While large language models (LLMs) have incredible generation capabilities, they struggle with discrete tasks (e.g. mathematics) and interacting with the outside world (e.g. getting the weather).

Tools can be thought of as programs you give to a model which can be run as and when the model deems applicable.

What is a tool?

A tool is an object that can be called by the model to perform a specific task. You can use tools with functions across the AI SDK (like generateText or streamUI) by passing a tool(s) to the tools parameter.

There are three elements of a tool, a description, parameters, and an optional execute or generate function (dependent on the SDK function).

  • description: An optional description of the tool that can influence when the tool is picked.
  • parameters: A Zod schema that defines the parameters. It is converted to a JSON schema that is consumed by the LLM, and also used to validate the LLM tool calls.
  • execute or generate: An optional async or generator function that is called with the arguments from the tool call.

Tool Calls

If the LLM decides to use a tool, it will generate a tool call. Tools with an execute or generate function are run automatically when these calls are generated. The results of the tool calls are returned using tool result objects. Each tool result object has a toolCallId, a toolName, a typed args object, and a typed result.

Tool Choice

You can use the toolChoice setting to influence when a tool is selected. It supports the following settings:

  • auto (default): the model can choose whether and which tools to call.
  • required: the model must call a tool. It can choose which tool to call.
  • none: the model must not call tools
  • { type: 'tool', toolName: string (typed) }: the model must call the specified tool
import { z } from 'zod';
import { generateText, tool } from 'ai';
const result = await generateText({
model: yourModel,
tools: {
weather: tool({
description: 'Get the weather in a location',
parameters: z.object({
location: z.string().describe('The location to get the weather for'),
execute: async ({ location }) => ({
temperature: 72 + Math.floor(Math.random() * 21) - 10,
toolChoice: 'required', // force the model to call a tool
'What is the weather in San Francisco and what attractions should I visit?',

Schema Specification and Validation with Zod

Tool usage and structured object generation require the specification of schemas. The AI SDK uses Zod, the most popular JavaScript schema validation library, for schema specification and validation.

You can install Zod with:

pnpm install zod

You can then specify schemas, for example:

import z from 'zod';
const recipeSchema = z.object({
recipe: z.object({
name: z.string(),
ingredients: z.array(
name: z.string(),
amount: z.string(),
steps: z.array(z.string()),

These schemas can be used to define parameters for tool calls and generated structured objects with generateObject and streamObject.