flask-restful has a useful request parser with which one can declare required and optional arguments in various request locations such as the query string or in json content. Arguments that are not declared are ignored by the parser.
Is there a way to restrict the arguments, so that if a request contains undecalred arguments the server would respond with a 500 Bad Request instead of ignoring them?
Yup, if you check out the docs then you'll see that you can pass a strict=True parameter to parse_args(), which will do what you want.