HTTP 400 – Bad Request

Common use case

Returned when a request body is malformed JSON, a required field is missing, or query parameters fail basic validation before any business logic runs.

Example

HTTP/1.1 400 Bad Request
Content-Type: application/json

{"error":"Missing required field: email"}

History

Part of the original HTTP/1.0 specification, RFC 1945 (1996).

Did you know?

It is the catch-all client error - APIs that don't distinguish between validation failures often lump many different problems under a single 400.