The YUI Compressor is a JavaScript compressor which, in addition to removing comments and white-spaces, obfuscates local variables using the smallest possible variable name.

The YUI Compressor is also able to safely compress CSS files. The decision on which compressor is being used is made on the file extension (js or css).

The YUI Compressor is written in Java and relies on Rhino to tokenize the source JavaScript file. It starts by analyzing the source JavaScript file to understand how it is structured. It then prints out the token stream, omitting as many white space characters as possible, and replacing all local symbols by a letter symbol wherever such a substitution is appropriate . The CSS compression algorithm uses a set of finely tuned regular expressions to compress the source CSS file. The YUI Compressor is open-source.

Several GUI’s are available :

• Smaller (for Mac)
• yuicompressorgui (for Windows)
• Easy YUI Compressor (for Windows)

Online versions are available at the website of Zileex Media, of  Rodolphe Stoclin and of gpbmike.