Currently the start page routing is handled by a HTTP module and cannot be skipped completely (but there's a workaround and a pending change).
What's possible to do as a workaround is to let your home controller inherit from PageController and to bypass the inherited action, like:
public class HomeController : PageController<StartPage> {
[NonAction]
public override ActionResult Index(StartPage currentPage) {
throw new NotImplementedException();
}
public ActionResult Index() {
return Content("Custom action");
}
}
However this isn't ideal, and in the major rewrite of the CMS (.NET Core compatibility etc) that is ongoing there have been a configuration option added to completely bypass the start page. This would be a small thing to add to the current version as well and I'm about to make a small beta release pretty soon where this could be included.