MVC 4 client side validation not working

I had the same problem. It seems that the unobtrusive validation scripts were not loaded (see screenshot at the end). I fixed it by adding at the end of _Layout.cshtml

 @Scripts.Render("~/bundles/jqueryval")

The end result:

   @Scripts.Render("~/bundles/jquery")
   @Scripts.Render("~/bundles/jqueryval")
   @RenderSection("scripts", required: false)

Except for my pretty standard CRUD views everything is Visual studio project template defaults.

Loaded scripts after fixing the problem:

Be sure to add this command at the end of every view where you want the validations to be active.

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

I finally solved this issue by including the necessary scripts directly in my .cshtml file, in this order:

<script src="/Scripts/jquery.unobtrusive-ajax.js"></script>
<script src="/Scripts/jquery.validate.js"></script>
<script src="/Scripts/jquery.validate.unobtrusive.js"></script>

It's a bit off-topic, but I'm continually amazed by how often this sort of thing happens in Web programming, i.e. everything seems to be in place but some obscure tweak turns out to be necessary to get things going. Flimsy, flimsy, flimsy.

you may have already solved this, but I had some luck by changing the order of the jqueryval item in the BundleConfig with App_Start. The client-side validation would not work even on a fresh out-of-the-box MVC 4 internet solution. So I changed the default:

            bundles.Add(new ScriptBundle("~/bundles/jqueryval").Include(
                    "~/Scripts/jquery.unobtrusive*",
                    "~/Scripts/jquery.validate*"));

to

        bundles.Add(new ScriptBundle("~/bundles/jqueryval").Include(
                    "~/Scripts/jquery.validate*",
                    "~/Scripts/jquery.unobtrusive*"));

and now my client-side validation is working. You just want to make sure the unobtrusive file is at the end (so it's not intrusive, hah :)

In Global.asax.cs, Application_Start() method add:

DataAnnotationsModelValidatorProvider.RegisterAdapter(typeof(MyRequiredAttribute), typeof(RequiredAttributeAdapter));