ERP MCP Server Python Skeleton (FastMCP Generator)

import os
import re

import requests
from mcp.server.fastmcp import FastMCP

mcp = FastMCP("erp-readonly")

BASE_URL = "https://erp.example.com/api/v1"
ID_PATTERN = re.compile(r"^[A-Z0-9-]{4,20}$")


@mcp.tool()
def get_sales_order(order_number: str) -> str:
    """Look up one record by its identifier. Read only, never changes ERP data."""
    if not ID_PATTERN.match(order_number):
        return "Rejected: order_number must match the pattern [A-Z0-9-]{4,20}."

    token = os.environ.get("ERP_API_TOKEN")
    if not token:
        return "Server is not configured: credentials are missing."

    try:
        response = requests.get(
            BASE_URL + "/salesorders/" + order_number,
            headers={"Authorization": "Bearer " + token, "Accept": "application/json"},
            timeout=15,
        )
    except requests.RequestException:
        return "The ERP could not be reached. Try again later."

    if response.status_code == 404:
        return "No record found for that identifier."
    if response.status_code in (401, 403):
        return "The service account is not permitted to read this record."
    if response.status_code != 200:
        return "The ERP returned an error (HTTP " + str(response.status_code) + ")."

    data = response.json()
    # Return only the fields the model needs, never the whole record
    keep = ["id", "customer", "status", "total", "currency"]
    slim = {key: data.get(key) for key in keep}
    return str(slim)


if __name__ == "__main__":
    mcp.run(transport="stdio")

pip install "mcp[cli]" requests
export ERP_API_TOKEN=your-token
python server.py