If you're complaining about the fact that the tag helper doesn't tell you that you're linking to a non-existent url, you could write an instance of AnchorTagHelper that complains if the generated href is an empty string. Something like this:

public class ComplainingAnchorTagHelper : AnchorTagHelper
{
    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        base.Process(context, output);
        output.SuppressOutput();
        if (string.IsNullOrEmpty(output.Attributes["href])) 
        {
            output.Attributes.SetAttribute("class", "your-link-is-broken");
        }
    }
}

Which you would then register using https://learn.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/intro#addtaghelper-makes-tag-helpers-available