What does HTTP 101 mean?
The server agrees to switch to the protocol requested by the client in the Upgrade header.
Common causes and when you see it
Returned when upgrading a connection to WebSocket.
How to fix or handle it
If a WebSocket connection fails, check proxies and load balancers forward the Upgrade and Connection headers.
Test it yourself
Send a request with the online API tester, inspect the response with the HTTP header checker, or host an endpoint that returns 101 with the mock API generator to see how your app reacts.
HTTP 101 questions
The server agrees to switch to the protocol requested by the client in the Upgrade header.
Returned when upgrading a connection to WebSocket.
If a WebSocket connection fails, check proxies and load balancers forward the Upgrade and Connection headers.