Model Context Protocol Server Guide

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import {
  CallToolRequestSchema,
  ListToolsRequestSchema,
} from "@modelcontextprotocol/sdk/types.js";

// 1. Initialize MCP Server
const server = new Server(
  { name: "my-custom-server", version: "1.0.0" },
  { capabilities: { tools: {} } }
);

// 2. Define exposed tools
server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [
      {
        name: "calculate_tax",
        description: "Calculate sales tax for a transaction",
        inputSchema: {
          type: "object",
          properties: {
            amount: { type: "number", description: "Transaction amount in USD" },
            state: { type: "string", description: "Two-letter US state code" },
          },
          required: ["amount", "state"],
        },
      },
    ],
  };
});

// 3. Handle tool invocation
server.setRequestHandler(CallToolRequestSchema, async (request) => {
  if (request.params.name === "calculate_tax") {
    const { amount, state } = request.params.arguments as { amount: number; state: string };
    const rate = state === "CA" ? 0.0725 : 0.05;
    const tax = amount * rate;
    return {
      content: [{ type: "text", text: `Tax for ${state} on $${amount} is $${tax.toFixed(2)}` }],
    };
  }
  throw new Error("Tool not found");
});

// 4. Connect via stdio
const transport = new StdioServerTransport();
await server.connect(transport);
console.error("MCP Server running on stdio");