FunctionTool

Defined in: src/tools/function-tool.ts:91

A Tool implementation that wraps a callback function and handles all ToolResultBlock conversion.

FunctionTool allows creating tools from existing functions without needing to manually handle ToolResultBlock formatting or error handling. It supports multiple callback patterns:

Async generators for streaming responses
Promises for async operations
Synchronous functions for immediate results

All return values are automatically wrapped in ToolResultBlock, and errors are caught and returned as error ToolResultBlocks.

Example

// Create a tool with streaming
const streamingTool = new FunctionTool({
  name: 'processor',
  description: 'Processes data with progress updates',
  inputSchema: { type: 'object', properties: { data: { type: 'string' } } },
  callback: async function* (input: any) {
    yield 'Starting processing...'
    // Do some work
    yield 'Halfway done...'
    // More work
    return 'Processing complete!'
  }
})

Extends

Tool

Constructors

Constructor

new FunctionTool(config): FunctionTool;

Defined in: src/tools/function-tool.ts:139

Creates a new FunctionTool instance.

Parameters

Parameter	Type	Description
`config`	`FunctionToolConfig`	Configuration object for the tool

Returns

FunctionTool

Example

// Tool with input schema
const greetTool = new FunctionTool({
  name: 'greeter',
  description: 'Greets a person by name',
  inputSchema: {
    type: 'object',
    properties: { name: { type: 'string' } },
    required: ['name']
  },
  callback: (input: any) => `Hello, ${input.name}!`
})

// Tool without input (no parameters)
const statusTool = new FunctionTool({
  name: 'getStatus',
  description: 'Gets system status',
  callback: () => ({ status: 'operational' })
})

Overrides

Tool.constructor

Properties

name

readonly name: string;

Defined in: src/tools/function-tool.ts:95

The unique name of the tool.

Overrides

Tool.name

description

readonly description: string;

Defined in: src/tools/function-tool.ts:100

Human-readable description of what the tool does.

Overrides

Tool.description

toolSpec

readonly toolSpec: ToolSpec;

Defined in: src/tools/function-tool.ts:105

OpenAPI JSON specification for the tool.

Overrides

Tool.toolSpec

Methods

stream()

stream(toolContext): AsyncGenerator<ToolStreamEvent, ToolResultBlock, unknown>;

Defined in: src/tools/function-tool.ts:166

Executes the tool with streaming support. Handles all callback patterns (async generator, promise, sync) and converts results to ToolResultBlock.

Parameters

Parameter	Type	Description
`toolContext`	`ToolContext`	Context information including the tool use request and invocation state

Returns

AsyncGenerator<ToolStreamEvent, ToolResultBlock, unknown>

Async generator that yields ToolStreamEvents and returns a ToolResultBlock

Overrides

Tool.stream