MCP Logging and Debugging

As we build more powerful MCP applications with multiple servers and complex tools, the ability to diagnose and understand what is happening under the hood becomes essential. In a distributed system with a client and one or more servers, simply running the code and hoping for the best is not a sustainable strategy. When things go wrong, we need a systematic way to find the root cause. When things go right, we need transparent logging and real-time insights to validate behavior and monitor system performance.

This lesson focuses on two fundamental practices that enable us to build reliable, production-ready agents. It is crucial to understand the distinction between them:

• Debugging: It is the reactive process of finding and fixing problems when an application is not working as expected. This often involves issues with the server’s configuration, its connection to the client, or its basic life cycle. We debug when the system is in a broken state.

• Logging: It is the proactive process of instrumenting the code to emit real-time, structured messages during a successful operation. This provides visibility into your tool’s internal logic, helps users understand the progress of long-running tasks, and creates an audit trail. We use logging to understand the behavior of a working system.

Mastering both of these skills is key to moving from simple prototypes to robust, maintainable AI applications. We will explore debugging techniques first, followed by implementing logging within our FastMCP tools.

Debugging server connections and configuration

Before we can see the logic of our tools, we need to ensure our server successfully connects to and communicates with the host client. When an MCP server fails to appear or respond in an application, the issue often lies not within our Python code but in the configuration that governs how the client launches and interacts with our server process.

Common failure points

When troubleshooting, it’s helpful to first check for the most common sources of error. These typically involve the server’s configuration within the host application. We should verify the following:

• Incorrect paths: The command and args in our configuration must point to the correct executable and script files using ...