HTTP Status Codes Reference

HTTP status codes are three-digit numbers a server returns with every response to tell the client what happened to its request. A code of 200 means the request succeeded, 404 means the page was not found, and 500 means the server hit an error. This reference lists every standard status code defined by the Internet Engineering Task Force, grouped by class, with a plain-English explanation of what each one means and a link to the specification that defines it. You can search by number, by name, or by a word from the description.

Status codes fall into five classes identified by their first digit. The 1xx class is informational and signals that the request was received and processing continues. The 2xx class means success, so the request was received, understood, and accepted. The 3xx class is redirection, telling the client the resource lives somewhere else or has not changed. The 4xx class is a client error, meaning the request was malformed or not allowed. The 5xx class is a server error, where the request was valid but the server failed to fulfil it. Knowing the class alone tells you whether to fix your request or look at the server.

Developers reach for a status code reference constantly. Front-end engineers debug why an API call returns 401 instead of 200, back-end developers decide whether to send 400 or 422 for a validation failure, and SEO specialists check that a moved page returns 301 rather than 302 so search engines transfer its ranking. This tool runs entirely in your browser, so searches are instant and nothing is sent to a server. It works offline once loaded and is free with no account required, making it a fast tab to keep open while building or debugging any web service.