Minimal MCP in Nix

Minimal MCP in Nix – A Lightweight, Declarative MCP Server

The Minimal MCP in Nix server solves a common pain point for developers who want to expose simple, reproducible tools to Claude or other AI assistants without the overhead of managing a full‑blown service. By packaging the MCP implementation in Nix, the server guarantees deterministic builds and zero‑configuration deployments across any system that supports Nix. This eliminates version drift, dependency conflicts, and the need to manually install Python or its libraries—an attractive proposition for teams that already rely on Nix for package management.

At its core, the server offers two straightforward capabilities: a stub location endpoint and a time‑retrieval tool. The stub simply returns the URL where the demo is currently hosted, allowing developers to verify that the MCP endpoint is reachable and correctly registered in their Claude configuration. The time tool, on the other hand, exposes the current system clock to the assistant, enabling real‑time date and time queries without needing external APIs or network calls. Though minimal, these features illustrate how an MCP server can expose arbitrary Python logic in a declarative, reproducible manner.

Key features of this implementation include:

• Nix‑based isolation: The entire runtime, including the Python interpreter and dependencies, is encapsulated in a Nix derivation. This guarantees that anyone running the server will have an identical environment.
• Zero‑config startup: Once the Nix flake is fetched, starting the server requires a single command. No environment variables or manual path adjustments are necessary.
• Extensible tool set: The architecture is intentionally simple, yet it can be expanded by adding new Python modules or scripts. Each new tool follows the same pattern—expose a function, register it in the MCP schema, and add an entry to the configuration file.
• Plug‑and‑play with Claude: The README provides a ready‑to‑copy configuration snippet for adding the server to a Claude setup. After registration, the assistant can call just like any built‑in tool.

Real‑world use cases arise whenever developers need a quick, reliable way to expose internal tooling or data sources to an AI assistant. For instance:

• Internal dashboards: A team can expose a tool that fetches the latest build status from CI pipelines, allowing Claude to report on pipeline health during stand‑ups.
• Time‑sensitive workflows: The time tool can be used in scheduling or deadline calculations, ensuring the assistant always works with the host’s clock.
• Proof‑of‑concepts: The minimal setup is ideal for experimenting with MCP integration in a sandbox before scaling to more complex services.

By leveraging Nix’s declarative package management, this MCP server offers a robust yet lightweight foundation for developers to connect AI assistants to their own tools and data sources. Its simplicity makes it an excellent starting point for building more sophisticated MCP services while maintaining reproducibility and ease of deployment.