Practical MCP with FastMCP & LangChain

Step 1 - Startup, Configuration and Preparation

When the host starts, it loads MCP connection settings. This usually includes:

• Which servers are enabled
• Which transport each server uses (STDIO or HTTP)
• Endpoint URLs or local launch commands
• Auth settings (tokens, API keys, headers)
• Optional timeouts, retry rules, and rate limits

For this example, the host learns that the air-quality server is remote: http://mcp.airquality.com. It also learns the auth token it needs to connect. This can be done using a configuration file on the host side. For example, the host might load a JSON config file like this:

{
  "mcpServers": {
    "airQuality": {
      "transport": "streamable-http",
      "endpoint": "http://mcp.airquality.com/connect",
      "headers": {
        "x-api-key": "xxx-abc-123"
      },
      "timeout": 5000
    }
  }
}