

The Clacks Overhead plugin for Chrome and the GNU Terry Pratchett extension for Firefox both light up when they detect the HTML meta tag or HTTP header. You can check that the meta tag is visible by viewing your site’s HTML source and searching for “GNU Terry Pratchett”.

To send the HTTP header and continue to use a caching plugin, add the header at the server level. Note that the HTTP header is not sent if you use a page caching plugin.
