Use the free HTTP Status Code Lookup below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What Is an HTTP Status Code?
Every time your browser asks a server for a page, the server answers with a three-digit status code before it sends anything else. The code is a short summary of what happened. The first digit tells you the class: 1xx means informational, the server got the request and is still working; 2xx means success; 3xx means redirection, look somewhere else; 4xx means the client did something wrong; 5xx means the server failed. The other two digits name the specific case, like 404 for not found or 500 for an internal error.
Status codes matter because they are the language servers and browsers share. A browser that gets a 301 knows to follow the new address and remember it. A search engine that gets a 404 knows the page is gone. A script that gets a 429 knows to slow down. When you build or debug a website, reading the code is usually faster than guessing from the page you see, because the page can lie: a friendly error page can hide a 500, and a blank page can hide a 404.
How to Use the Lookup
Type a code, like 404, or a word, like timeout, into the search box, and the table filters at once. You can also filter by class, for example all 5xx server errors. Click any row for a plain-language explanation of that code. The whole table ships with the page, so nothing is sent to a server while you search, and the tool works even on a slow connection.
Start with the first digit when you see a code you do not know. A 4xx code means the request was the problem: a wrong URL, missing login, or a request the server refuses. A 5xx code means the server is at fault or overloaded, and retrying the same request may work later. A 3xx code usually means the resource moved, and the browser should already have followed it, so a visible 3xx often points to a redirect loop or a misconfigured rule.
The Codes You Will Meet Most
Code 200 means success, the normal answer for a page that loaded. Code 201 means a new resource was created, common after a form that creates something. Code 204 means success with no content to show, common for actions like deleting. Code 301 means moved permanently, and search engines should update their records. Code 302 means moved temporarily, and the old address stays valid. Code 304 means not modified, so the browser can reuse its cached copy, which saves bandwidth.
Code 400 means the request itself was malformed. Code 401 means you need to log in first. Code 403 means the server refuses, even with a login, because you lack permission. Code 404 means the resource is not there: check the URL for typos, or the page moved or was deleted. Code 429 means you sent too many requests too fast, and you should wait before retrying. Code 500 means the server hit an unexpected problem, and the fix is on the server side. Code 502 means a gateway got a bad reply from the server behind it, and 503 means the server is temporarily unavailable, often during maintenance or overload.
Debugging With Status Codes
When a page fails, open your browser developer tools, go to the Network tab, reload, and read the status column. That one column usually splits the problem in half: client side or server side. If you see a 404 for one file, the file path is wrong or the file is missing. If you see a 500, read the server logs, because the browser cannot tell you more. If you see a redirect chain of several 301s and 302s, one rule is pointing at another in a loop.
For your own sites, choose codes deliberately. Return 404 for missing pages, not 200 with an error message, or search engines will index your error page as content. Return 410 for pages removed on purpose, so search engines drop them faster. Return 503 during planned maintenance, with a Retry-After header, so search engines know to come back. Status codes are small, but they carry real meaning, and using them well makes your site easier to debug, easier to index, and easier for other developers to work with.