HTTP Status Codes

HTTP status codes are 3-digit numbers returned by a server to indicate the result of an HTTP request.

1xx – Informational Responses

These indicate that the request has been received and is still being processed.

• 100 Continue → Server received request headers, continue sending body.
• 101 Switching Protocols → Client requested a protocol change (e.g., WebSockets).

2xx – Success Responses

The request was successfully received, understood, and processed.

• 200 OK → Request was successful.
• 201 Created → A new resource was successfully created (e.g., after a POST request).
• 202 Accepted → Request accepted but not yet processed.
• 204 No Content → Request was successful, but there is no response body.

3xx – Redirection Responses

The client must take additional action to complete the request.

• 301 Moved Permanently → The resource has moved to a new URL permanently.
• 302 Found → Temporary redirection to another URL.
• 304 Not Modified → The cached version is still valid (no need to download again).

4xx – Client Errors

The request contains errors or the client doesn’t have permission.

• 400 Bad Request → Request has invalid syntax.
• 401 Unauthorized → Authentication is required (e.g., missing or invalid token).
• 403 Forbidden → Client does not have permission (even if authenticated).
• 404 Not Found → Requested resource does not exist.

405 Method Not Allowed → HTTP method (GET, POST, etc.) is not allowed for this resource.

5xx – Server Errors

The server failed to fulfill a valid request.

• 500 Internal Server Error → General server error.
• 502 Bad Gateway → Server received an invalid response from the upstream server.
• 503 Service Unavailable → Server is temporarily unavailable (e.g., maintenance).
• 504 Gateway Timeout → Server didn’t receive a response in time from another server.