There is a simple trick to find out if a certain website uses the CDN Cloudflare or not. All we need to do is to add /cdn-cgi/trace at the end of the (sub)domain name:
https://www.cloudflare.com/cdn-cgi/trace
When the site uses Cloudflare, we get a result back that looks like this:
fl=64f79
h=www.cloudflare.com
ip=xxx.xxx.xxx.xxx
ts=1721932764.526
visit_scheme=https
uag=Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
colo=ZRH
sliver=none
http=http/3
loc=CH
tls=TLSv1.3
sni=plaintext
warp=off
gateway=off
rbi=off
kex=X25519Kyber768Draft00
Otherwise, we end up with a 404 error:
