501 Not Implemented
5xx Server error
The server does not implement that capability yet.
| On the wire | HTTP/1.1 501 Not Implemented |
|---|---|
| Code | 501 |
| 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 501 Not Implemented mean?
The server does not implement that capability yet.
Q. What does 501 Not Implemented look like on the wire?
It travels as HTTP/1.1 501 Not Implemented
Q. Is 501 Not Implemented an error?
Yes. A code starting with 4 blames the request; one starting with 5 blames the server.
Q. What group does 501 Not Implemented belong to?
The 5xx server error group; the rest of that group is listed further down.