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Guide
About the HTTP Status Code Reference
Every HTTP response carries a three-digit status code that tells the client what happened. The first digit sets the category — 2xx means success, 3xx a redirect, 4xx a client mistake, and 5xx a server failure. Knowing them makes debugging APIs and websites far faster: the code usually points straight at whether the problem is your request or the server.
This reference lists the codes you'll actually encounter, with plain-language explanations. Search by number or name, or filter by category.
The five classes at a glance
- 1xx Informational — the request was received and processing continues.
- 2xx Success — the request was received, understood, and accepted.
- 3xx Redirection — further action is needed, usually following a new URL.
- 4xx Client Error — the request was wrong (bad data, missing auth, not found).
- 5xx Server Error — the request was valid but the server failed to handle it.
Codes people mix up
401 vs 403: 401 means you're not authenticated (log in), while 403 means you're authenticated but not allowed. 301 vs 302: 301 is a permanent move (search engines update their links), 302 is temporary (keep using the original URL). 502 vs 504: 502 means a proxy got a bad response upstream, 504 means the upstream didn't respond in time.
How to use it
- 1Search for a code or name, like "404" or "forbidden".
- 2Or filter by class (2xx, 4xx, 5xx) to browse a category.
- 3Read the plain-language description to understand the cause.
- 4Use it to decide whether the fix is on the client or the server.
Frequently asked questions
What is the difference between 401 and 403?
401 Unauthorized means you are not authenticated — you need to log in or provide valid credentials. 403 Forbidden means you are authenticated but lack permission for that resource.
When should I use 301 vs 302?
Use 301 Moved Permanently when a URL has changed for good, so search engines update their index. Use 302 Found (or 307) for a temporary redirect where the original URL should still be used later.
What does a 500 error mean?
500 Internal Server Error is a generic message that the server hit an unexpected condition. The real cause is in the server logs, not the status code itself.
What status code should a successful API POST return?
Commonly 201 Created when a new resource is made, or 200 OK if it returns a result, or 204 No Content if there is nothing to return.
What is 429 Too Many Requests?
It means you have hit a rate limit. Slow down and check for a Retry-After header indicating when you can try again.