HTTP Version Not Supported
What 505 Means
The 505 error on the HTTP Status-Codes indicates http version not supported. This typically occurs due to client requesting extremely old http/0.9.
A 505 error occurs when the server actively refuses to support the major version of the HTTP protocol that was used in the client's request message.
Technical Background
Modern web servers enforce protocol policies. If a server is configured to strictly only talk HTTP/1.1 or HTTP/2, dropping HTTP/1.0 traffic results in a 505.
This helps server administrators forcefully phase out insecure or globally outdated transport methods.
Common Causes
- Client requesting extremely old HTTP/0.9
- Client forcing unconfigured HTTP/3 or HTTP/2
- Malformed HTTP version string in request
Typical Scenarios
- An IoT device utilizes an ancient HTTP/1.0 protocol that a modern Nginx host has completely disabled.
- Malformed proxy software accidentally mangles the HTTP declaration string.
What to Know
Ensure your HTTP client or web scraping library is utilizing a modern, widely accepted protocol version like HTTP/1.1 or HTTP/2.
Frequently Asked Questions
Common questions about HTTP 505 error
Update your client library to use HTTP/1.1 or configure your web server to backward-allow older protocols if required.