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HTTP Status Code Lookup

Find out what any HTTP status code means and which response category it falls into.

How it is calculated

An HTTP status code is a three-digit number a server sends with every response. The first digit gives the class: 1xx informational, 2xx success, 3xx redirection, 4xx client error and 5xx server error. The tool accepts a whole number from 100 to 599, looks it up in a built-in list of the commonly used codes (about 40, such as 200, 301, 404 and 503), and shows the standard reason phrase and the class. A code in range that is not in the list is shown as Unknown, but its class is still given from the first digit. Anything that is not three digits, or is outside 100–599, returns no result.

Worked example

A browser shows an error for a missing page, and the code is 404. The first digit is 4, so the class is Client Error: the request itself is the problem. The list gives the reason phrase Not Found. The server was reachable and working, but there is nothing at that address.

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Common mistakes

  • Treating every 4xx as the visitor's fault. It means the request was refused, but a broken link on your own site also produces a 404.
  • Using 302 where a permanent move needs 301 (or 308). Search engines treat the two differently.
  • Confusing 401 and 403. 401 means credentials are missing or wrong, while 403 means you are known but not allowed.
  • Entering the text of the error instead of the number, or a code like 20 or 6000, which returns nothing.
  • Assuming an unlisted code is invalid. Custom and rare codes exist and are classed by their first digit.

About this calculator

This tool looks up any HTTP status code and returns its standard reason phrase (like "Not Found" for 404 or "Moved Permanently" for 301) along with its category — 1xx informational, 2xx success, 3xx redirection, 4xx client error, or 5xx server error — as defined in the HTTP specification (RFC 9110).

Web developers use it while debugging API responses and server logs, SEO professionals use it to understand redirect chains and crawl errors, and students learning web development use it as a quick reference instead of digging through the RFC.

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Comments (1)

  • Editorial team

    Two codes are often swapped: 401 means the request lacked valid credentials, while 403 means the server understood who you are and still refuses. Likewise, 301 is a permanent redirect and 302 a temporary one, which affects how caches and search engines treat the old address. The tool lists about 40 common codes and shows Unknown for the rest. Which codes would you like added to the list?

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