I’ve recently found a fantastic new add on for Firefox. It is based on the work that Yahoo’s Steve Souders has done to help speed up websites at the most significant point: the front end. He argues in his video that the front end is the main area where significant speed gains can be made. The help page for the add give a good details on the performance rules the YSlow uses, but in summary, the 14 best practices are:

1. Make Fewer HTTP Requests
2. Use a Content Delivery Network
3. Add an Expires Header
4. Gzip Components
5. Put Stylesheets at the Top
6. Put Scripts at the Bottom
7. Avoid CSS Expressions
8. Make JavaScript and CSS External
9. Reduce DNS Lookups
10. Minify JavaScript
11. Avoid Redirects
12. Remove Duplicate Scripts
13. Configure ETags
14. Make Ajax Cacheable

I’m more comfortable with some of these than others, and some are not practical, or even affordable for smaller sites, but you get the general idea.

The YSlow plug in requires Firefox, and that the FireBug add on to be installed first (which is itself an essential add on for web developer).