Is it possible to debug Global.asax?

A simple way to break in Application_Start() is to use the System.Diagnostics.Debugger class. You can force the application to break by inserting System.Diagnostics.Debugger.Break() where you would like the debugger to break.

void Application_Start(object sender, EventArgs e) 
{
     System.Diagnostics.Debugger.Break();

     // ...
}