APIs are the backbone of modern web applications, but Rails controllers can get unwieldy when you try to support multiple versions, complex parameter validation, or JSON representations that change over time. The Grape gem offers a lightweight, Rack-based DSL for building RESTful APIs in a clean, object-oriented way. Pair it with the grape-entity plugin, and you get Ruby classes that encapsulate your JSON representation, keeping your controllers thin and your business logic organized.