HTTP Status Code Reference

What this reference covers

Every HTTP response starts with a three-digit status code that tells the client how the server handled the request. When a page fails to load, an API call returns something unexpected or a monitoring alert fires, the code is usually the first clue. This page collects 19 codes that web developers, API integrators and site owners see most often and explains each one in plain language: what it means, the situations that typically produce it, and which section of the HTTP specification defines it. It is a quick lookup, not the complete registry.

How to use it

1. Type a number such as 404 or a word such as timeout, token or proxy into the search box. The search looks through code numbers, names, descriptions and the listed causes, and a counter shows how many entries match. Press / to jump to the box, and the ✕ button to clear it.
2. Narrow the list with the category tabs (All, 1xx Info, 2xx Success, 3xx Redirect, 4xx Client Error, 5xx Server Error), or click one of the class tiles to jump straight to that group.
3. Click any row to expand it. You will see a longer explanation, a list of common causes and the RFC section reference. Click the row again to collapse it.
4. Use the causes as a checklist while you debug, then confirm against your own server logs or the browser's network panel.

Reading a status code

The first digit sets the class. 1xx responses are interim messages sent before the final answer, 2xx means the request succeeded, 3xx asks the client to look somewhere else, 4xx says the request itself was the problem, and 5xx says the server failed on a request that looked valid. The last two digits pick the exact meaning inside the class. A client that receives a code it does not recognise is expected to treat it like the x00 code of the same class, so an unknown 4xx is handled like 400.

Pairs that are often confused

• 401 vs 403. 401 means no valid credentials were supplied, so logging in or sending a fresh token may fix it; the server must send a WWW-Authenticate header. 403 means the server knows who you are, or does not care, and still refuses.
• 301 vs 302. 301 marks a permanent move, and browsers and search engines are expected to switch to the new URL. 302 is temporary, so the original URL stays the one to use.
• 502 vs 504. Both come from a gateway or proxy. 502 means the upstream server sent back an invalid response; 504 means it did not answer in time.
• 500 vs 503. 500 is an unexpected failure such as an unhandled exception. 503 signals a temporary overload or maintenance, often with a Retry-After header.

Sources and limitations

The explanations are a hand-written summary bundled with the page, not a live feed. Each entry cites the RFC section that defines the code: RFC 9110 (HTTP Semantics, the current standard that replaced RFC 7231, 7232 and 7235) for most of them, and RFC 6585 for 429 Too Many Requests. The full list of registered codes is maintained by IANA in the HTTP Status Code Registry, and it includes many codes this page does not describe, for example 202 Accepted, 206 Partial Content, 307 and 308 redirects, 409 Conflict, 410 Gone, 422 Unprocessable Content and 501 Not Implemented. The listed causes are typical examples; real servers, frameworks and CDNs sometimes use codes in their own way, so always check the response body and logs as well.

The search runs entirely in your browser against the list shipped with the page. Nothing you type is sent anywhere or saved.

Frequently asked questions

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