How to get environment variables on the server?

[ilvalerione]

Question

I haven't been able to figure out how to get environment variables in tool functions on an MCP server, or if they're actually supported.

This should be a valid client configuration:

{
    "mcpServers": {
        "php-calculator": {
            "command": "python",
            "args": ["/absolute/path/to/your/mcp-server.py"], 
            "env": {"API_KEY": "xxxx"}
        }
    }
}

How can I get the API_KEY environment variable on the server?

Additional Context

No response

[felixweinberger]

This depends on the environment you're running your MCP server in - there's an example for desktop in the README here: https://github.com/modelcontextprotocol/python-sdk?tab=readme-ov-file#claude-desktop-integration

But probably worth adding something to docs on patterns for how to deal with this common use case.

[ameenalkhaldi]

I've opened a PR addressing this: #2296

Added a dedicated documentation page covering environment variable patterns — accessing them in tool functions, passing them via Claude Desktop config / mcp install CLI / programmatic clients, and the built-in MCP_-prefixed settings.