How it answers, right now
A live request to the site itself: how fast it answers, what status it returns, which HTTP version it speaks, and what software it admits to running. Free, no signup, 5 checks a day.
5 free checks a day. No signup, no key.
The floor under every page load
A live request, once
The check makes one real request to the site and times it: status code, response time, HTTP version, server software. Slow here is slow everywhere — this is the floor under every page load the site will ever do.
HSTS and the https redirect
HSTS tells browsers to refuse plain HTTP for a window of time; the redirect check confirms plain HTTP either answers and redirects or does not answer at all. Both are the difference between 'https works' and 'https is enforced'.
Software disclosure
The Server header names the software behind the site. 'Hidden' is not a failure — omitting it is the quieter habit — but many servers advertise their version publicly and have done so for years.
Typed failures, not silence
A 5-second timeout and typed errors mean a slow server shows up as a timeout with a reason, not as a blank row and a guess.