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

# Tool

> TypeScript SDK reference

A tool invocation. Emits an `execute_tool` span carrying the tool name,
the arguments, the tool-call id, and the result. String arguments and
results are recorded as-is; other JSON values are serialized.

Created by `weave.startTool()` (or `turn.startTool()`, or
`llm.startTool()`) and terminated with `end()`, which accepts the result and
optional error metadata.

Defined in: [src/genai/tool.ts:65](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L65)

## Example

```ts twoslash theme={null}
// @noErrors
const tool = weave.startTool({name: 'get_weather', args: {city: 'Tokyo'}});
try {
  const result = await getWeather('Tokyo');
  tool.end({result});
} catch (error) {
  tool.end({error: error as Error, errorType: 'weather_error'});
  throw error;
}
```

## Extends

* `SpanBase`

## Properties

### args

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

Defined in: [src/genai/tool.ts:76](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L76)

***

### name

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

Defined in: [src/genai/tool.ts:75](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L75)

***

### ~~result~~

<Warning>
  **Deprecated.** Pass `result` to `end()` instead.
</Warning>

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

Tool output as a string. Prefer passing `result` to `end()`.

Defined in: [src/genai/tool.ts:71](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L71)

***

### toolCallId

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

Defined in: [src/genai/tool.ts:77](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L77)

## 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`

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`.

Defined in: [src/genai/spanBase.ts:84](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/spanBase.ts#L84)

#### 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`

Record an optional result and error type, then close the span. Idempotent.
Pass `error` to mark the span as failed and `endTime` to backdate the close.

Defined in: [src/genai/tool.ts:111](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/tool.ts#L111)

#### Parameters

##### opts?

[`ToolEndOptions`](./toolendoptions)

#### Returns

`void`

***

### setAttributes()

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

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`).

Defined in: [src/genai/spanBase.ts:65](https://github.com/wandb/weave/blob/7c9efdc9fe05ffcaf2430dd652ef9bc5b3ffdfaa/sdks/node/src/genai/spanBase.ts#L65)

#### 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`