Guides to downtime, errors and monitoring
Five subjects, each with a hub page that frames the problem and a set of articles that go into it properly. Written to be read once and remembered, not to be skimmed for a keyword.
Website downtime
A complete guide to website downtime - How outages actually happen, how to tell a real one from a local problem, and what to do about it.
Error codes explained
What each HTTP status code and browser error actually means, who is responsible for it, and whether waiting will fix it.
Connection troubleshooting
DNS, Wi-Fi, ISP outages, VPNs and the local causes that make a perfectly healthy website look like it is down.
Uptime and monitoring
How uptime is measured, what an SLA actually promises, how status pages work, and how to monitor something yourself.
Major outage history
Detailed accounts of the internet's largest outages - What broke, why it cascaded so far, and what the industry changed afterwards.
Where to start, depending on what just happened
A site will not load and you do not know why
Begin with is it down for everyone or just me, which settles the first question in about a minute, then run the site through our checker to see which stage of the request actually failed.
You have an error code on screen
Go straight to the error code guides. A 502 and a 504 look identical to a reader and mean different things about who can fix it, and the code narrows the cause more than anything else available to you.
Everything is broken, not one site
That is usually your own connection or your provider rather than the whole internet. The troubleshooting hub works through the causes in order of how often each one turns out to be the answer, starting with DNS.
You are trying to measure or promise uptime
Read uptime monitoring for how measurement actually works, and use the uptime calculator to see what a percentage in a contract really permits. Our own methodology sets out what our figures include and, more usefully, what they cannot see.
You want to know what a big outage looked like
The outage history hub reconstructs the largest incidents on record: What broke, what the public saw, and how long recovery actually took once the fix was known.