There are a few different ways to see if Cloudflare is active on a website.
For more information on how to examine your website’s headers, see the following article:
Viewing the headers of your website
You’ll need a mechanism to verify these headers to see if Cloudflare is enabled and operating on your website because Cloudflare puts header information into requests.
You’re looking for the following special Cloudflare header while looking at these headers: