#!/usr/bin/perl
use strict;
use CGI;
use JSON;
my $query = new CGI;
my $response = whatever(Query=>$query);
my $json = JSON->new->utf8(1)->pretty(1)->allow_nonref->encode($response);
print $query->header('application/json').$json;

sub whatever {

    # Here you can do REALLY anything, and send back an hash reference
}