use Net::EmptyPort qw(check_port);

my $errors = validator($data)->(
  on      => '/ports/*',
  should  => sub { @_ > 0 },
  because => 'At least one port should be defined at "ports" section',
  each    => sub {
      my $port = $_->value;
      shift->report_error("The port $port is not available for usage")
          if(!check_port($port));
  }
)->errors;