All HTTP status codes

HTTP 426 Upgrade Required

Client Error

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

Defined in RFC 9110

Common causes

  • Endpoints that require switching protocols (e.g. to TLS or HTTP/2)

How to fix it

  1. Reconnect using the protocol named in the Upgrade header

Related status codes

101 Switching Protocols

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

505 HTTP Version Not Supported

The server doesn't support the HTTP protocol version used in the request.

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