When you place a furnace, smoker, blast furnace, brewing stand, jukebox, or beehive, then item display entities will appear showing you what is inside those blocks. If you set down a campfire, then you can see how long until your food is cooked with the help of a text display entity.

The block with the GUI you want to peep into must have "free space" above it, like (air, water, or a trapdoor) above it.
Brewing stand particles! Since many potions look alike, I made them display particles to distinguish them:
* All potions produce the effect particles of their own color.
* Extended potions produce redstone dust particles.
* Potions strengthened with glowstone dust produce yellow dust particles.
* Awkward potions produce nether wart block particles.
* Thick potions produce glowstone block particles.
* Mundane potions produce cyan terracotta particles.
Happy peeping!

