YSlow: Add Expires headers

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.

YSlow recommends:

There are two things in this rule:

For static components: implement "Never expire" policy by setting far future Expires header
For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests

Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.)

Have an idea for this recommendation?

Feel free to contact us with your suggestions, links or ideas!