Each Railgun enabled request’s response header will show Railgun stats to measure the improvements What is Railgun? – Cloudflare Help Center
Is Railgun running on my site?
When a request is handled by Railgun, Cloudflare inserts a header with diagnostic information to track the protocol.
To view the following Railgun headers, use a browser that allows you to examine header information.
Google Chrome: View > Developer > Developer Tools menu. You can also install Cloudflare’s Claire extension.
Safari: Develop > Show Web Inspector menu
Firefox: Install Firebug
Microsoft Internet Explorer: You can use a tool like Fiddler
When looking for the header information, you should see Cloudflare headers similar to the following response:
cf-railgun : e95b1c46e0 0.02 0.037872 0030 9878
The CF-Railgun header has up to five codes separated by a space. In order, these codes and their corresponding values from the example of cf-railgun : e95b1c46e0 0.02 0.037872 0030 9878 listed above are:
- Railgun Request ID: e95b1c46e0 (internal process number that allows us to track what connection handled a request )
- Compression Ratio: 0.02 (the size of the response after Railgun’s delta compression expressed as a percentage)
- Origin Processing Time: 0.037872 (that Railgun waits for the origin web server to generate the page)
- Railgun Flags: 0030 (how a request was processed)
- Version Number: 9878 (indicates the version of the Railgun Listener software on the origin server’s network)
So a Compression Ratio of 0.02 means Railgun saved 99.98% of dynamic HTML page’s bytes from being sent between origin and CF edge server. Remember Railgun optimises only the HTML bytes sent from a non-cached dynamic HTML request and that is only a small part of the overall page load speed of a page - though still important due to Google Core Web Vital metrics all relying on how fast the HTML is parsed/rendered first.