510 Not Extended
5xx Server error
The request needs a further extension to be fulfilled.
| On the wire | HTTP/1.1 510 Not Extended |
|---|---|
| Code | 510 |
| Is it an error | Yes — this is an error |
| Category | 5xx Server error |
The problem is on the server side; retrying later is often worth it.
How to read this
- The first digit of a status code carries the meaning: 4 means the request, 5 means the server.
- 404 means "not there"; 403 means "there, but not for you". Swapping them makes debugging slower.
- Header names are case-insensitive — Content-Type and content-type are the same header.
- Caching and CORS problems usually come down to one header line, visible in the browser’s network tab.
Frequently asked questions
Q. What does HTTP 510 Not Extended mean?
The request needs a further extension to be fulfilled.
Q. What does 510 Not Extended look like on the wire?
It travels as HTTP/1.1 510 Not Extended
Q. Is 510 Not Extended an error?
Yes. A code starting with 4 blames the request; one starting with 5 blames the server.
Q. What group does 510 Not Extended belong to?
The 5xx server error group; the rest of that group is listed further down.