Is It Down
Type an address. We ask for it from here, on a different network from yours, and tell you exactly what we get back.
Why ask someone else
Reloading it yourself cannot tell the two cases apart. If it answers here and not there, the problem is between your machine and the site — your DNS, your network, your cache, your provider — and that is a completely different phone call.
What this does not tell you
One check from one place. A site can be up here and unreachable from another country, and a site that answers can still be serving the wrong thing. For continuous watching — checked over and over, with an alert when it stops answering — that is the monitoring below.
Want to be told, instead of asking
This is a one-off look. Watching it every few minutes and telling you when it goes down is what monitoring does.