using System;

using System.Linq;

using HtmlAgilityPack;

public class Program

{

    public static void Main()

    {

        var html = "<div>Some simple <p> html</div>";

        var htmlDoc = new HtmlDocument {

            OptionCheckSyntax = false

        };

        htmlDoc.LoadHtml(html);

​

        Console.WriteLine("error count: " + htmlDoc.ParseErrors.Count());

    }

}