The operational difference MCP introduces is not cosmetic. Before a shared protocol, agents interacted with external systems through natural-language instructions — prompts engineered to coax a model into calling the right function in the right way. That approach is brittle: it fails when prompt formatting shifts, when models update, when tool APIs change. MCP replaces that brittleness with a typed interface [5]: the agent declares what tool it needs, passes structured arguments, and receives structured output. The handshake is machine-readable in both directions.