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All HTTP status codes
1xx Informational
RFC 9110

101 Switching Protocols

The server agrees to switch protocols as requested by the client via the Upgrade header.

What it means

HTTP 101 indicates that the server understands and is willing to comply with the client's request, via the Upgrade header field, for a change in the application protocol being used on this connection.

When it's used

Most commonly seen when upgrading an HTTP connection to WebSocket, or when negotiating HTTP/2 over an HTTP/1.1 connection.

Common causes
  • WebSocket handshake initiated
  • HTTP/2 upgrade requested via Upgrade: h2c
  • TLS upgrade via Upgrade: TLS/1.2
How to fix it
  • Not an error — confirms protocol upgrade succeeded
  • If unexpected, check whether your client library is requesting an Upgrade header
  • Verify the new protocol handler is correctly initialized after the switch
Example response
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
SEO impact

Not relevant to crawlers in standard HTML contexts.