An agent is the reasoning loop — it has an LLM that decides what to do, when, and why. MCP is just the protocol for exposing and calling tools — it has no intelligence and makes no decisions. MCP is the socket; the agent is the device plugged into it.

People conflate these because they're always used together, but they're different layers: an agent can exist without MCP, using hardcoded tool integrations, while MCP cannot exist without a client to drive it. In a typical flow, the agent reasons ("I need to query the DB"), the MCP client inside it sends tools/call to the right MCP server, the server executes and returns a result, and the agent observes that result and reasons again. MCP standardizes the last mile — how the agent reaches a tool — everything upstream of that, like planning, deciding which tool, and interpreting the result, is the agent's job, not the protocol's.