diff --git a/libs/langgraph/langgraph/prebuilt/tool_node.py b/libs/langgraph/langgraph/prebuilt/tool_node.py
index 099930fd5..0ed69a1e5 100644
--- a/libs/langgraph/langgraph/prebuilt/tool_node.py
+++ b/libs/langgraph/langgraph/prebuilt/tool_node.py
@@ -1,5 +1,4 @@
 import asyncio
-import json
 from typing import Any, Callable, Dict, Literal, Optional, Sequence, Union
 
 from langchain_core.messages import AIMessage, AnyMessage, ToolCall, ToolMessage
@@ -11,20 +10,11 @@ from langchain_core.tools import tool as create_tool
 from langgraph.utils import RunnableCallable
 
 
-def str_output(output: Any) -> str:
-    if isinstance(output, str):
-        return output
-    else:
-        try:
-            return json.dumps(output)
-        except Exception:
-            return str(output)
-
-
 class ToolNode(RunnableCallable):
-    """A node that runs the tools requested in the last AIMessage. It can be used
-    either in StateGraph with a "messages" key or in MessageGraph. If multiple
-    tool calls are requested, they will be run in parallel. The output will be
+    """A node that runs the tools called in the last AIMessage.
+
+    It can be used either in StateGraph with a "messages" key or in MessageGraph. If
+    multiple tool calls are requested, they will be run in parallel. The output will be
     a list of ToolMessages, one for each tool call.
 
     The `ToolNode` is roughly analogous to:
@@ -79,14 +69,13 @@ class ToolNode(RunnableCallable):
 
         def run_one(call: ToolCall):
             try:
-                output = self.tools_by_name[call["name"]].invoke(call["args"], config)
+                input = {**call, **{"type": "tool_call"}}
+                return self.tools_by_name[call["name"]].invoke(input, config)
             except Exception as e:
                 if not self.handle_tool_errors:
                     raise e
-                output = f"Error: {repr(e)}\n Please fix your mistakes."
-            return ToolMessage(
-                content=str_output(output), name=call["name"], tool_call_id=call["id"]
-            )
+                content = f"Error: {repr(e)}\n Please fix your mistakes."
+                return ToolMessage(content, name=call["name"], tool_call_id=call["id"])
 
         with get_executor_for_config(config) as executor:
             outputs = [*executor.map(run_one, message.tool_calls)]
@@ -112,16 +101,13 @@ class ToolNode(RunnableCallable):
 
         async def run_one(call: ToolCall):
             try:
-                output = await self.tools_by_name[call["name"]].ainvoke(
-                    call["args"], config
-                )
+                input = {**call, **{"type": "tool_call"}}
+                return await self.tools_by_name[call["name"]].ainvoke(input, config)
             except Exception as e:
                 if not self.handle_tool_errors:
                     raise e
-                output = f"Error: {repr(e)}\n Please fix your mistakes."
-            return ToolMessage(
-                content=str_output(output), name=call["name"], tool_call_id=call["id"]
-            )
+                content = f"Error: {repr(e)}\n Please fix your mistakes."
+                return ToolMessage(content, name=call["name"], tool_call_id=call["id"])
 
         outputs = await asyncio.gather(*(run_one(call) for call in message.tool_calls))
         if output_type == "list":
diff --git a/libs/langgraph/poetry.lock b/libs/langgraph/poetry.lock
index 30297cc8d..f068e1405 100644
--- a/libs/langgraph/poetry.lock
+++ b/libs/langgraph/poetry.lock
@@ -1746,13 +1746,13 @@ langchain-core = ">=0.2.2rc1,<0.3"
 
 [[package]]
 name = "langchain-core"
-version = "0.2.16"
+version = "0.2.19"
 description = "Building applications with LLMs through composability"
 optional = false
 python-versions = "<4.0,>=3.8.1"
 files = [
-    {file = "langchain_core-0.2.16-py3-none-any.whl", hash = "sha256:68dd6fbdd8d704e124ee14c39d0b0dcf38a47bb32234328b63ad2e98385b1c80"},
-    {file = "langchain_core-0.2.16.tar.gz", hash = "sha256:cc03083e059bff86ca3e6ba60097f91d7765a929edd04eb226bb20c208447caf"},
+    {file = "langchain_core-0.2.19-py3-none-any.whl", hash = "sha256:5b3cd34395be274c89e822c84f0e03c4da14168c177a83921c5b9414ac7a0651"},
+    {file = "langchain_core-0.2.19.tar.gz", hash = "sha256:13043a83e5c9ab58b9f5ce2a56896e7e88b752e8891b2958960a98e71801471e"},
 ]
 
 [package.dependencies]
@@ -4130,4 +4130,4 @@ test = ["big-O", "importlib-resources", "jaraco.functools", "jaraco.itertools",
 [metadata]
 lock-version = "2.0"
 python-versions = ">=3.9.0,<4.0"
-content-hash = "19250230952cb11ee6b5c820ae0a2b589ce520a59e0723204dcee0c46c3b739e"
+content-hash = "170eaa0e542a02d5f2fb0d42d1f04c5d010bd3735a44b927b28e6b742c689eb0"
diff --git a/libs/langgraph/pyproject.toml b/libs/langgraph/pyproject.toml
index 86d2401cf..1d0732ca5 100644
--- a/libs/langgraph/pyproject.toml
+++ b/libs/langgraph/pyproject.toml
@@ -9,7 +9,7 @@ repository = "https://www.github.com/langchain-ai/langgraph"
 
 [tool.poetry.dependencies]
 python = ">=3.9.0,<4.0"
-langchain-core = ">=0.2.15,<0.3"
+langchain-core = ">=0.2.19,<0.3"
 
 
 [tool.poetry.group.dev.dependencies]
@@ -61,7 +61,7 @@ omit = ["tests/*"]
 [tool.pytest-watcher]
 now = true
 delay = 0.1
-runner_args = ["-x", "--ff", "-vv", "--snapshot-update"]
+runner_args = ["--ff", "-vv", "--snapshot-update"]
 patterns = ["*.py"]
 
 [build-system]
diff --git a/libs/langgraph/tests/__snapshots__/test_pregel.ambr b/libs/langgraph/tests/__snapshots__/test_pregel.ambr
index bb751932f..28b27a82c 100644
--- a/libs/langgraph/tests/__snapshots__/test_pregel.ambr
+++ b/libs/langgraph/tests/__snapshots__/test_pregel.ambr
@@ -629,10 +629,10 @@
   '''
 # ---
 # name: test_message_graph
-  '{"title": "LangGraphOutput", "type": "array", "items": {"anyOf": [{"$ref": "#/definitions/AIMessage"}, {"$ref": "#/definitions/HumanMessage"}, {"$ref": "#/definitions/ChatMessage"}, {"$ref": "#/definitions/SystemMessage"}, {"$ref": "#/definitions/FunctionMessage"}, {"$ref": "#/definitions/ToolMessage"}]}, "definitions": {"ToolCall": {"title": "ToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "object"}, "id": {"title": "Id", "type": "string"}, "type": {"title": "Type", "enum": ["tool_call"], "type": "string"}}, "required": ["name", "args", "id"]}, "InvalidToolCall": {"title": "InvalidToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "string"}, "id": {"title": "Id", "type": "string"}, "error": {"title": "Error", "type": "string"}, "type": {"title": "Type", "enum": ["invalid_tool_call"], "type": "string"}}, "required": ["name", "args", "id", "error"]}, "UsageMetadata": {"title": "UsageMetadata", "type": "object", "properties": {"input_tokens": {"title": "Input Tokens", "type": "integer"}, "output_tokens": {"title": "Output Tokens", "type": "integer"}, "total_tokens": {"title": "Total Tokens", "type": "integer"}}, "required": ["input_tokens", "output_tokens", "total_tokens"]}, "AIMessage": {"title": "AIMessage", "description": "Message from an AI.\\n\\nAIMessage is returned from a chat model as a response to a prompt.\\n\\nThis message represents the output of the model and consists of both\\nthe raw output as returned by the model together standardized fields\\n(e.g., tool calls, usage metadata) added by the LangChain framework.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "ai", "enum": ["ai"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}, "tool_calls": {"title": "Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/ToolCall"}}, "invalid_tool_calls": {"title": "Invalid Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/InvalidToolCall"}}, "usage_metadata": {"$ref": "#/definitions/UsageMetadata"}}, "required": ["content"]}, "HumanMessage": {"title": "HumanMessage", "description": "Message from a human.\\n\\nHumanMessages are messages that are passed in from a human to the model.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Instantiate a chat model and invoke it with the messages\\n        model = ...\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "human", "enum": ["human"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}}, "required": ["content"]}, "ChatMessage": {"title": "ChatMessage", "description": "Message that can be assigned an arbitrary speaker (i.e. role).", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "chat", "enum": ["chat"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "role": {"title": "Role", "type": "string"}}, "required": ["content", "role"]}, "SystemMessage": {"title": "SystemMessage", "description": "Message for priming AI behavior.\\n\\nThe system message is usually passed in as the first of a sequence\\nof input messages.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Define a chat model and invoke it with the messages\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "system", "enum": ["system"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content"]}, "FunctionMessage": {"title": "FunctionMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nFunctionMessage are an older version of the ToolMessage schema, and\\ndo not contain the tool_call_id field.\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "function", "enum": ["function"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content", "name"]}, "ToolMessage": {"title": "ToolMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nToolMessages contain the result of a tool invocation. Typically, the result\\nis encoded inside the `content` field.\\n\\nExample: A ToolMessage representing a result of 42 from a tool call with id\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        ToolMessage(content=\'42\', tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\')\\n\\nExample: A ToolMessage where only part of the tool output is sent to the model\\n    and the full output is passed in to raw_output.\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        tool_output = {\\n            \\"stdout\\": \\"From the graph we can see that the correlation between x and y is ...\\",\\n            \\"stderr\\": None,\\n            \\"artifacts\\": {\\"type\\": \\"image\\", \\"base64_data\\": \\"/9j/4gIcSU...\\"},\\n        }\\n\\n        ToolMessage(\\n            content=tool_output[\\"stdout\\"],\\n            raw_output=tool_output,\\n            tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\',\\n        )\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "tool", "enum": ["tool"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "tool_call_id": {"title": "Tool Call Id", "type": "string"}, "raw_output": {"title": "Raw Output"}}, "required": ["content", "tool_call_id"]}}}'
+  '{"title": "LangGraphOutput", "type": "array", "items": {"anyOf": [{"$ref": "#/definitions/AIMessage"}, {"$ref": "#/definitions/HumanMessage"}, {"$ref": "#/definitions/ChatMessage"}, {"$ref": "#/definitions/SystemMessage"}, {"$ref": "#/definitions/FunctionMessage"}, {"$ref": "#/definitions/ToolMessage"}]}, "definitions": {"ToolCall": {"title": "ToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "object"}, "id": {"title": "Id", "type": "string"}, "type": {"title": "Type", "enum": ["tool_call"], "type": "string"}}, "required": ["name", "args", "id"]}, "InvalidToolCall": {"title": "InvalidToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "string"}, "id": {"title": "Id", "type": "string"}, "error": {"title": "Error", "type": "string"}, "type": {"title": "Type", "enum": ["invalid_tool_call"], "type": "string"}}, "required": ["name", "args", "id", "error"]}, "UsageMetadata": {"title": "UsageMetadata", "type": "object", "properties": {"input_tokens": {"title": "Input Tokens", "type": "integer"}, "output_tokens": {"title": "Output Tokens", "type": "integer"}, "total_tokens": {"title": "Total Tokens", "type": "integer"}}, "required": ["input_tokens", "output_tokens", "total_tokens"]}, "AIMessage": {"title": "AIMessage", "description": "Message from an AI.\\n\\nAIMessage is returned from a chat model as a response to a prompt.\\n\\nThis message represents the output of the model and consists of both\\nthe raw output as returned by the model together standardized fields\\n(e.g., tool calls, usage metadata) added by the LangChain framework.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "ai", "enum": ["ai"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}, "tool_calls": {"title": "Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/ToolCall"}}, "invalid_tool_calls": {"title": "Invalid Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/InvalidToolCall"}}, "usage_metadata": {"$ref": "#/definitions/UsageMetadata"}}, "required": ["content"]}, "HumanMessage": {"title": "HumanMessage", "description": "Message from a human.\\n\\nHumanMessages are messages that are passed in from a human to the model.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Instantiate a chat model and invoke it with the messages\\n        model = ...\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "human", "enum": ["human"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}}, "required": ["content"]}, "ChatMessage": {"title": "ChatMessage", "description": "Message that can be assigned an arbitrary speaker (i.e. role).", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "chat", "enum": ["chat"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "role": {"title": "Role", "type": "string"}}, "required": ["content", "role"]}, "SystemMessage": {"title": "SystemMessage", "description": "Message for priming AI behavior.\\n\\nThe system message is usually passed in as the first of a sequence\\nof input messages.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Define a chat model and invoke it with the messages\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "system", "enum": ["system"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content"]}, "FunctionMessage": {"title": "FunctionMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nFunctionMessage are an older version of the ToolMessage schema, and\\ndo not contain the tool_call_id field.\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "function", "enum": ["function"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content", "name"]}, "ToolMessage": {"title": "ToolMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nToolMessages contain the result of a tool invocation. Typically, the result\\nis encoded inside the `content` field.\\n\\nExample: A ToolMessage representing a result of 42 from a tool call with id\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        ToolMessage(content=\'42\', tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\')\\n\\n\\nExample: A ToolMessage where only part of the tool output is sent to the model\\n    and the full output is passed in to artifact.\\n\\n    .. versionadded:: 0.2.17\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        tool_output = {\\n            \\"stdout\\": \\"From the graph we can see that the correlation between x and y is ...\\",\\n            \\"stderr\\": None,\\n            \\"artifacts\\": {\\"type\\": \\"image\\", \\"base64_data\\": \\"/9j/4gIcSU...\\"},\\n        }\\n\\n        ToolMessage(\\n            content=tool_output[\\"stdout\\"],\\n            artifact=tool_output,\\n            tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\',\\n        )\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "tool", "enum": ["tool"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "tool_call_id": {"title": "Tool Call Id", "type": "string"}, "artifact": {"title": "Artifact"}}, "required": ["content", "tool_call_id"]}}}'
 # ---
 # name: test_message_graph.1
-  '{"title": "LangGraphOutput", "type": "array", "items": {"anyOf": [{"$ref": "#/definitions/AIMessage"}, {"$ref": "#/definitions/HumanMessage"}, {"$ref": "#/definitions/ChatMessage"}, {"$ref": "#/definitions/SystemMessage"}, {"$ref": "#/definitions/FunctionMessage"}, {"$ref": "#/definitions/ToolMessage"}]}, "definitions": {"ToolCall": {"title": "ToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "object"}, "id": {"title": "Id", "type": "string"}, "type": {"title": "Type", "enum": ["tool_call"], "type": "string"}}, "required": ["name", "args", "id"]}, "InvalidToolCall": {"title": "InvalidToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "string"}, "id": {"title": "Id", "type": "string"}, "error": {"title": "Error", "type": "string"}, "type": {"title": "Type", "enum": ["invalid_tool_call"], "type": "string"}}, "required": ["name", "args", "id", "error"]}, "UsageMetadata": {"title": "UsageMetadata", "type": "object", "properties": {"input_tokens": {"title": "Input Tokens", "type": "integer"}, "output_tokens": {"title": "Output Tokens", "type": "integer"}, "total_tokens": {"title": "Total Tokens", "type": "integer"}}, "required": ["input_tokens", "output_tokens", "total_tokens"]}, "AIMessage": {"title": "AIMessage", "description": "Message from an AI.\\n\\nAIMessage is returned from a chat model as a response to a prompt.\\n\\nThis message represents the output of the model and consists of both\\nthe raw output as returned by the model together standardized fields\\n(e.g., tool calls, usage metadata) added by the LangChain framework.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "ai", "enum": ["ai"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}, "tool_calls": {"title": "Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/ToolCall"}}, "invalid_tool_calls": {"title": "Invalid Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/InvalidToolCall"}}, "usage_metadata": {"$ref": "#/definitions/UsageMetadata"}}, "required": ["content"]}, "HumanMessage": {"title": "HumanMessage", "description": "Message from a human.\\n\\nHumanMessages are messages that are passed in from a human to the model.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Instantiate a chat model and invoke it with the messages\\n        model = ...\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "human", "enum": ["human"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}}, "required": ["content"]}, "ChatMessage": {"title": "ChatMessage", "description": "Message that can be assigned an arbitrary speaker (i.e. role).", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "chat", "enum": ["chat"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "role": {"title": "Role", "type": "string"}}, "required": ["content", "role"]}, "SystemMessage": {"title": "SystemMessage", "description": "Message for priming AI behavior.\\n\\nThe system message is usually passed in as the first of a sequence\\nof input messages.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Define a chat model and invoke it with the messages\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "system", "enum": ["system"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content"]}, "FunctionMessage": {"title": "FunctionMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nFunctionMessage are an older version of the ToolMessage schema, and\\ndo not contain the tool_call_id field.\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "function", "enum": ["function"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content", "name"]}, "ToolMessage": {"title": "ToolMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nToolMessages contain the result of a tool invocation. Typically, the result\\nis encoded inside the `content` field.\\n\\nExample: A ToolMessage representing a result of 42 from a tool call with id\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        ToolMessage(content=\'42\', tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\')\\n\\nExample: A ToolMessage where only part of the tool output is sent to the model\\n    and the full output is passed in to raw_output.\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        tool_output = {\\n            \\"stdout\\": \\"From the graph we can see that the correlation between x and y is ...\\",\\n            \\"stderr\\": None,\\n            \\"artifacts\\": {\\"type\\": \\"image\\", \\"base64_data\\": \\"/9j/4gIcSU...\\"},\\n        }\\n\\n        ToolMessage(\\n            content=tool_output[\\"stdout\\"],\\n            raw_output=tool_output,\\n            tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\',\\n        )\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "tool", "enum": ["tool"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "tool_call_id": {"title": "Tool Call Id", "type": "string"}, "raw_output": {"title": "Raw Output"}}, "required": ["content", "tool_call_id"]}}}'
+  '{"title": "LangGraphOutput", "type": "array", "items": {"anyOf": [{"$ref": "#/definitions/AIMessage"}, {"$ref": "#/definitions/HumanMessage"}, {"$ref": "#/definitions/ChatMessage"}, {"$ref": "#/definitions/SystemMessage"}, {"$ref": "#/definitions/FunctionMessage"}, {"$ref": "#/definitions/ToolMessage"}]}, "definitions": {"ToolCall": {"title": "ToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "object"}, "id": {"title": "Id", "type": "string"}, "type": {"title": "Type", "enum": ["tool_call"], "type": "string"}}, "required": ["name", "args", "id"]}, "InvalidToolCall": {"title": "InvalidToolCall", "type": "object", "properties": {"name": {"title": "Name", "type": "string"}, "args": {"title": "Args", "type": "string"}, "id": {"title": "Id", "type": "string"}, "error": {"title": "Error", "type": "string"}, "type": {"title": "Type", "enum": ["invalid_tool_call"], "type": "string"}}, "required": ["name", "args", "id", "error"]}, "UsageMetadata": {"title": "UsageMetadata", "type": "object", "properties": {"input_tokens": {"title": "Input Tokens", "type": "integer"}, "output_tokens": {"title": "Output Tokens", "type": "integer"}, "total_tokens": {"title": "Total Tokens", "type": "integer"}}, "required": ["input_tokens", "output_tokens", "total_tokens"]}, "AIMessage": {"title": "AIMessage", "description": "Message from an AI.\\n\\nAIMessage is returned from a chat model as a response to a prompt.\\n\\nThis message represents the output of the model and consists of both\\nthe raw output as returned by the model together standardized fields\\n(e.g., tool calls, usage metadata) added by the LangChain framework.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "ai", "enum": ["ai"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}, "tool_calls": {"title": "Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/ToolCall"}}, "invalid_tool_calls": {"title": "Invalid Tool Calls", "default": [], "type": "array", "items": {"$ref": "#/definitions/InvalidToolCall"}}, "usage_metadata": {"$ref": "#/definitions/UsageMetadata"}}, "required": ["content"]}, "HumanMessage": {"title": "HumanMessage", "description": "Message from a human.\\n\\nHumanMessages are messages that are passed in from a human to the model.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Instantiate a chat model and invoke it with the messages\\n        model = ...\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "human", "enum": ["human"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "example": {"title": "Example", "default": false, "type": "boolean"}}, "required": ["content"]}, "ChatMessage": {"title": "ChatMessage", "description": "Message that can be assigned an arbitrary speaker (i.e. role).", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "chat", "enum": ["chat"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "role": {"title": "Role", "type": "string"}}, "required": ["content", "role"]}, "SystemMessage": {"title": "SystemMessage", "description": "Message for priming AI behavior.\\n\\nThe system message is usually passed in as the first of a sequence\\nof input messages.\\n\\nExample:\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import HumanMessage, SystemMessage\\n\\n        messages = [\\n            SystemMessage(\\n                content=\\"You are a helpful assistant! Your name is Bob.\\"\\n            ),\\n            HumanMessage(\\n                content=\\"What is your name?\\"\\n            )\\n        ]\\n\\n        # Define a chat model and invoke it with the messages\\n        print(model.invoke(messages))", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "system", "enum": ["system"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content"]}, "FunctionMessage": {"title": "FunctionMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nFunctionMessage are an older version of the ToolMessage schema, and\\ndo not contain the tool_call_id field.\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "function", "enum": ["function"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}}, "required": ["content", "name"]}, "ToolMessage": {"title": "ToolMessage", "description": "Message for passing the result of executing a tool back to a model.\\n\\nToolMessages contain the result of a tool invocation. Typically, the result\\nis encoded inside the `content` field.\\n\\nExample: A ToolMessage representing a result of 42 from a tool call with id\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        ToolMessage(content=\'42\', tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\')\\n\\n\\nExample: A ToolMessage where only part of the tool output is sent to the model\\n    and the full output is passed in to artifact.\\n\\n    .. versionadded:: 0.2.17\\n\\n    .. code-block:: python\\n\\n        from langchain_core.messages import ToolMessage\\n\\n        tool_output = {\\n            \\"stdout\\": \\"From the graph we can see that the correlation between x and y is ...\\",\\n            \\"stderr\\": None,\\n            \\"artifacts\\": {\\"type\\": \\"image\\", \\"base64_data\\": \\"/9j/4gIcSU...\\"},\\n        }\\n\\n        ToolMessage(\\n            content=tool_output[\\"stdout\\"],\\n            artifact=tool_output,\\n            tool_call_id=\'call_Jja7J89XsjrOLA5r!MEOW!SL\',\\n        )\\n\\nThe tool_call_id field is used to associate the tool call request with the\\ntool call response. This is useful in situations where a chat model is able\\nto request multiple tool calls in parallel.", "type": "object", "properties": {"content": {"title": "Content", "anyOf": [{"type": "string"}, {"type": "array", "items": {"anyOf": [{"type": "string"}, {"type": "object"}]}}]}, "additional_kwargs": {"title": "Additional Kwargs", "type": "object"}, "response_metadata": {"title": "Response Metadata", "type": "object"}, "type": {"title": "Type", "default": "tool", "enum": ["tool"], "type": "string"}, "name": {"title": "Name", "type": "string"}, "id": {"title": "Id", "type": "string"}, "tool_call_id": {"title": "Tool Call Id", "type": "string"}, "artifact": {"title": "Artifact"}}, "required": ["content", "tool_call_id"]}}}'
 # ---
 # name: test_message_graph.2
   '''
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index 0c1ef98b2..66d1b26fb 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -3143,6 +3143,7 @@ Some examples of past conversations:
                         "name": "search_api",
                         "args": {"query": "query"},
                         "id": "tool_call123",
+                        "type": "tool_call",
                     }
                 ],
             ),
@@ -3154,7 +3155,7 @@ Some examples of past conversations:
             ),
             AIMessage(content="answer", id=AnyStr()),
         ]
-        assert app.invoke(
+        actual = app.invoke(
             {"messages": "what is weather in sf"},
             {
                 "configurable": {
@@ -3162,7 +3163,9 @@ Some examples of past conversations:
                     "expected_examples": [],
                 },
             },
-        ) == {"messages": first_messages}
+        )
+        expected = {"messages": first_messages}
+        assert actual == expected
 
         # get first checkpoint
         chkpnt_tuple_1 = saver.get_tuple({"configurable": {"thread_id": "1"}})
@@ -3193,6 +3196,7 @@ Some examples of past conversations:
                         "name": "search_api",
                         "args": {"query": "query"},
                         "id": "tool_call123",
+                        "type": "tool_call",
                     }
                 ],
             ),
@@ -3252,6 +3256,7 @@ Some examples of past conversations:
                             "name": "search_api",
                             "args": {"query": "query"},
                             "id": "tool_call123",
+                            "type": "tool_call",
                         }
                     ],
                 ),