Agent systems usually need two kinds of interoperability.

The first is tool interoperability: how an AI application connects to tools, data, prompts, and resources. That is what MCP (Model Context Protocol) is for.

The second is agent interoperability: how one agent delegates work to another agent and follows that work over time. That is what A2A (Agent2Agent Protocol) is for.

They are often mentioned together because they both help agent systems connect to things outside themselves. But they solve different problems.

The boundary matters. If you treat every remote system as a simple tool, you lose the idea of a task with progress, clarification, and a lifecycle. If you wrap every small function as an agent, you add latency and operational complexity without gaining much.