Normally, when you used HttpPost/Form submission to post the view through the controller then you can have the model validation applied automatically through @Html.ValidationSummary()

But how do you get the ModelState errors through Json? You can still use LINQ to get the model errors from the ModelState and pass it through JSON

Code Snippet
  1. public ActionResult JsonRegister(MemberModel.RegistrationModel model)
  2.         {
  3.             string error = string.Empty;
  5.             if (!ModelState.IsValid)
  6.             {
  7.                 IEnumerable<System.Web.Mvc.ModelError> modelerrors = ModelState.SelectMany(x => x.Value.Errors);
  8.                 foreach (var modelerror in modelerrors)
  9.                 {
  10.                     error += modelerror.ErrorMessage + “\n”;
  11.                 }
  12.             }
  13.             return Json(new { success = false, errors = error }, JsonRequestBehavior.AllowGet);
  14.         }