Earlier this week, I read a post titled “Build Libraries, Not Apps“, where the author (Nicolás Ortega Froysa) puts forth an idea that software developers should create the main part of their applications as libraries, then create APIs so that other developers can create alternate user interfaces in other clients if desired. I can see that being an appealing goal for developers who want their application to be used in lots of other settings. However, I do not think that most applications are designed to have alternate user interfaces. For myself, I think of the user interface that I want my application to have, and then create it, and then create the logic that powers that interface. It is not a design goal for me to support an API. Froysa mentions different ways that Unix/Linux applications can interact with libraries (GUI, text interface, command line interface). To me, if a design goal of the application is to support multiple clients, or provide services to other applications, then including an API makes sense.