A well tested node.js CSS minifier.
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What is clean-css?

Clean-css is a node.js library for minifying CSS files. It does the same job as YUI Compressor's CSS minifier, but much faster thanks to many speed optimizations and node.js' V8 engine.


What are the requirements?

node 0.6.0+ on UN*X (fully tested on OS X 10.6+ and CentOS)
node 0.8.0+ on Windows

How to install clean-css?

npm install clean-css

How to use clean-css CLI?

Clean-css accepts the following command line arguments (please make sure you use <source-file> as the very last argument to avoid potential issues):

cleancss [options] <source-file>
  • -h, --help output usage information
  • -v, --version output the version number
  • -e, --remove-empty Remove empty declarations (e.g. a{})
  • -b, --keep-line-breaks Keep line breaks
  • --s0 Remove all special comments (i.e. /*! special comment */)
  • --s1 Remove all special comments but the first one
  • -o, --output [output-file] Use [output-file] as output instead of stdout


To minify a public.css file into public-min.css do:

cleancss -o public-min.css public.css

To minify the same public.css into the standard output skip the -o parameter:

cleancss public.css

More likely you would like to concatenate a couple of files. If you are on a Unix-like system:

cat one.css two.css three.css | cleancss -o merged-and-minified.css

On Windows:

type one.css two.css three.css | cleancss -o merged-and-minified.css

Or even gzip the result at once:

cat one.css two.css three.css | cleancss | gzip -9 -c > merged-minified-and-gzipped.css.gz

How to use clean-css programmatically?

var cleanCSS = require('clean-css');
var source = "a{font-weight:bold;}";
var minimized = cleanCSS.process(source);

Process method accepts a hash as a second parameter, i.e., cleanCSS.process(source, options) with the following options available:

  • keepSpecialComments - * for keeping all (default), 1 for keeping first one, 0 for removing all
  • keepBreaks - whether to keep line breaks (default is false)
  • removeEmpty - whether to remove empty elements (default is false)
  • debug - turns on debug mode measuring time spent on cleaning up (run npm run bench to see example)

What are the clean-css' dev commands?

First clone the source, then run:

  • npm run bench for clean-css benchmarks (see test/bench.js for details)
  • npm run check to check JS sources with JSHint
  • npm test for the test suite

How do you preserve a comment block?

Use the /*! notation instead of the standard one /*:

  Important comments included in minified output.


  • Vincent Voyer (@vvo) for a patch with better empty element regex and for inspiring us to do many performance improvements in 0.4 release.
  • Isaac (@facelessuser) for pointing out a flaw in clean-css' stateless mode.
  • Jan Michael Alonzo (@jmalonzo) for a patch removing node's old 'sys' package.
  • @XhmikosR for suggesting new features (option to remove special comments and strip out URLs quotation) and pointing out numerous improvements (JSHint, media queries).


Clean-css is released under the MIT License.