MCPcat – A free open-source library for MCP server monitoring

In plain words

MCPcat is a free, MIT-licensed library that adds logging and observability to MCP servers with a single line of code. It captures tool calls, tracks user sessions, and provides context for agent actions, then pipes this data to monitoring vendors via OpenTelemetry. The library includes built-in support for Datadog and Sentry, making it easy for MCP server maintainers to implement drop-in observability without complex setup.

written from the facts on this page · September 2026

From the sources

In the maker’s words, at launch

Hey everyone! We've been working with several MCP server maintainers and we noticed some difficulties getting drop-in logging and identity attribution working out of the box with existing vendors. A couple of challenges we hoped to solve were: - Baseline piping of tool calls to traditional vendors - How to tie tool calls to a “user session” - Understanding the context behind tool calls made by agents So we built something. :) The MCPcat library is completely free to use, MIT licensed, and provides a one-line solution for adding logging and observability to any vendor that supports OpenTelemetry. We added custom support for Datadog and Sentry because we personally use those vendors, but we’re happy to add more if there’s interest. Here’s how it works: mcpcat.track(serverObject, {...options…}) This initializes a series of listeners that: 1. Categorize events within the same working session 2. Publish those events directly to your third-party data provider Optionally, you can redact sensitive data. The data never touches our servers (unless you opt in to additional contextual analysis, which I mention below). Some teams might also want a better understanding of “what use cases are people finding with my MCP server.” For that, we provide a separate dashboard that visualizes the user journey in more detail (free for a high baseline of monthly usage and always free for open source projects). We have two SDKs so far: Python SDK: <https:&#x2F;&#x2F;github.com&#x2F;MCPCat&#x2F;mcpcat-python-sdk> TypeScript SDK: <https:&#x2F;&#x2F;github.com&#x2F;MCPCat&#x2F;mcpcat-typescript-sdk> Other SDKs are on the way!

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