Custom ajax "unique" validator with reason in response

validate.js

var validator = $('form').validate({
  rules: {
    number: {
      remote: {
        url: 'UniqueNumber',
        dataType: 'json',
        success: function(data) {
          if (data.unique == true) {
            return;
          }

          validator.showErrors({ number: 'Not unique because of ' + data.reason });
        }
      }
    }
  }
});