Tools Give AI Hands

Tools are functions the AI can call to fetch data or mutate state. They are the most powerful part of MCP.

Registering a Tool with Zod

The TypeScript SDK highly recommends using the zod library for argument validation.

import { z } from "zod";

server.tool(
  "calculate_tax",
  "Calculate sales tax for a given purchase amount",
  {
    amount: z.number().describe("The total purchase amount"),
    param_state: z.string().describe("Two-letter state code")
  },
  async ({ amount, param_state }) => {
    return { content: [{ type: "text", text: `Tax is high in ${param_state}` }] };
  }
);