createTool()

The createTool() function is used to define custom tools that your Mastra agents can execute. Tools extend an agent’s capabilities by allowing it to interact with external systems, perform calculations, or access specific data.

Usage example

src/mastra/tools/reverse-tool.ts


import { createTool } from "@mastra/core/tools";
import { z } from "zod";
 
export const tool = createTool({
  id: "test-tool",
  description: "Reverse the input string",
  inputSchema: z.object({
    input: z.string()
  }),
  outputSchema: z.object({
    output: z.string()
  }),
  execute: async ({ context }) => {
    const { input } = context;
    const reversed = input.split("").reverse().join("");
 
    return {
      output: reversed
    };
  }
});

Parameters

id:

string

A unique identifier for the tool.

description:

string

A description of what the tool does. This is used by the agent to decide when to use the tool.

inputSchema?:

Zod schema

A Zod schema defining the expected input parameters for the tool's `execute` function.

outputSchema?:

Zod schema

A Zod schema defining the expected output structure of the tool's `execute` function.

execute:

function

The function that contains the tool's logic. It receives an object with `context` (the parsed input based on `inputSchema`), `runtimeContext`, and an object containing `abortSignal`.

Returns

The createTool() function returns a Tool object.

Tool:

object

An object representing the defined tool, ready to be added to an agent.