Practical MCP with FastMCP & LangChain

cat > main.py << EOF
import os
from typing import Annotated
from dotenv import load_dotenv
from pydantic import Field
from fastmcp import FastMCP
from fastmcp.dependencies import Depends

load_dotenv()

def get_age_multiplier() -> int:
    """Load the age multiplier from environment variables."""
    return int(os.getenv("DOG_AGE_MULTIPLIER", "7"))

mcp = FastMCP(
    name=os.getenv("MCP_NAME"),
    list_page_size=int(os.getenv("MCP_LIST_PAGE_SIZE", "10")),
    instructions=os.getenv("MCP_INSTRUCTIONS"),
)

@mcp.tool
def dog_to_human_age(
    age: Annotated[int, Field(ge=0, le=30, description="The dog's age in years")],
    multiplier: int = Depends(get_age_multiplier),
) -> int:
    """Calculate the real age of a dog in human years."""
    return age * multiplier
EOF

cat > .env << EOF
MCP_NAME="Puppy Guide"
MCP_LIST_PAGE_SIZE=10