HTTP 505 HTTP Version Not Supported

What HTTP 505 means

Rare in practice. It can appear when a client sends a malformed request line, such as a URL with unencoded spaces, so the server misreads the version part.

How to fix a 505 error

• URL-encode spaces as %20 in request paths.

Retrying

Rarely. The server can’t handle this request, so retrying it unchanged is unlikely to help.

Example response

HTTP/1.1 505 HTTP Version Not Supported
Date: Wed, 21 Oct 2026 10:30:00 GMT
Content-Type: application/json

How to return 505

res.status(505).json({ error: 'HTTP Version Not Supported' });

from fastapi import HTTPException

raise HTTPException(status_code=505, detail="HTTP Version Not Supported")

http.Error(w, http.StatusText(http.StatusHTTPVersionNotSupported), http.StatusHTTPVersionNotSupported)

location /private/ {
    return 505;
}

Related status codes

• 400 Bad Request : The server can’t process the request because it is malformed.
• 426 Upgrade Required : The server refuses the request over the current protocol, and the client must upgrade.

Other 5xx status codes

500 Internal Server Error · 501 Not Implemented · 502 Bad Gateway · 503 Service Unavailable · 504 Gateway Timeout · 507 Insufficient Storage · 508 Loop Detected · 511 Network Authentication Required · 520 Web Server Returned an Unknown Error · 521 Web Server Is Down · 522 Connection Timed Out · 523 Origin Is Unreachable · 524 A Timeout Occurred · 525 SSL Handshake Failed · 526 Invalid SSL Certificate

See the full list of HTTP status codes.

Sources

• RFC 9110, section 505
• IANA HTTP Status Code Registry
• MDN: 505 HTTP Version Not Supported

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