505 HTTP Version Not Supported HTTP Status Code


HTTP Status Code 505, also known as "HTTP Version Not Supported," indicates that the server refuses to allow the HTTP protocol version that has been used in the request message. This error occurs when the HTTP version used in the request is known by the server but is not supported by it, or the server is unwilling to process requests with that version. For instance, if a client makes a request using HTTP/2.0, but the server only supports HTTP/1.1, the server might return a 505 error response.

This status code is part of the HTTP/1.1 standard, as defined in RFC 7231, and its purpose is to ensure that a web server can indicate to the client when a specific version of the HTTP protocol is not supported, suggesting indirectly that the client should try a different protocol version. When receiving a 505 error, the client may either downgrade the HTTP protocol version and retry the request or handle the error according to the application's requirements.


505 HTTP Version Not Supported

Common Causes

Here are the primary causes for a 505 HTTP Status Code:

  1. Unsupported HTTP Version: The most direct cause is that the HTTP version specified in the request is not supported by the server. For example, if the client sends a request using HTTP/2.0, but the server only supports versions 1.0 and 1.1, the server may respond with a 505 error.

  2. Configuration Issues: Server configuration might be set up to only allow specific versions of the HTTP protocol. If the request does not match these configurations, the server might respond with a 505 error.

  3. Reverse Proxy or Load Balancer Issues: In some cases, the issue might not be with the server itself but with a reverse proxy or a load balancer in front of the server. If these components are not configured to handle the version of HTTP presented by the client, they might return a 505 error.

  4. Security Concerns: Some servers may deliberately reject certain versions of the HTTP protocol due to known security vulnerabilities. For instance, older versions of the protocol may be less secure, prompting servers to accept only newer versions.

  5. Client Error: The issue might also stem from the client side, such as an outdated or misconfigured client attempting to use an HTTP version not widely supported.

  6. Networking or Communication Issues: In rare cases, network communication problems could lead to the corruption of request headers, including the HTTP version. This could cause the server to misinterpret the request and respond with a 505 error.

  7. Server Software Bugs or Limitations: Finally, software bugs or limitations in the server or web application could incorrectly handle or interpret HTTP protocol versions, leading to a 505 error response.

To resolve a 505 HTTP Status Code, it's often necessary to adjust the client request to use an HTTP version supported by the server, or to reconfigure the server or intermediate network components to support the desired HTTP version.

Browser Support

The following table will show you the current browser support for the 505 HTTP Version Not Supported HTTP status code.

Edge Chrome Firefox Opera Safari
Tablets / Mobile
Chrome Firefox Opera Safari Samsung Webview

Last updated by CSSPortal on: 1st April 2024