505 🌐 HTTP

HTTP 505 HTTP Version Not Supported

The server doesn’t support the HTTP protocol version used in the request.

Seen on: Linux

Meaning

Rare in browsers; usually caused by malformed request lines (spaces in the URL make the version part unparseable) or very old/new protocol versions between proxies and backends.

Common causes

  • Unencoded spaces in the URL break the request line (GET /my file HTTP/1.1)
  • Client forcing HTTP/2 or HTTP/3 to a backend that only speaks HTTP/1.x
  • Raw socket clients writing an invalid request line

⚡ Quick fix

  1. URL-encode the path (spaces → %20)
  2. Let the client negotiate the protocol instead of forcing it
  3. Check proxy → backend protocol settings

Detailed fix by platform

Linux

  1. Encode the URL:
    bash
    curl "https://example.com/files/annual%20report.pdf"

How to diagnose

  1. URL — Any spaces or control characters?
  2. Protocol — Which HTTP version does each hop use?

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