Performance · 15 points
Server response time
One check, stated three ways: what we measure, what would make it wrong, and how to confirm it yourself.
What this measures
Time to first response headers, measured from our server, once.
Where this check can be wrong
This is one sample from one region, on one request. Cold caches, CDN pops and a busy minute all move it more than your code does. It is not Core Web Vitals.
Verify it without taking our word for it
curl -w 'ttfb=%{time_starttransfer}s total=%{time_total}s\n' -o /dev/null -s https://your.site, run it five times, and look at the spread.