introspect_mutations

{
  __schema {
    mutationType{
      fields {
        name 
        args{
          name 
          type {
            ...TypeDesc
          }
        }
      }
    }
  }
}

fragment TypeDesc on __Type {
  name
  kind
  ofType {
    name
    kind
    ofType {
      name
      kind
      ofType {
        name
        kind
      }
    }
  }
}