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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.

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Example

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Extends

  • SpanBase

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Properties

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args

readonly args: string

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name

readonly name: string

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result

Deprecated. Pass result to end() instead.
optional result: string
Tool output as a string. Prefer passing result to end().

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toolCallId

readonly toolCallId: string

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Methods

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addEvent()

Deprecated. Record this data via 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/
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.

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Parameters

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string
required
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Attributes
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TimeInput

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Returns

this

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Example

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Inherited from

SpanBase.addEvent

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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.

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Parameters

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ToolEndOptions
See ToolEndOptions.

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Returns

void

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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).

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Parameters

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Attributes
required

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Returns

this

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Example

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Inherited from

SpanBase.setAttributes