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What do the status code ranges mean?
- 1xx — Informational: request received, still processing
- 2xx — Success: the request worked as expected
- 3xx — Redirection: further action needed to complete the request
- 4xx — Client error: something is wrong with the request itself
- 5xx — Server error: the server failed to fulfill a valid request
Frequently confused codes
401 means the request lacks valid authentication credentials; 403 means the credentials are fine but access is forbidden. 301 is a permanent redirect that search engines pass ranking to; 302 is temporary and shouldn't be treated as permanent. 502 means an upstream server sent an invalid response; 503 means the server is temporarily unable to handle the request (often due to overload or maintenance).