MCP Life Cycle and Communication Protocol

The conversation between an AI application (the client) and an external tool (the server) follows a formal process to ensure reliability. This process governs how the connection starts, what happens during the interaction, and how it ends cleanly. This is the MCP life cycle.

Think of the life cycle as the official etiquette for this conversation. This structured process ensures that communication is predictable, reliable, and efficient from start to finish. The entire life cycle consists of three distinct phases. Let’s go over each, in detail.

Phase 1: Initialization (The handshake)

Before any real work can be done, the client and server must formally introduce themselves and agree on the rules of engagement. This is the “handshake” phase.

• The client calls first: The connection always starts with the client sending an initialize request to the server. This message is akin to saying, “Hello, I’m an AI application, and here are my capabilities and the protocol versions I can speak.”

• The server responds: The server receives this request, replies with its own capabilities, and confirms the protocol version.

• The client sends the notification to confirm initialization.

This initial exchange is critical. It ensures that both the client and server are compatible and aware of what the other can do before the main conversation begins. It also prevents errors that might arise if, for example, the client tries to use a feature the server doesn’t support.

Once the handshake is complete, the connection is officially open, and we move into the operation phase.

Phase 2: Operation (The conversation)

This is where the real work happens. With the connection established, the client and server can now exchange messages freely according to the rules they agreed upon during initialization.

• The client can send requests to the server to use its tools or access ...