Yahoo! released an excellent performance utility on YDN called YSlow, to help you understand why your pages are slow. YSlow is a Firebug addon. It provides different views to analyze your pages :
- Performance View: YSlow analyzes any web page and generates a grade for each rule and an overall grade. If a page can be improved, YSlow lists the specific changes to be made.
- Stats View: YSlow calculates the total size of the web page for both empty cache and primed cache scenarios, as well as information about cookies.
- Components View : YSlow lists all the components in the page including their type, URL, Expires date, gzip status, load time, size, and ETag. You can also view the HTTP response headers for any component.
Yahoo!’s Exceptional Performance team have a great reference with best practices for improving web performance, including rules and research papers. Be sure to check it out.