Let Claude call your own TypeScript functions with tool use

Let Claude call your own TypeScript functions with tool use | Wirestack

What you get

Claude decides when to call your own TypeScript function, runs it through the SDK's tool runner, and answers using the result.

Prerequisites

An Anthropic API key from the Claude Console
Node.js 20 LTS or later
Zod 3.25.0 or higher (required by betaZodTool)

Steps

Install the SDK, Zod, and tsx to run TypeScript directly.

Shell


npm install @anthropic-ai/sdk zod

npm install --save-dev tsx

Set your API key.

Shell


export ANTHROPIC_API_KEY="your-anthropic-api-key"

Create index.ts. betaZodTool turns your function into a tool with a validated input schema, and runs the loop: Claude asks for the tool, the SDK calls , sends the result back, and repeats until Claude has a final answer.

client.beta.messages.toolRunner

run

typescript


import Anthropic from "@anthropic-ai/sdk";

import { betaZodTool } from "@anthropic-ai/sdk/helpers/beta/zod";

import { z } from "zod";



const client = new Anthropic();



// Your own function. Swap the body for a database query or an internal API call.

async function getWeather(location: string, unit: "celsius" | "fahrenheit") {

  return { location, temperature: unit === "celsius" ? "20°C" : "68°F", condition: "Sunny" };

}



const getWeatherTool = betaZodTool({

  name: "get_weather",

  description: "Get the current weather in a given location",

  inputSchema: z.object({

    location: z.string().describe("The city and state, e.g. San Francisco, CA"),

    unit: z.enum(["celsius", "fahrenheit"]).default("fahrenheit").describe("Temperature unit")

  }),

  run: async (input) => {

    return JSON.stringify(await getWeather(input.location, input.unit));

  }

});



async function main() {

  const finalMessage = await client.beta.messages.toolRunner({

    model: "claude-opus-5-5",

    max_tokens: 1024,

    tools: [getWeatherTool],

    messages: [{ role: "user", content: "What's the weather like in Paris?" }]

  });



  for (const block of finalMessage.content) {

    if (block.type === "text") {

      console.log(block.text);

    }

  }

}



main();

Let Claude call your own TypeScript functions with tool use

What you'll need

What you get

Prerequisites

Steps

Test it