered by csso — a structural CSS optimiser, not just a whitespace stripper
- ✓Merges duplicate selectors and redundant rule blocks
- ✓Shortens hexadecimal colour values (#rrggbb → #rgb where applicable)
- ✓Removes redundant property overrides and collapses compatible shorthands
- ✓Strips all CSS comments (block and inline)
- ✓Collapses multi-value shorthand properties (margin, padding, border)
- ✓Displays compression ratio and exact byte savings after minification
- ✓Download minified output as a .css file with one click
- ✓Language picker — instantly switch to SCSS, Less, JavaScript, or other minifiers
- ✓One-click clipboard copy of minified output
- ✓Web Worker execution — minification never blocks the UI
- ✓Mobile-responsive layout with a dedicated Minify button
- ✓100% client-side — your stylesheets never leave the browser
Common Use Cases
- Minifying production CSS bundles before deploying to CDN or servers
- Compressing component stylesheets for inline embedding in HTML
- Reducing stylesheet size for performance-critical pages and Core Web Vitals
- Quickly comparing CSS file size before and after adding styles
- Minifying CSS output from SCSS or Less compilers before shipping
- Stripping all comments from CSS before open-sourcing a stylesheet
Frequently Asked Questions
QWhat is the difference between csso and a simple whitespace stripper?
A whitespace stripper removes spaces and newlines. csso performs structural optimisation — merging identical selectors, collapsing shorthand properties, removing overridden declarations, and shortening colour values — producing significantly smaller output.
QDoes csso support CSS custom properties (variables)?
Yes — csso treats custom properties as opaque values and preserves them correctly. It does not attempt to evaluate or inline CSS variable values.
QIs my CSS sent to a server?
No. csso runs in a Web Worker entirely inside your browser. Nothing is transmitted to any server.
QWhat is the difference between the CSS Minifier and SCSS Minifier?
The CSS Minifier uses csso for deep structural optimisation on compiled CSS. The SCSS Minifier performs source-level minification — stripping comments and collapsing whitespace from SCSS source without compiling it first.