HTTP Status Codes
HTTP 505 HTTP Version Not Supported
HTTP Version Not Supported
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.
Visual summary
A quick reference view of how HTTP 505 works: A mismatch in communication standards between client and server.
What 505 Means
The shortest useful reading of this status code.
HTTP Version Not Supported.
This status falls into the 5xx class, indicating a server-side error outcome for the request.
Quick read
HTTP Version Not Supported
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 Context
How this status behaves without turning the page into a repair guide.
Standard usage
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.
Technical nuance
This helps server administrators forcefully phase out insecure or globally outdated transport methods.
Related HTTP Codes
Nearby HTTP status codes help clarify how 505 differs inside the same response family.
505
HTTP Version Not Supported
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.
500
Internal Server Error
the server hit an unexpected condition while handling the request
501
Not Implemented
the server does not support the HTTP method used in the request
400
Bad Request
the server cannot process the request because it is malformed
Common Causes
Client requesting extremely old HTTP/0.9
A common condition that triggers a 505 response when the web server evaluates the transaction.
Client forcing unconfigured HTTP/3 or HTTP/2
A common condition that triggers a 505 response when the web server evaluates the transaction.
Malformed HTTP version string in request
A common condition that triggers a 505 response when the web server evaluates the transaction.
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
Ensuring the HTTP client or library utilizes a modern protocol version like HTTP/1.1 or HTTP/2 resolves the version mismatch.
Frequently Asked Questions
Common interpretation questions about HTTP 505.
Updating the client library to use HTTP/1.1 or configuring the web server to permit legacy protocols resolves the version mismatch.