HTTP Status Lookup
Search every HTTP status code with a plain-English explanation of when to use it.
Every HTTP Status Code, Explained
Status codes carry the whole conversation between client and server, and most of the confusion around them is about pairs that look interchangeable and are not. 301 against 302 determines whether search engines transfer ranking. 401 against 403 is the difference between "who are you" and "not you". 502 against 504 points at completely different failures in your infrastructure.
This reference covers every code with what it means, when to send it, and what usually causes it when you receive one unexpectedly. Search by number or by description.
Key features
- Every code that matters — the registered responses from 100 to 511, each with a plain-English line on what it actually means.
- Search by number or meaning — type 404, or type "not found", or type "redirect", and the list narrows as you type.
- Filter by class — 2xx, 3xx, 4xx or 5xx in one tap, for when you know roughly where the answer lives.
- Class shown on every row — informational, success, redirect, client error or server error, so the shape of the response is never in doubt.
- No lookup round trip — the whole table is in the page, so it answers instantly and works offline.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: HTTP Status Lookup
- Search for the code
Enter a number, or describe what you are trying to express. - Read the explanation
One line on what the code means and what it implies for the client. - Filter by class
Narrow to 2xx, 3xx, 4xx or 5xx when you know the family but not the number. - Scan the neighbours
Related codes sit next to each other, which often surfaces a better fit than the one you came for.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Developer |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
What is the difference between 301 and 302?
301 is permanent: clients cache it, and search engines transfer ranking signals to the new URL. 302 is temporary: nothing is transferred and the original stays canonical. Using 302 for a permanent move is a common and costly SEO mistake.
When should I use 401 versus 403?
401 means you have not authenticated, or your credentials were not accepted — retrying with valid credentials may work. 403 means you are authenticated and still not permitted; retrying will not help. 401 must include a WWW-Authenticate header.
What causes a 502 or 504?
502 means a gateway received an invalid response from upstream — typically the application crashed or returned garbage. 504 means upstream did not respond in time — typically it is overloaded or stuck. The distinction tells you where to look.
Should an API return 200 with an error in the body?
No. It defeats every layer of tooling that reads status codes — monitoring, retry logic, caches and client libraries all rely on them. Use the correct status and put the detail in the body.