HTTP Status Codes — Complete Reference
Look up any HTTP status code. Search by number or keyword to see what it means, when servers send it, and what usually causes the common errors.
How to use the status code reference
- Type a code (like 404) or a word (like "redirect").
- Filter by class to browse a group.
- Each entry explains the meaning and common causes.
The five classes of status codes
The first digit tells you the category: 1xx informational, 2xx success, 3xx redirection, 4xx client errors (the request was wrong) and 5xx server errors (the server failed to handle a valid request). Clients that do not recognize a specific code treat it like the x00 code of its class.
For SEO, the important ones are 200 (OK), 301 (permanent redirect, passes ranking signals), 302/307 (temporary redirect), 404 and 410 (not found and gone), and 5xx errors, which, if they persist, cause search engines to slow crawling and eventually drop pages.
Definitions follow RFC 9110 (HTTP Semantics) and related RFCs. 418 "I'm a teapot" is a real registered joke code from an April Fools RFC.
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Frequently asked questions
What is the difference between 401 and 403?
401 means you are not authenticated (log in); 403 means you are authenticated but not allowed.
301 or 302?
301 for permanent moves, so search engines transfer ranking; 302 or 307 for temporary ones.
What causes a 502 Bad Gateway?
A proxy or load balancer got an invalid response from the upstream server, often because the app crashed, restarted or timed out.
Is 404 bad for SEO?
Not in itself; removed pages should return 404 or 410. Broken internal links to 404 pages are worth fixing.