HTTP 400 Bad Request vs 405 Method Not Allowed
Both HTTP 400 (Bad Request) and 405 (Method Not Allowed) belong to the 4xx Client Error category. 400 indicates that the server cannot process the request due to malformed syntax, invalid request message framing, or deceptive request routing. Meanwhile, 405 means that the HTTP method is not allowed for the requested resource. The response includes an Allow header listing valid methods.
Description
The server cannot process the request due to malformed syntax, invalid request message framing, or deceptive request routing.
When You See It
When sending malformed JSON, missing required fields, or invalid query parameters.
How to Fix
Check the request body format, validate all required fields, and ensure proper encoding.
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.
Key Differences
HTTP 400: The server cannot process the request due to malformed syntax, invalid request message framing, or deceptive request routing.
HTTP 405: The HTTP method is not allowed for the requested resource. The response includes an Allow header listing valid methods.
You encounter 400 when when sending malformed JSON, missing required fields, or invalid query parameters.
You encounter 405 when when sending POST to a read-only endpoint, or DELETE to a non-deletable resource.
When to Use Which
For 400 (Bad Request): Check the request body format, validate all required fields, and ensure proper encoding. For 405 (Method Not Allowed): Check the Allow response header for supported methods. Use the correct HTTP method.