This is a very simple WordPress plugin for a niche requirement. It sends a 404, page not found header to any visitors and displays a blank page instead of showing them your WordPress site.
The intent is for this to be used on a WordPress installation when you're using WordPress for content management but some other package, Laravel in my case, to actually display content.
What about previews?
The 404 headers are only sent to users that aren't logged in. Logged in users will see the WordPress site like normal so you'll be able to preview.