The most surefire way to know if a site is behind Cloudflare (orange cloud is on) is by hitting /cdn-cgi/trace (e.g. https://news.ycombinator.com/cdn-cgi/trace

The most surefire way to know if a site is behind Cloudflare (orange cloud is on) is by hitting /cdn-cgi/trace (e.g. https://news.ycombinator.com/cdn-cgi/trace https://news.ycombinator.com/cdn-cgi/trace) which is the debug output from Cloudflare’s HTTP server. There’s no way to my knowledge that route can be disabled or overriden. Anyway, no, HN is not on Cloudflare, at least at the moment.