Client Error (4xx)
HTTP 426 — 426 Upgrade Required
The client should switch to a different protocol such as TLS/1.3 or WebSocket specified in the Upgrade header.
Common Causes & Diagnoses
- •Connecting with plaintext HTTP to an endpoint requiring modern TLS or WebSocket handshake.
Spesifikasyon & Kategori
Status Code:426
Category:Client Error (4xx)
RFC Standard:RFC 9110 / HTTP/1.1 & HTTP/2
Multi-Language Code Implementations
How to Handle, Return & Test HTTP 426
Status: 426 426 Upgrade Required
server.js / handler.ts
// Express.js Server Response
app.get('/api/resource', (req, res) => {
// Returning 426 426 Upgrade Required
return res.status(426).json({
error: '426 Upgrade Required',
statusCode: 426,
timestamp: new Date().toISOString()
});
});
// Client-side fetch error check
const response = await fetch('/api/resource');
if (response.status === 426) {
console.warn('Received HTTP 426 426 Upgrade Required');
}💡 Pro Tip: Ensure appropriate error handling middleware or proxy interceptors are enabled so client applications receive structured JSON responses for HTTP 426.
How to Fix / Practical Code Solutions
Send Upgrade Header
Ensure client sends Upgrade: websocket and Connection: Upgrade headers during handshake.
Other Popular HTTP Status Codes
Frequently Asked Questions
Common Questions About HTTP 426 to RFC Standard
Everything you need to know regarding specifications, syntax, and security best practices.
The client should switch to a different protocol such as TLS/1.3 or WebSocket specified in the Upgrade header. In Turkish: İstemcinin Upgrade başlığında belirtilen protokole (ör. WebSocket veya TLS) geçmesi zorunludur.