I am big fan of Yahoo Developer Network and one of the sections in the site is the “Exceptional Performance” headed until recently by Steve Souders – performance Guru previously at Yahoo and now at Google. Recently Yahoo has come out with a new firefox add-on called YSlow. YSlow is a tool that follows the 13 Rules for High Performance Web Sites as listed on the Yahoo Exception Performance site and analyzes those 13 aspects on your site, giving you a grade (A-F) for each of the rules, and an overall grade for the site. The tool is free to download and installed as an add-on into Firefox firebug plugin.
The 13 benchmarks are listed here
- Make fewer HTTP requests
- Use a CDN
- Add an Expires header
- Gzip components
- Put CSS at the top
- Move scripts to the bottom
- Avoid CSS expressions
- Make JS and CSS external
- Reduce DNS lookups
- Minify JS
- Avoid redirects
- Remove duplicate scripts
- Configure ETags
If you are new to YSlow or the 13 rules for high performance, I strongly recommend reading the links above first before following the article. My mission after reading the articles and installing the plugin was to figure out what does these performance rules mean from a web mapping application perspective.


