Handling Connection Lifecycles

Managing the connection between an MCP client and a server involves more than just sending prompts. Unlike a standard REST API where requests are often isolated and stateless, an MCP connection represents a persistent session. The client, whether it is the Claude Desktop app or a custom implementation, must spawn the server process, negotiate capabilities, maintain the communication channel, and handle termination gracefully. Failing to manage this lifecycle results in zombie processes, corrupted JSON-RPC streams, and unresponsive interfaces.

The Initialization Handshake

The lifecycle begins immediately after the client executes the server binary. Before any resources or tools can be exchanged, the client and server must agree on the protocol version and their respective capabilities. This negotiation happens through a strict initialization sequence defined by the MCP specification.

When the server process starts, it listens for an initialize request. The client sends this request containing the protocol version it supports and a set of capabilities (such as whether it supports sampling or roots). The server processes this message and responds with its own capabilities, declaring which resources, prompts, or tools it provides.

The handshake concludes only when the client sends an initialized notification. Until this three-step sequence is complete, the server rejects all other requests.

The initialization sequence establishes the contract between client and server. The server cannot send resource updates until it receives the final initialized notification.

Transport Stability and Standard IO

In the default configuration for local development, MCP uses Standard Input and Output (Stdio) as the transport layer. This architecture places specific constraints on how you write server code. Because stdout is reserved exclusively for JSON-RPC messages, any stray output, such as a print() statement used for debugging, will corrupt the message stream. The client will fail to parse the JSON and likely terminate the connection.

To maintain a stable lifecycle, you must ensure that all logging is directed to stderr. The official Python and TypeScript SDKs handle this automatically when configured correctly, but direct writes to standard output must be avoided.

The client also acts as the process manager. It holds the handle to the server's process ID (PID). If the client crashes or is closed, the operating system closes the pipes connected to the server's stdin and stdout. A server implementation detects this closure (End of File or EOF) and terminates itself immediately to prevent resource leaks.

Heartbeats and Health Checks

Once the connection is established, the client and server may sit idle for long periods. To ensure the connection remains active and the server process hasn't hung, the protocol supports a ping method.

Clients can periodically send a JSON-RPC ping request. The server must respond with an empty result. If the server fails to respond within a timeout window, the client assumes the connection is dead and initiates the termination procedure. This mechanism is critical for long-running sessions where network interruptions (in the case of SSE) or process scheduler pauses might occur.

Graceful Termination

The end of a connection is as critical as the beginning. A forceful termination (sending a SIGKILL) can leave database locks open or temporary files on the disk. The MCP specification allows for a graceful shutdown sequence.

Ideally, the client sends a notification or closes the input stream, signaling the server to shut down. In Python using asyncio, this often triggers a CancelledError within the server's main event loop. Your server code should catch this signal or use context managers (async with) to perform cleanup tasks.

Common cleanup tasks include:

• Closing database connections.
• Unsubscribing from external webhooks.
• Deleting temporary cache files.

The following diagram illustrates the states a server transitions through during a typical session.

Valid server states flow from process creation to active capability exchange and finally to cleanup. The dashed line represents an unrecoverable error state that bypasses cleanup.

Error Recovery Strategies

Despite lifecycle management, errors occur. If a server crashes, the client must decide whether to restart it. Most clients, including Claude Desktop, employ a backoff strategy. They may attempt to restart the server immediately, but if it crashes repeatedly on startup (a "crash loop"), the client will disable the server to protect the system stability.

When developing servers, you can influence this behavior by using appropriate exit codes. Exiting with code 0 usually indicates a deliberate shutdown, while non-zero codes indicate errors. However, the most effective recovery strategy is preventing the crash entirely by wrapping top-level tool execution logic in try/except blocks. This allows the server to return a JSON-RPC error response to the specific request while keeping the main process and connection alive.

By understanding these states, Initialization, Active Communication, and Termination, you ensure your MCP server acts as a reliable component in the larger AI ecosystem, rather than a fragile script that requires constant manual restarts.