TheBounding Block Outline Mod is a mod for Minecraft that outlines structures generated by the game itself. This is useful because it can tell you if a structure is genuine or just created by another player, but more importantly, can tell you if a wither skeleton or witch will spawn there.
Before this mod, a person could easily fool you by creating a fake witch hut. On top of that, that Nether fortress you found could end up being a structure that doesn’t even allow for wither skeletons to spawn. That would ultimately lead to a waste of time. Thanks to this mod, you can now find out if that structure will spawn rare mobs, just by looking to see if it has an outline, all without having to give up your precious time. All you have to do is press “F3″ and the “N” button at the same time to enable the overlay.
All in all, this mod is a great mod for everyone. I would definitely recommend this mod to any survival player that would like to know if the structure they encountered is a spawning structure. Now for some screenshots of the mod.