HTTP Status Codes

HTTP status codes are three-digit numbers a server returns with every response to tell the client how the request went. They are organized into five classes by their first digit, and knowing the class alone tells you most of the story. The 1xx codes are informational and rarely seen in app code; 2xx mean success (200 OK, 201 Created, 204 No Content); 3xx mean redirection (301 Moved Permanently, 302 Found, 304 Not Modified); 4xx mean the client sent something wrong (400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 429 Too Many Requests); and 5xx mean the server failed while handling an otherwise valid request (500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout). This reference lets you search every code by number or keyword and filter by class, with a plain-English description for each, so you can diagnose an API or a browser request without digging through the RFCs. A frequent point of confusion is 401 versus 403. They sound similar but mean different things: 401 Unauthorized actually means unauthenticated, the server does not know who you are and you should supply or refresh credentials; 403 Forbidden means the server knows who you are but you are not allowed to do this, so retrying with the same credentials will not help. Another common mix-up is 301 versus 302: 301 is permanent and tells browsers and search engines to update their links, while 302 is temporary and they keep the original. The reference also covers the less common but useful codes, including 422 Unprocessable Content, the WebDAV range (207, 423, 424, 507), 451 Unavailable For Legal Reasons, and 418 I'm a teapot, which began as an April Fools joke in RFC 2324 yet still appears in some services. This lookup is a static reference that runs entirely in your browser.