child_runs=[],
            run_type="tool",
            tags=tags or [],
            name=name,
        )
        self._start_trace(tool_run)
        self._on_tool_start(tool_run)
        return tool_run
[docs]    def on_tool_end(self, output: str, *, run_id: UUID, **kwargs: Any) -> Run:
        """End a trace for a tool run."""
        tool_run = self._get_run(run_id, run_type="tool")
        tool_run.outputs = {"output": output}
        tool_run.end_time = datetime.utcnow()
        tool_run.events.append({"name": "end", "time": tool_run.end_time})
        self._end_trace(tool_run)
        self._on_tool_end(tool_run)
        return tool_run
[docs]    def on_tool_error(
        self,
        error: BaseException,
        *,
        run_id: UUID,
        **kwargs: Any,
    ) -> Run:
        """Handle an error for a tool run."""
        tool_run = self._get_run(run_id, run_type="tool")
        tool_run.error = self._get_stacktrace(error)
        tool_run.end_time = datetime.utcnow()
        tool_run.events.append({"name": "error", "time": tool_run.end_time})
        self._end_trace(tool_run)
        self._on_tool_error(tool_run)
        return tool_run
[docs]    def on_retriever_start(
        self,
        serialized: Dict[str, Any],
        query: str,
        *,
        run_id: UUID,
        parent_run_id: Optional[UUID] = None,
        tags: Optional[List[str]] = None,
        metadata: Optional[Dict[str, Any]] = None,