When a site misbehaves, the first useful answer almost always comes from a check run outside your own machine, and the fastest way to tell a real outage from a local problem is to repeat the check from a different network. The guides in this section cover the checks people run, what each command prints, and how to read the result.
Most incidents come down to a handful of questions. Is the site down for everyone or just for me? How fast does it load, and from where? Who hosts it, and who is the registrar? Is a port reachable from outside the firewall? Is our sending IP on a blacklist? Has the certificate expired, or is a DNS change simply not everywhere yet? Each of those has a free instant check on this site that answers it in a few seconds. Each also has a command you can run yourself when you want the raw output: dig, curl, openssl s_client, nc. The guides show both, because the tool answers from many locations at once and the command answers from exactly where you are standing. Comparing the two is often the diagnosis.
No single check tells you when something changed. A check answers "right now", from wherever it ran, and only if you happen to run it. HostTracker has been monitoring websites since 2004 and now watches over 500,000 websites from 300+ checkpoints in 158 cities, running the same checks on a schedule and sending an alert by email, SMS, voice call, Slack, Telegram and more when a result changes. The guides below start from the symptom. To see whether a site is answering at this moment, run the website down checker.