HTTP headers
Upgrade HTTP Header Meaning
Upgrade asks to switch the connection to another protocol.
Meaning
The client or server is negotiating a protocol switch on the same connection.
Where it appears
WebSocket and HTTP protocol upgrades use it with Connection: Upgrade.
What to check
Check the 101 response, allowed protocols, and whether intermediaries forward upgrade headers correctly.
Example
Upgrade: websocketReferences
- Registry
- IANA HTTP Field Name Registry
- Guide
- MDN Upgrade