Recently I've been using more and more Vue.js in the client code for my ASP.NET MVC websites. It provides a great balance between modern interactive client functionality and server logic. However, one area that's been troubling me is how to integrate the powerful built-in ModelState server-side validation framework with the client, particularly in WebAPI or other service-based scenarios. Ideally, I'd like to display server-side validation errors on the client when data fails to validate due to validation attributes like [Required]. This article shows one way to do that.