on_tool_start() — langchain Function Reference

Architecture documentation for the on_tool_start() function in manager.py from the langchain codebase.

Function python Observability CallbackManager calls 2 called by 1

Entity Profile

Observability→ CallbackManager→ on_tool_start() — langchain Function Reference

Dependency Diagram

graph TD
  99e09f49_82fe_9b97_1a99_8b1db9974286["on_tool_start()"]
  90ea8982_7d84_5e8f_4b5a_533f89fc7211["AsyncCallbackManager"]
  99e09f49_82fe_9b97_1a99_8b1db9974286 -->|defined in| 90ea8982_7d84_5e8f_4b5a_533f89fc7211
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0["on_tool_start()"]
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0 -->|calls| 99e09f49_82fe_9b97_1a99_8b1db9974286
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0["on_tool_start()"]
  99e09f49_82fe_9b97_1a99_8b1db9974286 -->|calls| a1fd3036_7b39_dbeb_ea97_f32d5d9822b0
  3a243d21_72d1_dca9_f7be_acbb482b9f86["ahandle_event()"]
  99e09f49_82fe_9b97_1a99_8b1db9974286 -->|calls| 3a243d21_72d1_dca9_f7be_acbb482b9f86
  style 99e09f49_82fe_9b97_1a99_8b1db9974286 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/callbacks/manager.py lines 1990–2035

    async def on_tool_start(
        self,
        serialized: dict[str, Any] | None,
        input_str: str,
        run_id: UUID | None = None,
        parent_run_id: UUID | None = None,
        **kwargs: Any,
    ) -> AsyncCallbackManagerForToolRun:
        """Run when the tool starts running.

        Args:
            serialized: The serialized tool.
            input_str: The input to the tool.
            run_id: The ID of the run.
            parent_run_id: The ID of the parent run.
            **kwargs: Additional keyword arguments.

        Returns:
            The async callback manager for the tool run.
        """
        if run_id is None:
            run_id = uuid7()

        await ahandle_event(
            self.handlers,
            "on_tool_start",
            "ignore_agent",
            serialized,
            input_str,
            run_id=run_id,
            parent_run_id=self.parent_run_id,
            tags=self.tags,
            metadata=self.metadata,
            **kwargs,
        )

        return AsyncCallbackManagerForToolRun(
            run_id=run_id,
            handlers=self.handlers,
            inheritable_handlers=self.inheritable_handlers,
            parent_run_id=self.parent_run_id,
            tags=self.tags,
            inheritable_tags=self.inheritable_tags,
            metadata=self.metadata,
            inheritable_metadata=self.inheritable_metadata,
        )