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400 4xx RFC 9110 §15.5.1

Bad Request

Server cannot process the request due to malformed syntax, invalid parameters, or invalid state.

What HTTP 400 means

RFC 9110 §15.5.1. The catch-all 4xx for client-side errors that don't fit a more specific code. Common causes: malformed JSON, missing required fields, invalid query parameters, request body too large for the parser, invalid Content-Type.

Typical causes

  • Malformed JSON body
  • Missing required parameters
  • Invalid Content-Type
  • Field validation failure
  • Schema mismatch

400 across services

How 3 different errors map to HTTP 400 across the services we cover.

AWS

OpenAI

Stripe