Skeleton Key in The Binding of Isaac is a passive item that instantly sets your key count to 99, so you use it by picking it up and then spending keys normally like always. It also leaves you with a keyhole on Isaac’s forehead as a visual effect.

What it actually does

  • Gives you 99 keys right away.
  • The 99-key cap stays even if you reroll the item.
  • It’s especially strong if you plan to open lots of chests, doors, or key-based rooms over the rest of the run.

Best way to use it

  • Spend any keys you already have before picking it up, so you don’t waste part of the effect.
  • After grabbing it, use keys freely on item rooms, shop doors, and special locks as normal.
  • If you have a Bombs Are Key pill, it can convert that key stockpile into bombs instead.

Simple takeaway

Think of Skeleton Key as a huge key refill: pick it up, then enjoy near- unlimited key spending for the rest of the run.

TL;DR: It gives you 99 keys. Pick it up, then use keys normally; it’s best to spend your current keys first so you don’t overcap.