YUI Compressor. According to Yahoo! 's Exceptional Performance Team, 40% to 60% of Yahoo! 's users have an empty cache experience and about 20% of all page views are done with an empty cache (see this article by Tenni Theurer on the YUIBlog for more information on browser cache usage). This fact outlines the importance of keeping web pages as lightweight as possible. Improving the engineering design of a page or a web application usually yields the biggest savings and that should always be a primary strategy. With the right design in place, there are many secondary strategies for improving performance such as minification of the code, HTTP compression, using CSS sprites, etc. In terms of code minification, the most widely used tools to minify JavaScript code are Douglas Crockford's JSMIN, the Dojo compressor and Dean Edwards' Packer.
Each of these tools, however, has drawbacks. Documentation: Detailed description of the YUI Compressor and how to use it. How does the YUI Compressor work? Additional notes. CSS Compressor. Styleneat - CSS Organizer. Online CSS Optimiser / Optimizer. Clean CSS - A Resource for Web Designers - Optmize and Format your CSS.