What Is OP_CAT and Why Does It Matter?

Imagine building with LEGO blocks: you have two pieces and a connector that lets you join them to create something bigger. In Bitcoin script, OP_CAT works like that connector—it combines two pieces of data into one.

At first glance, OP_CAT may seem like a minor addition. However, allowing developers to combine data in scripts opens the door to creating more sophisticated proofs and logic within Bitcoin’s constraints. For example, suppose you need to prove that your name is on a guest list without revealing the entire list. With OP_CAT, you can merge just the necessary data to create a compact proof, showing only what’s needed.