> ## 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.

# startTool

> TypeScript SDK reference

# startTool

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

Start a Tool span. Parent resolution (matches the design's "flat by
default, hierarchical if you nest"):

* If an LLM is active, the Tool nests under it.
* Otherwise, the Tool is a sibling under the current Turn.

Throws if neither a Turn nor an LLM is active.

#### Parameters

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

#### Returns

[`Tool`](../classes/tool)

#### Defined in

[genai/api.ts:50](https://github.com/wandb/weave/blob/6538626556c93d6f31ae725fdefe4e6b8b71bc2c/sdks/node/src/genai/api.ts#L50)

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