Tool

Defined in: src/tools/tool.ts:92

Interface for tool implementations. Tools are used by agents to interact with their environment and perform specific actions.

The Tool interface provides a streaming execution model where tools can yield progress events during execution before returning a final result.

Most implementations should use FunctionTool rather than implementing this interface directly.

Extended by

• InvokableTool
• FunctionTool

Constructors

Constructor

new Tool(): Tool;

Returns

Tool

Properties

name

abstract name: string;

Defined in: src/tools/tool.ts:97

The unique name of the tool. This MUST match the name in the toolSpec.

---

description

abstract description: string;

Defined in: src/tools/tool.ts:104

Human-readable description of what the tool does. This helps the model understand when to use the tool.

This MUST match the description in the toolSpec.description.

---

toolSpec

abstract toolSpec: ToolSpec;

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

OpenAPI JSON specification for the tool. Defines the tool’s name, description, and input schema.

Methods

stream()

abstract stream(toolContext): ToolStreamGenerator;

Defined in: src/tools/tool.ts:144

Executes the tool with streaming support. Yields zero or more ToolStreamEvents during execution, then returns exactly one ToolResultBlock as the final value.

Parameters

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

Returns

ToolStreamGenerator

Async generator that yields ToolStreamEvents and returns a ToolResultBlock

Example

const context = {
  toolUse: {
    name: 'calculator',
    toolUseId: 'calc-123',
    input: { operation: 'add', a: 5, b: 3 }
  },
}

// The return value is only accessible via explicit .next() calls
const generator = tool.stream(context)
for await (const event of generator) {
  // Only yields are captured here
  console.log('Progress:', event.data)
}
// Or manually handle the return value:
let result = await generator.next()
while (!result.done) {
  console.log('Progress:', result.value.data)
  result = await generator.next()
}
console.log('Final result:', result.value.status)