Glossary · Speed and HTTP
An HTTP status code is the three-digit number a server returns with every response to say how a request went: 2xx for success, 3xx for redirects, 4xx for client errors and 5xx for server errors.
The first digit sets the class, defined in RFC 9110: 1xx informational, 2xx successful, 3xx redirection, 4xx client error and 5xx server error. A client that doesn’t know a specific code treats it like the x00 code of its class.
For monitoring, the code is the first sign of health. 5xx means the server or something in front of it failed: 500 an application error, 502 and 504 a problem between a proxy and the origin server, 503 overload or maintenance. 4xx usually means the request was wrong, but a 403 or 429 for a monitoring check often means a firewall or rate limit is blocking it, not that the site is down.
A 200 doesn’t prove a page works: an error page served with 200 is still an error. Check the content too, with keyword monitoring.
Uptimecheck HTTP monitors accept 200–399 by default, follow up to 10 redirects and judge the final answer. Set your own expected codes or ranges, such as 200-299 or 200,301, and add a keyword or JSON check for pages that can fail with a 200.
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Guides 7 min read
Which HTTP status codes mean your site is down, which are fine and which depend on the endpoint. A monitoring-focused cheat sheet covering 1xx to 5xx, redirects, 401, 403, 429 and 5xx errors.
ReadGuides 5 min read
A 500 Internal Server Error means the application failed while handling the request. Where to find the real error message, the causes behind most 500s and how to make sure you hear about them first.
ReadGuides 6 min read
A 502 Bad Gateway means a proxy, load balancer or CDN got no valid answer from the server behind it. How to find which layer failed, fix the usual causes and catch the next 502 before customers do.
Read5xx codes, and no answer at all, such as a timeout or a refused connection. Some 4xx codes, like a 404 on the home page, also mean visitors can’t use it.
Usually yes. Monitors follow redirects and judge the final page; a redirect loop or a redirect to an error page is a failure.
The free HTTP status codes reference has a page per code, with what it means, what usually causes it and what to do about it.
Set up your first monitor in under a minute, or look around the live demo first.
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