Class: Tool

TypeScript SDK reference

weave / Tool

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

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();
}

Hierarchy

• SpanBase

  ↳ Tool

Table of contents

Properties

• args
• name
• result
• toolCallId

Methods

• addEvent
• end
• setAttributes
• create

Properties

args

• Readonly args: string

Defined in

src/genai/tool.ts:52

---

name

• Readonly name: string

Defined in

src/genai/tool.ts:51

---

result

• Optional result: string

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

Defined in

src/genai/tool.ts:47

---

toolCallId

• Readonly toolCallId: string

Defined in

src/genai/tool.ts:53

Methods

addEvent

▸ 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

Name	Type
name	string
attributes?	Attributes
startTime?	TimeInput

Returns

this

Example

span.addEvent('context_compacted', {removedMessages: 12});

Inherited from

SpanBase.addEvent

Defined in

src/genai/spanBase.ts:77

---

end

▸ end(opts?): void

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

Parameters

Name	Type
opts?	SpanEndOptions

Returns

void

Defined in

src/genai/tool.ts:87

---

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

Name	Type
attributes	Attributes

Returns

this

Example

span.setAttributes({'weave.tag': 'prod', 'gen_ai.response.id': id});

Inherited from

SpanBase.setAttributes

Defined in

src/genai/spanBase.ts:63

---

create

▸ create(opts): Tool

Parameters

Name	Type
opts	ToolInit & ChildSpanContext

Returns

Tool

Defined in

src/genai/tool.ts:58