> ## Documentation Index
> Fetch the complete documentation index at: https://wb-21fd5541-docs-2516.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# Tool
> TypeScript SDK reference
export const GitHubLink = ({url, compact = false}) =>
{compact ? "View source" : <>
GitHub source
}
;
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.
## 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`
***
### name
> `readonly` **name**: `string`
***
### ~~result~~
**Deprecated.** Pass `result` to `end()` instead.
> `optional` **result**: `string`
Tool output as a string. Prefer passing `result` to `end()`.
***
### toolCallId
> `readonly` **toolCallId**: `string`
## Methods
### ~~addEvent()~~
**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/)
> **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`.
#### Parameters
#### 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.
#### Parameters
See [`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`).
#### Parameters
#### Returns
`this`
#### Example
```ts twoslash theme={null}
// @noErrors
span.setAttributes({'weave.tag': 'prod', 'gen_ai.response.id': id});
```
#### Inherited from
`SpanBase.setAttributes`