HTTP status codes are three-digit numbers returned by a web server in response to a client request. They indicate whether the request was successful, redirected, or resulted in an error. Understanding these codes is essential for web developers, API designers, DevOps engineers, and anyone troubleshooting web applications.
1xx (Informational): The request was received and the server is continuing to process it. These are rarely seen by end users.
2xx (Success): The request was successfully received, understood, and accepted. 200 OK is the most common.
3xx (Redirection): The client must take additional action to complete the request, usually following a redirect URL.
4xx (Client Error): The request contains bad syntax or cannot be fulfilled. The problem is on the client side.
5xx (Server Error): The server failed to fulfill a valid request. The problem is on the server side.
200 OK — Standard success response.
201 Created — Resource was created (common in REST APIs after POST).
301 Moved Permanently — URL has permanently changed; search engines update their links.
302 Found — Temporary redirect; the original URL should still be used.
400 Bad Request — The server cannot process the request due to malformed syntax.
401 Unauthorized — Authentication is required and has failed or not been provided.
403 Forbidden — The server understood the request but refuses to authorize it.
404 Not Found — The requested resource could not be found on the server.
429 Too Many Requests — Rate limiting; the client has sent too many requests.
500 Internal Server Error — A generic server error when no more specific message is suitable.
502 Bad Gateway — The server received an invalid response from an upstream server.
503 Service Unavailable — The server is temporarily overloaded or under maintenance.