Tools are defined using the createTool function. 
import { createTool } from '@inngest/agent-kit';

const tool = createTool({
  name: 'write-file',
  description: 'Write a file to disk with the given contents',
  parameters: {
    type: 'object',
    properties: {
      path: {
        type: 'string',
        description: 'The path to write the file to',
      },
      contents: {
        type: 'string',
        description: 'The contents to write to the file',
      },
    },
    required: ['path', 'contents'],
  },
  handler: async ({ path, contents }, { agent, network }) => {
    await fs.writeFile(path, contents);
    return { success: true };
  },
});

​
Options

​
name
string
required
The name of the tool. Used by the model to identify which tool to call.
​
description
string
required
A clear description of what the tool does. This helps the model understand when and how to use the tool.
​
parameters
JSONSchema | ZodType
required
A JSON Schema object or Zod type that defines the parameters the tool accepts. This is used to validate the model’s inputs and provide type safety.
​
handler
function
required
The function that executes when the tool is called. It receives the validated parameters as its first argument and a context object as its second argument.
​
strict
boolean
default:true
Option to disable strict validation of the tool parameters.
​
lifecycle
Lifecycle
Lifecycle hooks that can intercept and modify inputs and outputs throughout the stages of tool execution.

​
Handler Function

The handler function receives two arguments:
  1. input: The validated parameters matching your schema definition
  2. context: An object containing:
    • agent: The Agent instance that called the tool
    • network: The network instance, providing access to the network.state.
Example handler with full type annotations: 
import { createTool } from '@inngest/agent-kit';

const tool = createTool({
  name: 'write-file',
  description: 'Write a file to disk with the given contents',
  parameters: {
    type: 'object',
    properties: {
      path: { type: 'string' },
      contents: { type: 'string' },
    },
  },
  handler: async ({ path, contents }, { agent, network }) => {
    await fs.writeFile(path, contents);
    network.state.fileWritten = true;
    return { success: true };
  },
});

​
lifecycle

​
onStart
function
Called before the tool handler is executed. The onStart hook can be used to:
  • Modify input parameters before they are passed to the handler
  • Prevent the tool from being called by throwing an error
​
onFinish
function
Called after the tool handler has completed. The onFinish hook can be used to:
  • Modify the result before it is returned to the agent
  • Perform cleanup operations
const tool = createTool({
  name: 'write-file',
  lifecycle: {
    onStart: ({ parameters }) => {
      // Validate or modify parameters before execution
      return parameters;
    },
  },
});