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About this tool
Understand HTTP status codes with simple, clear explanations instantly.
The HTTP Status Code Explainer looks up any HTTP response status code and tells you what it means, which of the five RFC 9110 classes it belongs to — 1xx informational, 2xx success, 3xx redirection, 4xx client error, 5xx server error — and, for the common failures, what usually fixes it. Type a number such as 404 or click one of the quick codes like 200, 301, 403 or 503, and the panel explains the code in plain language. It is aimed at developers, QA testers and site owners staring at a status line in a browser devtools panel, a server log or an API response.
Open HTTP Status Code Explainer on AltFTool — it loads instantly in your browser.
Type a number into the Enter HTTP Status Code (e.g., 404) box, or click a quick code such as 200, 301, 403 or 503.
Press Explain, or pick a card from the grid of common codes — 204, 307, 409, 418, 429 and 502 among them.
The panel names the code and its short title, such as 404 — Not Found, with a 4xx Client Error class badge and a plain-language explanation.
Every code is labelled with its 1xx–5xx family, so you immediately know whether to look at your request or at the server.
Common failure codes come with concrete next steps — respect Retry-After and back off exponentially for 429, check upstream health or raise the timeout for 504.
Enter any number and the class is still derived from its range, so an unusual or vendor-specific code is not a dead end.
There are five classes, decided by the first digit: 1xx informational (the request was received and processing continues), 2xx success, 3xx redirection, 4xx client error (the request was faulty), and 5xx server error (the request was fine but the server failed). Anything outside 100–599 is not a valid HTTP status.
301 Moved Permanently says the resource has a new URI and callers should update their links; 302 Found and 307 Temporary Redirect both say the move is temporary and the original URI should keep being used. The practical distinction is that 307 preserves the original request method and body, whereas 302 is widely implemented as switching a POST to a GET.
Back off and retry later, using exponential backoff and honouring the Retry-After header if the response includes one. 429 Too Many Requests means you exceeded a rate limit in a given window, so retrying immediately usually extends the block rather than clearing it.
It is a real registered code but a deliberate joke, originating in the 1998 Hyper Text Coffee Pot Control Protocol April Fools RFC. It means the server refuses to brew coffee because it is a teapot; no production API should return it, and there is nothing to fix if you see it.