HTTP Status Code Reference

HTTP status codes are three-digit numbers returned by a web server in response to a client's request. They indicate whether the request was successful, redirected, resulted in a client error, or caused a server error. Understanding these codes is essential for web development, API integration, and debugging.

1xx Informational

These codes indicate that the server has received the request and the client should continue. 100 Continue is the most common, telling the client to proceed with sending the request body. 101 Switching Protocols is used for WebSocket upgrades.

2xx Success

These codes indicate that the request was successfully received, understood, and accepted. 200 OK is the standard success response. 201 Created confirms a new resource was created (common in REST APIs after POST). 204 No Content indicates success with no response body.

3xx Redirection

These codes indicate that further action is needed to complete the request. 301 Moved Permanently is used for permanent URL redirects (important for SEO). 302 Found and 307 Temporary Redirect are used for temporary redirects. 304 Not Modified tells the browser to use its cached version.

4xx Client Error

These codes indicate an error on the client side. 400 Bad Request means the request was malformed. 401 Unauthorized requires authentication. 403 Forbidden means the server understood the request but refuses to fulfill it. 404 Not Found is the most well-known error code. 429 Too Many Requests indicates rate limiting.

5xx Server Error

These codes indicate that the server failed to fulfill a valid request. 500 Internal Server Error is a generic server error. 502 Bad Gateway means the server received an invalid response from an upstream server. 503 Service Unavailable indicates the server is temporarily overloaded or under maintenance. 504 Gateway Timeout means the upstream server did not respond in time.