> ## Documentation Index
> Fetch the complete documentation index at: https://wb-21fd5541-typedoc-upgrade.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Tool

> TypeScript SDK reference

Defined in: [src/genai/tool.ts:43](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L43)

A tool invocation. Emits an `execute_tool` span carrying the tool name,
the JSON-encoded arguments, the tool-call id, and the result.

Created by `weave.startTool()` (or `turn.startTool()`, or
`llm.startTool()`) and terminated with `end()`. Assign `result` before
calling `end()` to record the tool's output on the span.

## Example

```ts twoslash theme={null}
// @noErrors
const tool = weave.startTool({
  name: tc.function.name,
  args: tc.function.arguments,
  toolCallId: tc.id,
});
try {
  tool.result = await wikipediaSearch(JSON.parse(tc.function.arguments));
} finally {
  tool.end();
}
```

## Extends

* `SpanBase`

## Properties

### args

> `readonly` **args**: `string`

Defined in: [src/genai/tool.ts:52](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L52)

***

### name

> `readonly` **name**: `string`

Defined in: [src/genai/tool.ts:51](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L51)

***

### result?

> `optional` **result?**: `string`

Defined in: [src/genai/tool.ts:47](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L47)

Tool output as a string. Recorded on `gen_ai.tool.call.result` at `end()`.

***

### toolCallId

> `readonly` **toolCallId**: `string`

Defined in: [src/genai/tool.ts:53](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L53)

## Methods

### ~~addEvent()~~

<Warning>
  **Deprecated.** Record this data via [setAttributes](#setattributes) instead.
  OpenTelemetry is phasing out the Span Event API (`Span.addEvent`). This
  method still works and existing span-event data stays valid.
  See [https://opentelemetry.io/blog/2026/deprecating-span-events/](https://opentelemetry.io/blog/2026/deprecating-span-events/)
</Warning>

> **addEvent**(`name`, `attributes?`, `startTime?`): `this`

Defined in: [src/genai/spanBase.ts:82](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/spanBase.ts#L82)

Add a named event to the span. Useful for marking non-span moments such as
context compaction, tool-loop detection, or guardrail trips. Warns and
no-ops after `end()`. Mirrors OTel `Span.addEvent`.

#### Parameters

##### name

`string`

##### attributes?

`Attributes`

##### startTime?

`TimeInput`

#### Returns

`this`

#### Example

```ts twoslash theme={null}
// @noErrors
span.addEvent('context_compacted', {removedMessages: 12});
```

#### Inherited from

`SpanBase.addEvent`

***

### end()

> **end**(`opts?`): `void`

Defined in: [src/genai/tool.ts:87](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/tool.ts#L87)

Flush `result` to the span and close it. Idempotent. Pass `error` to mark
the span as failed; pass `endTime` to backdate the close.

#### Parameters

##### opts?

`SpanEndOptions`

#### Returns

`void`

***

### setAttributes()

> **setAttributes**(`attributes`): `this`

Defined in: [src/genai/spanBase.ts:63](https://github.com/wandb/weave/blob/8c5f077eb11c42b84000726ff20504abc728d3fb/sdks/node/src/genai/spanBase.ts#L63)

Set multiple attributes on the span at once. Warns and no-ops after
`end()`. Mirrors OTel `Span.setAttributes` (and the Python SDK's
`set_attributes`).

#### Parameters

##### attributes

`Attributes`

#### Returns

`this`

#### Example

```ts twoslash theme={null}
// @noErrors
span.setAttributes({'weave.tag': 'prod', 'gen_ai.response.id': id});
```

#### Inherited from

`SpanBase.setAttributes`