You can export for production the Gerbers and get a Gerber program to display it, I use KiCad GerbView. The export also has has a drill.txt file that you can open and check. The first group is drill sizes, and the succeeding groups are the batches of holes of the successive hole sizes. You can even use math on the X Y coordinates to check them.
I haven’t actually had anything made, but I assume the drill.txt is right.
There is an online Gerbviewer, but I don’t know how that works.