Upgrade
Both directions
Proposes switching to another protocol; it pairs with a 101.
| On the wire | Upgrade: … |
|---|---|
| Category | Both directions |
Headers that can appear on either side.
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 Upgrade mean?
Proposes switching to another protocol; it pairs with a 101.
Q. What does Upgrade look like on the wire?
It travels as Upgrade: …
Q. Where does Upgrade appear?
In both directions.
Q. What group does Upgrade belong to?
The both directions group; the rest of that group is listed further down.