Here's the user agent we'll use (change it if you like):



How it works

Google's mod_pagespeed tool adds one of two headers to HTTP responses, depending on whether the server is Apache or Nginx.

For Apache servers, it adds:


And for Nginx servers:


You can see if mod_pagespeed is working on your site by inspecting the response headers and looking for either value, or you can use my little free tool and enter your URL below :-)

Found it useful? Give a one-off £2 donation to Save the Children to say thanks:

What is mod_pagespeed?

mod_pagespeed is an Apache and Nginx module from Google that assists you in speeding up your website by automatically applying recommended optimisations to web pages and their assets (CSS, JavaScript, images).

One of mod_pagespeed's greatest features is the fact that it doesn't require you to manually perform any of these tasks! Once installed, it will automatically begin optimising your website and provides you with extra configuration options should you wish for greater control over how it optimises.

Among the 40+ optimisation filters available in mod_pagespeed are:

  • optimisation, compression and resizing of your images;
  • concatenation, minification, and inlining of your CSS and JavaScript;
  • cache extension, domain sharding, and domain rewriting; and
  • deferred loading of JavaScript and image resources.