How do you choose between tools, resources, and prompts in MCP?

Here is a quick decision guide. Need to give Claude new capabilities the model can choose to use on its own? Use tools. Need to get data into your app for UI elements or to add context to a prompt? Use resources. Want to create predefined workflows that users trigger on demand? Use prompts. You can see all three primitives in action in Claude's official interface. The workflow buttons demonstrate prompts. The Google Drive integration shows resources in action. And when Claude executes code or performs calculations, it is using tools behind the scenes. Each primitive serves a different part of your application stack.