What makes a good API for a library? Or more importantly, what makes it bad? Implementing an API is an art. It’s the connection between the user and the library itself. How can we optimize that connection to make the experience more pleasing? What makes a user reach for one library over another? What goes into an ergonomic API? This talk will first discuss what makes an API good: documentation, simplicity, consistency, completeness, and flexibility. We will apply those elements by looking at developing and iterating on our own library.