Debug PageSpeed filters

Overview

If you wish to see debugging information about a certain page, perhaps trying to find out why an asset isn’t being optimised by Pagespeed, you can view source on the page you are trying to debug.

Implementation

  1. View the source of the page.
  2. Add this querystring ?PageSpeedFilters=+debug to the view-source URL.
    • If the URL of the page already contains querystrings, use &PageSpeedFilters=+debug.

You should now see comments next to an assets that indicate reasons why is was not optimised. e.g.

<!--deadline_exceeded for filter CacheExtender--><!--deadline_exceeded for filter Javascript-->

or

<!--Resource headers are preventing rewriting of https://www.example.com/123.gif-->