Build a Local TypeScript MCP Server

mkdir order-mcp && cd order-mcp
npm init -y
npm install @modelcontextprotocol/server zod
npm install -D typescript tsx @types/node

{
  "scripts": {
    "dev": "tsx src/index.ts",
    "build": "tsc",
    "start": "node dist/index.js"
  },
  "type": "module"
}

src/
  domain/order.ts
  services/order-service.ts
  tools/register-order-tools.ts
  index.ts
tests/
  order-tool.test.ts

import { McpServer } from "@modelcontextprotocol/server";
import { StdioServerTransport } from "@modelcontextprotocol/server/stdio";
import * as z from "zod/v4";

const orders = new Map([
  ["ORD-101", { id: "ORD-101", status: "shipped" }],
]);

const server = new McpServer({ name: "order-learning-server", version: "1.0.0" });

server.registerTool(
  "orders.lookup",
  {
    description: "Look up one mock order by ID",
    inputSchema: z.object({ orderId: z.string().regex(/^ORD-\d+$/) }),
    outputSchema: z.object({ id: z.string(), status: z.string() }),
  },
  async ({ orderId }) => {
    const order = orders.get(orderId);
    if (!order) {
      return { content: [{ type: "text", text: "Order not found" }], isError: true };
    }
    return {
      content: [{ type: "text", text: JSON.stringify(order) }],
      structuredContent: order,
    };
  },
);

const transport = new StdioServerTransport();
await server.connect(transport);