What are MCP resources and how do they differ from tools?

Resources in MCP servers allow you to expose data to clients, similar to GET request handlers in a typical HTTP server. They are perfect for scenarios where you need to fetch information rather than perform actions. Tools are about doing something, often with side effects, and Claude decides when to use them. Resources are about reading data, and your application code typically decides when to fetch them, often to inject context into a prompt or to populate a UI element like an autocomplete list. So you reach for tools when the model should act, and you reach for resources when your app needs data.