HTTP 101 Switching Protocols indicates the server understands and agrees to the client's request to change the application protocol via the Upgrade header. This is commonly seen during WebSocket handshakes where the connection upgrades from HTTP to the WebSocket protocol.
Status
101 Switching ProtocolsExample
GET /live-chat HTTP/1.1
Host: www.example.com
User-Agent: curl/8.6.0
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
Sec-WebSocket-Version: 13HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
<connection is now a WebSocket — messages flow both ways>How to Troubleshoot
Verify WebSocket handshake
If upgrading to WebSocket, confirm the server responds with Upgrade: websocket and Connection: Upgrade headers.
curl -v -H 'Upgrade: websocket' -H 'Connection: Upgrade' -H 'Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==' -H 'Sec-WebSocket-Version: 13' https://example.com/ws
Check proxy support
Ensure any reverse proxy (Nginx, Cloudflare) supports WebSocket pass-through. Proxies that do not forward Upgrade headers will break the handshake.
Common Causes
WebSocket connection upgrade
highThe client requested a WebSocket connection via the Upgrade: websocket header and the server accepted the protocol switch.
HTTP/2 upgrade from HTTP/1.1
mediumThe client requested an upgrade to HTTP/2 using the Upgrade header in an HTTP/1.1 request.
Quick Diagnostics
Related Status Codes
References
| Specification | Section |
|---|---|
| HTTP Semantics | RFC 9110 §15.2.2 |
Frequently Asked Questions
This reference was compiled from official RFCs, protocol specifications, and hands-on troubleshooting experience. AI tools were used primarily for formatting and organizing the content on the page.