HTTP Status Code Reference
Plain English explanations for every HTTP status code — what it means, when to use it, common causes and real code examples.
1xx Informational
Continue
Server received request headers, client should proceed.
Switching Protocols
Server is switching to the protocol requested by the client.
Processing
Server is processing the request but no response is available yet.
Early Hints
Preload resources while the server prepares the final response.
2xx Success
3xx Redirection
Moved Permanently
Resource has permanently moved to a new URL.
Found
Resource temporarily moved to a different URL.
Not Modified
Resource has not changed — use the cached version.
Temporary Redirect
Temporary redirect — method and body must not change.
Permanent Redirect
Permanent redirect — method and body must not change.
4xx Client Error
Bad Request
Server cannot process the request due to a client error.
Unauthorized
Authentication is required — client is not authenticated.
Forbidden
Server understood the request but refuses to authorize it.
Not Found
The requested resource does not exist.
Method Not Allowed
HTTP method is not supported for this endpoint.
Request Timeout
Server timed out waiting for the client to send the request.
Conflict
Request conflicts with the current state of the resource.
Gone
Resource permanently deleted and will not return.
Length Required
Content-Length header is required.
Content Too Large
Request body is larger than the server will accept.
Unsupported Media Type
Content-Type is not supported by the server.
Unprocessable Entity
Request is well-formed but contains semantic errors.
Too Many Requests
Client has sent too many requests — rate limited.
5xx Server Error
Internal Server Error
Server encountered an unexpected error.
Not Implemented
Server does not support the functionality required.
Bad Gateway
Upstream server returned an invalid response.
Service Unavailable
Server is temporarily unavailable — overloaded or down for maintenance.
Gateway Timeout
Upstream server did not respond in time.
Insufficient Storage
Server cannot store the representation needed to complete the request.
About HTTP Status Codes
HTTP status codes are three-digit numbers returned by a server in response to a client request. They are grouped into five classes: 1xx informational responses, 2xx successful responses, 3xx redirection messages, 4xx client error responses, and 5xx server error responses.
Understanding the difference between similar codes — like 401 vs 403, or 400 vs 422, or 502 vs 504 — helps you debug APIs faster and build more informative error responses. Each code is defined in an RFC (Request for Comments) document published by the IETF.