← All status codes4xx – Client Error

HTTP 426 – Upgrade Required

The server refuses to perform the request using the current protocol and wants an upgrade.

Common use case

Used to force clients from plain HTTP onto a newer protocol, e.g. requiring TLS or HTTP/2 before continuing.

Example

HTTP/1.1 426 Upgrade Required
Upgrade: TLS/1.2, HTTP/1.1

History

Part of RFC 2817 (2000), which defined the Upgrade mechanism for negotiating TLS over an existing HTTP connection.

Did you know?

It is the mirror image of 101 Switching Protocols - 101 says "ok, switching now", while 426 says "you must switch before I'll continue".

Other 4xx codes

400Bad Request401Unauthorized402Payment Required403Forbidden404Not Found405Method Not Allowed406Not Acceptable407Proxy Authentication Required408Request Timeout409Conflict410Gone411Length Required412Precondition Failed413Content Too Large414URI Too Long415Unsupported Media Type416Range Not Satisfiable417Expectation Failed418I'm a teapot422Unprocessable Content425Too Early428Precondition Required429Too Many Requests430Shopify Security Rejection431Request Header Fields Too Large444No Response451Unavailable For Legal Reasons460Client Closed Connection463Malformed X-Forwarded-For Header464Incompatible Protocol Versions494Request Header Too Large495SSL Certificate Error496SSL Certificate Required497HTTP Request Sent To HTTPS Port499Client Closed Request