HTTP Status Codes

HTTP status codes are used to communicate the status of a request between the client and the server. These codes are divided into five categories:

1xx Informational

1xx status codes inform the client that the request has been received and is continuing to be processed.

100 Continue: Indicates that the initial part of the request has been received and the client should continue with the request.
101 Switching Protocols: Indicates that the server is switching protocols as requested by the client.

2xx status codes indicate that the request was successfully received, understood, and accepted.

200 OK: The request was successful.
201 Created: The request was successful and a new resource was created.
202 Accepted: The request has been received but not yet acted upon.
204 No Content: The request was successful but there is no content to send in the response.

3xx status codes indicate that further action needs to be taken by the client to complete the request.

301 Moved Permanently: The requested resource has been permanently moved to a new URL.
302 Found: The requested resource is temporarily available at a different URL.
304 Not Modified: The requested resource has not been modified since the last request.

4xx status codes indicate that the client made an error in the request.

400 Bad Request: The request could not be understood by the server due to malformed syntax.
401 Unauthorized: The request requires user authentication.
403 Forbidden: The server understood the request, but is refusing to fulfill it.
404 Not Found: The server has not found anything matching the requested URL.
405 Method Not Allowed: The method specified in the request is not allowed for the resource.
409 Conflict: The request could not be completed due to a conflict with the current state of the resource.
429 Too Many Requests: The client has sent too many requests in a given amount of time.

5xx status codes indicate that the server encountered an error while processing the request.

500 Internal Server Error: The server encountered an unexpected condition which prevented it from fulfilling the request.
501 Not Implemented: The server does not support the functionality required to fulfill the request.
502 Bad Gateway: The server received an invalid response from an upstream server.
503 Service Unavailable: The server is currently unable to handle the request due to temporary overload or maintenance.
504 Gateway Timeout: The server did not receive a timely response from an upstream server.

200 OK: Use when the request is successfully processed and data is returned.
201 Created: Use when a new resource is successfully created, such as a new user registration.
204 No Content: Use when the request is successful but there is no content to return, such as after a resource is deleted.
400 Bad Request: Use when there is an error in the request from the client's side, such as missing parameters.
401 Unauthorized: Use when authentication is required.
403 Forbidden: Use when the client is authenticated but does not have permission to access the resource.
404 Not Found: Use when the requested resource is not found on the server.
409 Conflict: Use when there is a conflict with the current state of the resource, such as duplicate data entry.
500 Internal Server Error: Use when there is an unexpected error on the server's side.
503 Service Unavailable: Use when the server is temporarily unavailable due to overload or maintenance.

These guidelines provide a basic understanding of when to use each status code, although specific use cases may vary.