Jetpack Compose (UI) is a powerful UI toolkit for Android. Have you ever wondered where this power comes from? The answer is Compose Runtime. In this talk, we will see how we can use Compose Runtime to create client libraries. Firstly, we will talk about Compose nodes, Composition, Recomposer, and how they are orchestrated to create a slot table. Then, we will see how the changes in the slot table are applied with an Applier. Moreover, we will touch upon the Snapshot system and how the changes in the state objects trigger a recomposition. Finally, we will create a basic UI toolkit for PowerPoint using Compose Runtime.