What HTTP status response code should I use if the request is missing a required parameter?

Question

I am thinking 412 (Precondition Failed) but there may be a better standard?

Answer 1

You can send a 400 Bad Request code. It's one of the more general-purpose 4xx status codes, so you can use it to mean what you intend: the client is sending a request that's missing information/parameters that your application requires in order to process it correctly.