From 98780a98c6e316fb22435ff5ae0efbcb077a83fa Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Mon, 7 Apr 2025 10:46:29 -0400
Subject: [PATCH] core[patch]: add on_tool_error to
 _AstreamEventsCallbackHandler

---
 libs/core/langchain_core/runnables/schema.py  |  5 +++
 .../langchain_core/tracers/event_stream.py    | 35 +++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/libs/core/langchain_core/runnables/schema.py b/libs/core/langchain_core/runnables/schema.py
index 20ad580070a..e49f3c74949 100644
--- a/libs/core/langchain_core/runnables/schema.py
+++ b/libs/core/langchain_core/runnables/schema.py
@@ -23,6 +23,11 @@ class EventData(TypedDict, total=False):
     won't be known until the *END* of the Runnable when it has finished streaming
     its inputs.
     """
+    error: NotRequired[BaseException]
+    """The error that occurred during the execution of the Runnable.
+
+    This field is only available if the Runnable raised an exception.
+    """
     output: Any
     """The output of the Runnable that generated the event.
 
diff --git a/libs/core/langchain_core/tracers/event_stream.py b/libs/core/langchain_core/tracers/event_stream.py
index 7106a281ebd..b50b93b709f 100644
--- a/libs/core/langchain_core/tracers/event_stream.py
+++ b/libs/core/langchain_core/tracers/event_stream.py
@@ -627,6 +627,41 @@ class _AstreamEventsCallbackHandler(AsyncCallbackHandler, _StreamingCallbackHand
             "tool",
         )
 
+    async def on_tool_error(
+        self,
+        error: BaseException,
+        *,
+        run_id: UUID,
+        parent_run_id: Optional[UUID] = None,
+        tags: Optional[list[str]] = None,
+        **kwargs: Any,
+    ) -> None:
+        """Run when tool errors."""
+        run_info = self.run_map.pop(run_id)
+        if "inputs" not in run_info:
+            msg = (
+                f"Run ID {run_id} is a tool call and is expected to have "
+                f"inputs associated with it."
+            )
+            raise AssertionError(msg)
+        inputs = run_info["inputs"]
+
+        self._send(
+            {
+                "event": "on_tool_error",
+                "data": {
+                    "error": error,
+                    "input": inputs,
+                },
+                "run_id": str(run_id),
+                "name": run_info["name"],
+                "tags": run_info["tags"],
+                "metadata": run_info["metadata"],
+                "parent_ids": self._get_parent_ids(run_id),
+            },
+            "tool",
+        )
+
     async def on_tool_end(self, output: Any, *, run_id: UUID, **kwargs: Any) -> None:
         """End a trace for a tool run."""
         run_info = self.run_map.pop(run_id)