1xx InformationalCommonly usedRFC 9110
101Switching Protocols
Server is switching to the protocol requested by the client.
What it means
The server agrees to switch protocols as requested by the client via the Upgrade header. Most commonly used when upgrading an HTTP connection to a WebSocket connection.
When to use it
- ✓Upgrading HTTP to WebSocket
- ✓Upgrading HTTP/1.1 to HTTP/2
- ✓Any protocol upgrade negotiation
Code Examples
WebSocket upgrade
javascript
const WebSocket = require('ws');
const wss = new WebSocket.Server({ port: 8080 });
// HTTP → WebSocket upgrade returns 101
wss.on('connection', (ws) => {
ws.on('message', (message) => {
ws.send(`Echo: ${message}`);
});
});Don't confuse with
Quick Facts
Code101
CategoryInformational
SpecRFC 9110
CommonYes
Relevant Headers
Upgrade
Specifies the protocol to switch to (e.g. websocket)
Connection
Must include "Upgrade"