Hello World UV Runtime Example

This example demonstrates a minimal MCP server using UV runtime.

What is UV Runtime?

UV runtime lets Claude Desktop automatically manage Python and dependencies for your extension:

• Downloads the correct Python version for the user's platform
• Creates an isolated virtual environment
• Installs dependencies from pyproject.toml
• Works cross-platform (Windows, macOS, Linux) without user setup

Structure

hello-world-uv/
├── manifest.json       # server.type = "uv"
├── pyproject.toml      # Dependencies listed here
├── .mcpbignore        # Exclude build artifacts
└── src/
    └── server.py       # MCP server implementation

Key Differences from Python Runtime

UV Runtime (this example):

• server.type = "uv"
• No bundled dependencies
• mcp_config uses uv run to auto-resolve deps from pyproject.toml
• Small bundle size (~2 KB)
• Works on any platform

Python Runtime (traditional):

• server.type = "python"
• Must bundle dependencies in server/lib/
• Requires mcp_config with PYTHONPATH
• Larger bundle size
• Only works with pure Python (no compiled deps)

Installing

mcpb pack

Install the generated .mcpb file in Claude Desktop.

Testing Locally

# Install dependencies
uv sync

# Run server
uv run src/server.py

Tools

• say_hello - Greets a person by name