HTTP 505 HTTP Version Not Supported means the server does not support the major HTTP protocol version used in the request. For example, the client sent an HTTP/2 request to a server that only supports HTTP/1.1.
Status
505 HTTP Version Not SupportedExample
Request
GET / HTTP/0.9
Host: www.example.com
User-Agent: Mozilla/5.0
Accept: text/htmlResponse
HTTP/1.1 505 HTTP Version Not Supported
Content-Type: text/html; charset=utf-8
Content-Length: 181
<!doctype html>
<html lang="en">
<head>
<title>505 HTTP Version Not Supported</title>
</head>
<body>
<h1>HTTP Version Not Supported</h1>
<p>The server does not support the HTTP version used in this request.</p>
</body>
</html>How to Troubleshoot
1
Use a supported HTTP version
Try the request with HTTP/1.1.
curl --http1.1 https://example.com/
2
Update the server
Upgrade the web server software to support modern HTTP versions.
Common Causes
Unsupported HTTP version
highThe client is using a newer HTTP version than the server supports.
Related Status Codes
References
| Specification | Section |
|---|---|
| HTTP Semantics | RFC 9110 §15.6.6 |
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.