FunctionTool

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

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

Implements

• InvokableTool<unknown, JSONValue>

Constructors

Constructor

new FunctionTool(config): FunctionTool;

Defined in: src/tools/function-tool.ts:148

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:104

The unique name of the tool.

Implementation of

InvokableTool.name

Overrides

Tool.name

---

description

readonly description: string;

Defined in: src/tools/function-tool.ts:109

Human-readable description of what the tool does.

Implementation of

InvokableTool.description

Overrides

Tool.description

---

toolSpec

readonly toolSpec: ToolSpec;

Defined in: src/tools/function-tool.ts:114

OpenAPI JSON specification for the tool.

Implementation of

InvokableTool.toolSpec

Overrides

Tool.toolSpec

Methods

stream()

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

Defined in: src/tools/function-tool.ts:175

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

Implementation of

InvokableTool.stream

Overrides

Tool.stream

---

invoke()

invoke(input, context?): Promise<JSONValue>;

Defined in: src/tools/function-tool.ts:229

Invokes the tool directly with raw input and returns the unwrapped result.

Unlike stream(), this method:

• Returns the raw result (not wrapped in ToolResult)
• Consumes async generators and returns the generator’s return value
• Lets errors throw naturally (not wrapped in error ToolResult)

Parameters

| Parameter | Type | Description | | ---------- | -------------------------------- | --------------------------------- | | input | unknown | The input parameters for the tool | | context? | ToolContext | Optional tool execution context |

Returns

Promise<JSONValue>

The unwrapped result

Implementation of

InvokableTool.invoke