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
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0["on_tool_start()"]
  f2c19eb2_a092_16e7_b693_b7ae35a0bc8c["CallbackManager"]
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0 -->|defined in| f2c19eb2_a092_16e7_b693_b7ae35a0bc8c
  99e09f49_82fe_9b97_1a99_8b1db9974286["on_tool_start()"]
  99e09f49_82fe_9b97_1a99_8b1db9974286 -->|calls| a1fd3036_7b39_dbeb_ea97_f32d5d9822b0
  99e09f49_82fe_9b97_1a99_8b1db9974286["on_tool_start()"]
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0 -->|calls| 99e09f49_82fe_9b97_1a99_8b1db9974286
  8964b4e9_440e_18a7_2a15_a54a0b2b733c["handle_event()"]
  a1fd3036_7b39_dbeb_ea97_f32d5d9822b0 -->|calls| 8964b4e9_440e_18a7_2a15_a54a0b2b733c
  style a1fd3036_7b39_dbeb_ea97_f32d5d9822b0 fill:#6366f1,stroke:#818cf8,color:#fff

Relationship Graph

Source Code

libs/core/langchain_core/callbacks/manager.py lines 1458–1515

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

        Args:
            serialized: Serialized representation of the tool.
            input_str: The  input to the tool as a string.

                Non-string inputs are cast to strings.
            run_id: ID for the run.
            parent_run_id: The ID of the parent run.
            inputs: The original input to the tool if provided.

                Recommended for usage instead of input_str when the original input is
                needed.

                If provided, the inputs are expected to be formatted as a dict. The keys
                will correspond to the named-arguments in the tool.
            **kwargs: The keyword arguments to pass to the event handler

        Returns:
            The callback manager for the tool run.

        """
        if run_id is None:
            run_id = uuid7()

        handle_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,
            inputs=inputs,
            **kwargs,
        )

        return CallbackManagerForToolRun(
            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,
        )