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



How it works

Varnish adds the following header to HTTP responses that it handles:


You should be able to see that Varnish is working on your site by inspecting the response headers and looking for that header. Or, enter your URL above and my tool will find it for you :-)

Sometimes, Varnish is up and running but not working properly. This tool also checks the


header to ensure that the content being served is cached - indicated by a value greater than 0.

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

What is Varnish?

Varnish Cache is a reverse proxy caching software. It works by sitting in front of your server software (e.g. Apache/NGINX) and caching its content. It's very simple to set up and very fast. Varnish receives all of your incoming connections and, if it doesn't have a cached version of the content, passes them to your server software. Once it has a copy of the content in its cache, it returns it without sending the request to your server software (and it does so damn fast).

For a really good explanation of how Varnish works, check out the developer's introduction to Varnish, or have a look at their excellent video.