use JSON::PP;
use JSON::XS;
use JSON::Syck;

my $x = 123.1;
my $y = '123.10';
my $z = $y + 0;

my $h = { x => $x, y => $y, z => $z };

print JSON::PP::encode_json($h) . "\n";
print JSON::XS::encode_json($h) . "\n";
print JSON::Syck::Dump($h) . "\n";
__END__
{"y":"123.10","x":123.1,"z":123.1} #JSON::PP
{"y":"123.10","x":123.1,"z":123.1} #JSON::XS
{"y":123.10,"x":123.1,"z":123.1}   #JSON::Syck ( seems to do $y wrong/differently )