HTTP 426 Upgrade Required means the server refuses to perform the request using the current protocol but will accept it after the client upgrades to a different protocol. The response includes an Upgrade header indicating the required protocol.
Status
426 Upgrade RequiredExample
GET /account HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/htmlHTTP/1.1 426 Upgrade Required
Upgrade: TLS/1.2, HTTP/1.1
Connection: Upgrade
Content-Type: text/html; charset=utf-8
<!doctype html>
<html>
<body>
<h1>426 Upgrade Required</h1>
<p>Please use HTTPS to access this page.</p>
</body>
</html>How to Troubleshoot
Check the Upgrade header
The response includes an Upgrade header specifying the required protocol.
Switch to the required protocol
Use HTTPS instead of HTTP, or initiate a WebSocket connection if that is what the server requires.
Common Causes
HTTPS required
highThe server requires an encrypted connection and the client is using plain HTTP.
WebSocket upgrade required
mediumThe endpoint only accepts WebSocket connections but received a standard HTTP request.
Related Status Codes
References
| Specification | Section |
|---|---|
| HTTP Semantics | RFC 9110 §15.5.22 |
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.