> ## Documentation Index
> Fetch the complete documentation index at: https://docs.wandb.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Class: Turn

> TypeScript SDK reference

[weave](../) / Turn

An agent invocation. Typically wraps the work to respond to a single
user message. Emits an `invoke_agent` span and acts as the root of the
trace for that turn: it is always started under `ROOT_CONTEXT` so it
never accidentally inherits a parent from another OTel-instrumented
library.

Created by `weave.startTurn()` (or `session.startTurn()`) and
terminated with `end()`. Only one Turn may be active in an async chain.
Children (LLM, Tool, SubAgent) attach via the `startLLM`, `startTool`,
`startSubagent` methods.

`Example`

```ts theme={null}
const turn = weave.startTurn({agentName: 'research-bot', model: MODEL});
try {
  const llm = turn.startLLM({model: MODEL, providerName: 'openai'});
  // ...
  llm.end();
} finally {
  turn.end();
}
```

## Table of contents

### Properties

* [agentName](./turn#agentname)
* [model](./turn#model)

### Methods

* [addEvent](./turn#addevent)
* [end](./turn#end)
* [setAttribute](./turn#setattribute)
* [startLLM](./turn#startllm)
* [startSubagent](./turn#startsubagent)
* [startTool](./turn#starttool)
* [create](./turn#create)

## Properties

### agentName

• `Readonly` **agentName**: `string`

#### Defined in

[genai/turn.ts:60](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L60)

***

### model

• `Readonly` **model**: `string`

#### Defined in

[genai/turn.ts:61](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L61)

## Methods

### addEvent

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

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

#### Parameters

| Name          | Type         |
| :------------ | :----------- |
| `name`        | `string`     |
| `attributes?` | `Attributes` |
| `startTime?`  | `TimeInput`  |

#### Returns

`this`

`Example`

```ts theme={null}
turn.addEvent('context_compacted', {removedMessages: 12});
```

#### Defined in

[genai/turn.ts:152](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L152)

***

### end

▸ **end**(`opts?`): `void`

Close the Turn span. Idempotent. Pass `error` to mark it as failed.

#### Parameters

| Name          | Type     |
| :------------ | :------- |
| `opts?`       | `Object` |
| `opts.error?` | `Error`  |

#### Returns

`void`

#### Defined in

[genai/turn.ts:159](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L159)

***

### setAttribute

▸ **setAttribute**(`key`, `value`): `this`

Set a single attribute on the Turn span. Useful for stamping running
totals (e.g. cumulative cost, token usage) or other metadata that becomes
known mid-turn. No-op after `end()`. Mirrors OTel `Span.setAttribute`.

#### Parameters

| Name    | Type             |
| :------ | :--------------- |
| `key`   | `string`         |
| `value` | `AttributeValue` |

#### Returns

`this`

`Example`

```ts theme={null}
turn.setAttribute('gen_ai.usage.input_tokens', totalInputTokens);
```

#### Defined in

[genai/turn.ts:138](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L138)

***

### startLLM

▸ **startLLM**(`opts`): [`LLM`](./llm)

Start a child LLM span under this Turn.

#### Parameters

| Name   | Type                               |
| :----- | :--------------------------------- |
| `opts` | [`LLMInit`](../interfaces/llminit) |

#### Returns

[`LLM`](./llm)

#### Defined in

[genai/turn.ts:104](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L104)

***

### startSubagent

▸ **startSubagent**(`opts`): [`SubAgent`](./subagent)

Start a child SubAgent span under this Turn.

#### Parameters

| Name   | Type                                         |
| :----- | :------------------------------------------- |
| `opts` | [`SubAgentInit`](../interfaces/subagentinit) |

#### Returns

[`SubAgent`](./subagent)

#### Defined in

[genai/turn.ts:122](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L122)

***

### startTool

▸ **startTool**(`opts`): [`Tool`](./tool)

Start a child Tool span under this Turn.

#### Parameters

| Name   | Type                                 |
| :----- | :----------------------------------- |
| `opts` | [`ToolInit`](../interfaces/toolinit) |

#### Returns

[`Tool`](./tool)

#### Defined in

[genai/turn.ts:113](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L113)

***

### create

▸ **create**(`opts?`): [`Turn`](./turn)

#### Parameters

| Name   | Type                                                                     |
| :----- | :----------------------------------------------------------------------- |
| `opts` | [`TurnInit`](../interfaces/turninit) & \{ `conversationId?`: `string`  } |

#### Returns

[`Turn`](./turn)

#### Defined in

[genai/turn.ts:64](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/turn.ts#L64)