HTTP 405 Method Not Allowed vs 426 Upgrade Required
Both HTTP 405 (Method Not Allowed) and 426 (Upgrade Required) belong to the 4xx Client Error category. 405 indicates that the HTTP method is not allowed for the requested resource. The response includes an Allow header listing valid methods. Meanwhile, 426 means that the server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
Description
The HTTP method is not allowed for the requested resource. The response includes an Allow header listing valid methods.
When You See It
When sending POST to a read-only endpoint, or DELETE to a non-deletable resource.
How to Fix
Check the Allow response header for supported methods. Use the correct HTTP method.
Description
The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
When You See It
When a server requires HTTPS or a newer protocol version.
How to Fix
Switch to the protocol specified in the Upgrade response header.
Key Differences
HTTP 405: The HTTP method is not allowed for the requested resource. The response includes an Allow header listing valid methods.
HTTP 426: The server refuses to perform the request using the current protocol but might after the client upgrades to a different protocol.
You encounter 405 when when sending POST to a read-only endpoint, or DELETE to a non-deletable resource.
You encounter 426 when when a server requires HTTPS or a newer protocol version.
When to Use Which
For 405 (Method Not Allowed): Check the Allow response header for supported methods. Use the correct HTTP method. For 426 (Upgrade Required): Switch to the protocol specified in the Upgrade response header.