Alt-Used
Request headers
Tells the server the client switched here because of Alt-Svc, which prevents loops.
| On the wire | Alt-Used: … |
|---|---|
| Category | Request headers |
Headers the browser attaches when it sends to the server.
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 Alt-Used mean?
Tells the server the client switched here because of Alt-Svc, which prevents loops.
Q. What does Alt-Used look like on the wire?
It travels as Alt-Used: …
Q. Where does Alt-Used appear?
In request headers.
Q. What group does Alt-Used belong to?
The request headers group; the rest of that group is listed further down.