101 Switching Protocols
The server agrees to the protocol upgrade requested by the client via the Upgrade header. Most commonly seen when upgrading an HTTP connection to a WebSocket connection. The connection will no longer use HTTP after this response — the new protocol takes over.
What can I do?
- No action needed — this is an informational or success response, not an error.
How to debug & fix
- Verify your Upgrade and Connection: Upgrade headers are present and correctly spelled
- Ensure your reverse proxy (Nginx, Caddy) forwards the Upgrade header for WebSocket support
- Check that your server framework supports the target protocol
- Check that your reverse proxy (Nginx, HAProxy) correctly forwards the Connection: Upgrade and Upgrade headers.
- Test WebSocket connectivity with wscat: wscat -c wss://yourhost/ws
Code Example
// Node.js WebSocket upgrade
const { createServer } = require('http');
const server = createServer();
server.on('upgrade', (req, socket, head) => {
// Server sends 101 automatically on WebSocket upgrade
wss.handleUpgrade(req, socket, head, ws => {
wss.emit('connection', ws, req);
});
});Related Status Codes
How HTTP Status Codes Work
Every HTTP response carries a three-digit status code that tells the client — browser, API consumer, or search-engine crawler — exactly what happened. The first digit defines the class: 1xx informational (request in progress), 2xx success, 3xx redirection, 4xx client error (bad request, missing auth, not found), and 5xx server failure.
Status codes are standardised in RFC 9110 (HTTP Semantics, 2022). Extensions like WebDAV (RFC 4918) and rate-limit headers (RFC 6585) added codes beyond the core set. When a client receives an unrecognised code, the rule is to treat it as the generic x00 of its class.
Why the Right Code Matters
Semantically correct codes help search engines index accurately (301 passes link equity; 410 removes pages faster than 404), allow API clients to implement correct retry logic (429 + Retry-After, 503 + Retry-After), and let monitoring systems distinguish bugs (500) from load issues (503) from auth failures (401/403).
Looking up a different status code? The full reference covers all HTTP codes with causes, fix guides, and copyable code examples for Node.js and Python.
Browse the full HTTP Status Code reference →