What is an HTTP status code?
An HTTP status code is the three-digit number a server sends with every response to say how the request went: 2xx success, 3xx redirect, 4xx client error, 5xx server error.
In more detail
- 200 OK. 301 moved permanently; 302 found, a temporary move; 304 not modified, use your cached copy.
- 403 forbidden; 404 not found; 410 gone for good; 429 too many requests.
- 500 internal server error; 502 bad gateway, a server in front got a bad answer from the one behind it; 503 service unavailable, often maintenance or overload; 504 gateway timeout.
For monitoring, 5xx answers mean the site is failing; 4xx answers mean that particular page is missing or blocked.
Worked example
Asking for https://example.com/old-page returns 301 with Location: https://example.com/new-page, which returns 200. Visitors and search engines end up on the new page, and the permanent redirect tells search engines to update their index.
See also
Related terms: Redirect chain and Downtime. Free tool: DNS and HTTP headers. How OwlHound helps: Broken link monitoring. All terms: monitoring glossary.
Frequently asked questions
What is the difference between 301 and 302?
301 says the move is permanent, so search engines move their index to the new address. 302 says it is temporary.
Is a 404 bad for SEO?
A 404 for a page that really is gone is normal. It costs you when the missing page had links pointing to it: redirect it to the closest page instead.
What does 503 mean?
Service unavailable: the server is up but not handling requests, usually during maintenance or under too much load.
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