If you want to use ASP.NET’s ValidationSummary, you have two options: display a div inline with the summary of the validation errors, or display an ugly alert() box.

There are a couple of guides which explain how to make ValidationSummary display the errors in a modal of your choice, but all are annoyingly incomplete. One even required you to change the ASP.NET core files, which is a hassle if you ask me.

I’m going to take a different, easier path.

Since ValidationSummary uses alert, I’ll replace alert with the modal of my choice.

function alert(msg) {   mymodal(msg); }

Now all you have to do is find a nice modal box.