responsive-debugger.js

$(document).ready(function () {
  $debug = $('<div class="debug"></div>').css({
    position: 'fixed',
    bottom: 0,
    right: 0,
    color: "#fff",
    background: "#000",
    padding: "5px",
    "z-index": 99999
  }).appendTo('body');
  
  $(window).resize(function () {
   $debug.text($('body').width() + "x" + $('body').height());
  }).resize();
});