I would like to write some words concerning YSlow. It’s a tool which analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
Originally, it was an add-on developped by Yahoo! for the Firebug extension in Firefox. It is also widely used by webmasters and developers.
So, after analysis, YSlow assigns several grades (I think from ‘A’ to ‘Z’) and supplies good pratices and advices to optimize your site.
… for example, we have a grade “F” on “Add Expires headers” point:
… more, YSlow describes the problem and optimisation to do:
Web pages are becoming increasingly complex with more scripts, style sheets, images, and Flash on them. A first-time visit to a page may require several HTTP requests to load all the components. By using Expires headers these components become cacheable, which avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often associated with images, but they can and should be used on all page components including scripts, style sheets, and Flash.
There are also others tabs:
- the “Components” tab supplies the number of components (document, js, css, image…) and their size/weight in the analyzed page through a table:
- the “Statistics” tab is interesting because it supplies charts concerning the analyzed page: