All HTTP status codes

HTTP 101 Switching Protocols

Informational

The server agrees to switch to the protocol the client requested in the Upgrade header — most commonly seen when establishing a WebSocket connection.

Defined in RFC 9110

Common causes

  • WebSocket handshake (Upgrade: websocket)
  • HTTP/1.1 to HTTP/2 cleartext upgrade (h2c)

How to fix it

  1. Nothing to fix on success

  2. If the upgrade fails instead, verify the proxy/load balancer forwards Upgrade and Connection headers

Related status codes

100 Continue

The server received the request headers and the client should proceed to send the request body. Used with the Expect: 100-continue header on large uploads.

426 Upgrade Required

The server refuses to serve the request over the current protocol; the Upgrade header says which protocol to switch to.

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