I\'m a huge fan of asp.net 4.5 webforms model binding using data annotations.
ascx:
Guys webforms have complete client side validation, it just needs to be specified once in the model, that's the whole point of Model Binding and DataAnnotations check these links below.
In short Add the following reference to your Model class library project.
using System.ComponentModel.DataAnnotations;
Add this line to your web.config
Follow this link for details Webforms Model Validation
And this link for Microsoft's complete documentation Microsoft documentaion