MCP Tools vs Resources vs Prompts: What to Expose to an AI Agent

When a team first wraps an internal platform in MCP, the result almost always looks the same: forty tools named get_x, list_x, create_x, and update_x, plus a few things that should never have been tools at all. The model gets lost, picks the wrong getter, and burns context reading giant responses it only needed a fragment of. The Model Context Protocol defines three root primitives — tools, resources, and prompts — because those are three genuinely different relationships an agent can have with your system. Mapping your capabilities onto them correctly is most of the design work. A tool is a f