Getting over all code coverage using Tooling API

ToolingAPI.html

<apex:page showHeader="true" sidebar="true" docType="html-5.0"  standardStylesheets="false">
  <script src="//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js"></script>
 
  <script>
    $(document).ready(function(){
      $.ajax('/services/data/v30.0/tooling/query/?q=SELECT PercentCovered FROM ApexOrgWideCoverage',
        {
          beforeSend: function(xhr) {
            xhr.setRequestHeader('Authorization', 'Bearer {!$Api.Session_ID}');
          },
          success: function(response) {
            var overall;
            $.each(response.records, function(index, record) {
               $('#percen').append(record.PercentCovered);
            });
          },
          error: function(jqXHR, textStatus, errorThrown) {
             alert(jqXHR.status + ': ' + errorThrown);
          }
        }
      );
    });
  </script>
  
  <p id="percen">Over all code coverage: </p>
  
</apex:page>