A three-digit number is all a server sends when something goes wrong, and the difference between 401 and 403, or between 301 and 308, decides what you should do next. This lookup turns any HTTP status code into a plain-language explanation: what the code means, which class it belongs to, and the usual cause, so you can stop guessing from memory. It covers the standard codes from the 100s through the 500s, and for codes it does not list by name it still identifies the class, because knowing that a code is a server error rather than a client error already narrows the search. Developers debugging APIs, site owners reading error logs, and students learning the web all reach for the same reference, and this one keeps it in a single search box.
Quick Answer: Enter any HTTP status code and instantly see what it means and what usually causes it.
Free Online Tool
HTTP Status Code Lookup
Three digits in, a plain explanation out.
How to Use the HTTP Status Code Lookup
- Type a three-digit HTTP status code, for example 404.
- Press Look Up to see its name and meaning.
- Read the class note to tell client errors from server errors.
- Use the usual-cause hint to decide your next debugging step.
- Look up another code whenever a new one appears in a log.
Key Features
- Meanings for the standard HTTP status codes from 100 to 511.
- Plain-language explanations, not just the official reason phrase.
- Class identification for every code, including unlisted ones.
- Hints about the usual cause behind common error codes.
- Instant, free, and private with no sign-up.
Best Practices and Tips
- The first digit is the class: 1xx informational, 2xx success, 3xx redirection, 4xx client error, 5xx server error.
- A 301 is permanent and a 302 is temporary; search engines and browsers treat them very differently, so do not swap them casually.
- 401 means unauthenticated while 403 means authenticated but forbidden; the fix for each is completely different.
- A 502 from a proxy usually means the upstream server failed, not that your request was wrong.
- When an API returns an unfamiliar code, check the response body too; good APIs explain the error there.
Common Mistakes to Avoid
- Treating every 4xx as a user mistake; a 404 can equally mean a broken link or a missing route on the server.
- Assuming 500 means your code crashed; it means the server failed, which includes databases, upstreams, and configuration.
- Using 200 for errors and hiding the real problem in the body, which breaks caches, monitors, and clients.
- Confusing 301 and 308, or 302 and 307, which differ in whether the method may change on redirect.
Frequently Asked Questions
What do the five status classes mean?
1xx means the request was received and processing continues, 2xx means it succeeded, 3xx means further action such as following a redirect is needed, 4xx means the client made an error, and 5xx means the server failed to fulfil a valid-looking request. The first digit alone already tells you which side to investigate.
What is the difference between 401 and 403?
401 Unauthorized means the request lacks valid authentication, so logging in or supplying credentials may fix it. 403 Forbidden means the server understood the request and the credentials, but refuses to authorise it; logging in again will not help unless you log in as someone with permission.
Why do I see 301 and 308 for the same kind of redirect?
Both are permanent redirects, but 301 historically allowed changing a POST into a GET, while 308 strictly preserves the method and body. Modern APIs prefer 308 when the method matters, and 301 remains common for ordinary page moves.
What should I do about a 502 Bad Gateway?
A 502 means a proxy or gateway received an invalid response from the upstream server. Check whether the upstream service is running, whether it timed out, and whether the proxy configuration points at the right address, before changing your own request.
Are there status codes beyond the standard list?
Yes, servers sometimes use unassigned or custom codes, and this tool identifies their class from the first digit when it has no specific entry. The class alone is often enough to route the problem to the right team: client, server, or network.