That's how I'd do it.

Purely out of esthetical reasons

use strict;
use warnings;

print "-------\n";
print json_here();
print "-------\n";


sub chompit {
    my $str = shift;
    chomp $str;
    return $str;
}


sub json_here {
    chompit << '__JSON__' ;
      "Type": 0,
      "Width": 504,
      "X": 18,
      "Y": 18
    }
  ]
}
__JSON__
}
[download]

update

changed END_JSON to __JSON__

• I like naming the HERE-ID after the format, that's a plus and can help the IDE with formatting
• But I don't wanna read END_ at the start
• Surrounding underscores are a (my?) visual anchor to recognize a here doc