As software systems grow increasingly complex, developers are often faced with the question: should a piece of functionality be built as a library or a service? While both options can fulfill the role of providing reusable functionality, each comes with distinct implications regarding maintainability, performance, and scalability. In this article, we’ll explore the critical differences, best practices, and key factors to help you decide the best approach for your project. This is a vital decision, as it impacts not only the architecture of your application but also its future evolution. By examining both options in detail, with comprehensive examples, you’ll be equipped to make an informed choice.