Something like this:

my $type = Dict->of(
  foo => Str,
  baz => Optional[Int],
  qux => Optional[Str],
)->where(q{ exists $_->{baz} or exists $_->{qux} });

if ( $type->check( \%somehash ) ) {
  say "matched";
}
[download]

Also, might be worth looking into JSON-Schema-AsType.