Tool execution succeeds but agent crashes due to serialization of unused tool variable

[Spixz]

Describe the bug
When my agent calls the tool, something try to serialize a variable from the tool that is not actually used, which causes the agent to crash. However, the tool itself is executed correctly.

File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/pydantic/type_adapter.py", line 572, in dump_python
 return self.serializer.to_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>

To Reproduce

from google.adk.agents import LlmAgent
from pymongo import MongoClient
import os


def store_events_in_db(events: list[dict]) -> str:
 """Insert a list of event dicts into MongoDB."""
 try:
 client = MongoClient(os.getenv("MONGO_URI"))
 db = client["ww1-france"]
 coll = db["events"]
 status = coll.insert_many(events)
 # coll.insert_many(events) crash too
 return "Events stored successfully."
 except Exception as e:
 return f"Error storing events: {e}"


root_agent = LlmAgent(
 name="StoreEventsAgent",
 model="gemini-2.0-flash",
 instruction="""You are given a variable `{events?}` containing a list of event dictionaries.

Call the tool `store_events_in_db` to insert `{events?}` into the database.
""",
 description="Store the given list of events in MongoDB",
 tools=[store_events_in_db],
 output_key="store_event_agent_output",
)


# mongo.Colleciton.insert_many() -> InsertManyResult:
# """Insert an iterable of documents.

# >>> result = db.test.insert_many([{'x': i} for i in range(2)])
# >>> result.inserted_ids
# [ObjectId('54f113fffba522406c9cc20e'), ObjectId('54f113fffba522406c9cc20f')]

The line causing the error is the following status = coll.insert_many(events).

• Create a MongoDB database and set the MONGO_URI environment variable.
• Run the agent using adk run web, then ask it the following:

add [{"title": "insert from chat 12"}] to events and insert it in the database.

(The same error appear when the agent is launch with runner.run)

The tool executes correctly, and the data is properly stored in the database, but the following error appears:

The main part of the error

 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 73, in app
 response = await f(request)
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 327, in app
 content = await serialize_response(
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 181, in serialize_response
 return field.serialize(
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/_compat.py", line 151, in serialize
 return self._type_adapter.dump_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/pydantic/type_adapter.py", line 572, in dump_python
 return self.serializer.to_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>
build graph

Complete logs

LLM Request:
-----------------------------------------------------------
System Instruction:
You are given a variable `` containing a list of event dictionaries.

Call the tool `store_events_in_db` to insert `` into the database.


You are an agent. Your internal name is "StoreEventsAgent".

 The description about you is "Store the given list of events in MongoDB"
-----------------------------------------------------------
Contents:
{"parts":[{"text":"add [{\"title\": \"insert from tchat 12\"}] to events and insert it in the database."}],"role":"user"}
-----------------------------------------------------------
Functions:
store_events_in_db: {'events': {'items': {'type': <Type.OBJECT: 'OBJECT'>}, 'type': <Type.ARRAY: 'ARRAY'>}} -> None
-----------------------------------------------------------

2025-05-30 16:37:21,123 - INFO - models.py:7118 - AFC is enabled with max remote calls: 10.
2025-05-30 16:37:22,027 - INFO - _client.py:1740 - HTTP Request: POST https://generativelanguage.googleapis.com/v1beta/models/gemini-2.0-flash:generateContent "HTTP/1.1 200 OK"
2025-05-30 16:37:22,030 - WARNING - types.py:4572 - Warning: there are non-text parts in the response: ['function_call'], returning concatenated text result from text parts. Check the full candidates.content.parts accessor to get the full model response.
2025-05-30 16:37:22,032 - INFO - google_llm.py:151 - 
LLM Response:
-----------------------------------------------------------
Text:
None
-----------------------------------------------------------
Function calls:
name: store_events_in_db, args: {'events': [{'title': 'insert from tchat 12'}]}
-----------------------------------------------------------
Raw response:
{"candidates":[{"content":{"parts":[{"function_call":{"args":{"events":[{"title":"insert from tchat 12"}]},"name":"store_events_in_db"}}],"role":"model"},"finish_reason":"STOP","avg_logprobs":-6.352143827825785e-6}],"model_version":"gemini-2.0-flash","usage_metadata":{"candidates_token_count":16,"candidates_tokens_details":[{"modality":"TEXT","token_count":16}],"prompt_token_count":109,"prompt_tokens_details":[{"modality":"TEXT","token_count":109}],"total_token_count":125},"automatic_function_calling_history":[]}
-----------------------------------------------------------

2025-05-30 16:37:22,033 - INFO - fast_api.py:705 - Generated event in agent run streaming: {"content":{"parts":[{"functionCall":{"id":"adk-fa88b514-8d96-4fdc-ae0a-7df90f257425","args":{"events":[{"title":"insert from tchat 12"}]},"name":"store_events_in_db"}}],"role":"model"},"usageMetadata":{"candidatesTokenCount":16,"candidatesTokensDetails":[{"modality":"TEXT","tokenCount":16}],"promptTokenCount":109,"promptTokensDetails":[{"modality":"TEXT","tokenCount":109}],"totalTokenCount":125},"invocationId":"e-9b8c827e-3fef-4e1a-96d9-e70f81e3c851","author":"StoreEventsAgent","actions":{"stateDelta":{},"artifactDelta":{},"requestedAuthConfigs":{}},"longRunningToolIds":[],"id":"FAZtPJCR","timestamp":1748615841.093331}
2025-05-30 16:37:26,575 - INFO - fast_api.py:705 - Generated event in agent run streaming: {"content":{"parts":[{"functionResponse":{"id":"adk-fa88b514-8d96-4fdc-ae0a-7df90f257425","name":"store_events_in_db","response":{"result":"Events stored successfully."}}}],"role":"user"},"invocationId":"e-9b8c827e-3fef-4e1a-96d9-e70f81e3c851","author":"StoreEventsAgent","actions":{"stateDelta":{},"artifactDelta":{},"requestedAuthConfigs":{}},"id":"qQsJvuYT","timestamp":1748615846.574966}
2025-05-30 16:37:26,616 - INFO - google_llm.py:85 - Sending out request, model: gemini-2.0-flash, backend: ml_dev, stream: False
2025-05-30 16:37:26,622 - ERROR - fast_api.py:708 - Error in event_generator: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>
Traceback (most recent call last):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/cli/fast_api.py", line 697, in event_generator
 async for event in runner.run_async(
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/runners.py", line 197, in run_async
 async for event in invocation_context.agent.run_async(invocation_context):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/agents/base_agent.py", line 147, in run_async
 async for event in self._run_async_impl(ctx):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/agents/llm_agent.py", line 278, in _run_async_impl
 async for event in self._llm_flow.run_async(ctx):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 279, in run_async
 async for event in self._run_one_step_async(invocation_context):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 305, in _run_one_step_async
 async for llm_response in self._call_llm_async(
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/flows/llm_flows/base_llm_flow.py", line 520, in _call_llm_async
 async for llm_response in llm.generate_content_async(
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/models/google_llm.py", line 91, in generate_content_async
 logger.info(_build_request_log(llm_request))
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/google/adk/models/google_llm.py", line 253, in _build_request_log
 content.model_dump_json(
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/pydantic/main.py", line 519, in model_dump_json
 return self.__pydantic_serializer__.to_json(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>
INFO: 127.0.0.1:56457 - "GET /apps/test_issue_sample/users/user/sessions/e81eea60-6a6d-4e3e-ad0f-a93069993f0c HTTP/1.1" 500 Internal Server Error
ERROR: Exception in ASGI application
Traceback (most recent call last):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
 result = await app( # type: ignore[func-returns-value]
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
 return await self.app(scope, receive, send)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/applications.py", line 1054, in __call__
 await super().__call__(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/applications.py", line 112, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 187, in __call__
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 165, in __call__
 await self.app(scope, receive, _send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
 await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 714, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 734, in app
 await route.handle(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 288, in handle
 await self.app(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 76, in app
 await wrap_app_handling_exceptions(app, request)(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 73, in app
 response = await f(request)
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 327, in app
 content = await serialize_response(
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 181, in serialize_response
 return field.serialize(
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/_compat.py", line 151, in serialize
 return self._type_adapter.dump_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/pydantic/type_adapter.py", line 572, in dump_python
 return self.serializer.to_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>
INFO: 127.0.0.1:56468 - "GET /debug/trace/session/e81eea60-6a6d-4e3e-ad0f-a93069993f0c HTTP/1.1" 200 OK
INFO: 127.0.0.1:56472 - "GET /apps/test_issue_sample/users/user/sessions/e81eea60-6a6d-4e3e-ad0f-a93069993f0c HTTP/1.1" 500 Internal Server Error
ERROR: Exception in ASGI application
Traceback (most recent call last):
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/h11_impl.py", line 403, in run_asgi
 result = await app( # type: ignore[func-returns-value]
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 60, in __call__
 return await self.app(scope, receive, send)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/applications.py", line 1054, in __call__
 await super().__call__(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/applications.py", line 112, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 187, in __call__
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 165, in __call__
 await self.app(scope, receive, _send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 62, in __call__
 await wrap_app_handling_exceptions(self.app, conn)(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 714, in __call__
 await self.middleware_stack(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 734, in app
 await route.handle(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 288, in handle
 await self.app(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 76, in app
 await wrap_app_handling_exceptions(app, request)(scope, receive, send)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 53, in wrapped_app
 raise exc
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/_exception_handler.py", line 42, in wrapped_app
 await app(scope, receive, sender)
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/starlette/routing.py", line 73, in app
 response = await f(request)
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 327, in app
 content = await serialize_response(
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 181, in serialize_response
 return field.serialize(
 ^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/fastapi/_compat.py", line 151, in serialize
 return self._type_adapter.dump_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/Users/cyril/projets/ww1_map/.venv/lib/python3.12/site-packages/pydantic/type_adapter.py", line 572, in dump_python
 return self.serializer.to_python(
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.PydanticSerializationError: Unable to serialize unknown type: <class 'bson.objectid.ObjectId'>
build graph
INFO: 127.0.0.1:56474 - "GET /apps/test_issue_sample/users/user/sessions/e81eea60-6a6d-4e3e-ad0f-a93069993f0c/events/qQsJvuYT/graph HTTP/1.1" 200 OK
INFO: 127.0.0.1:56473 - "GET /debug/trace/qQsJvuYT HTTP/1.1" 200 OK

Expected behavior
Should not crash.

Desktop

• OS: MacOS Sequioa 15.4.1
• Python version: 3.12.1
• ADK version: 1.1.1

Additional context
The most similar issue found : #878
Thanks for your work.

[Spixz]

I tried to skip the summarization but it didn't work:

def store_events_in_db(events: list[dict], tool_context: ToolContext) -> str:
 """Insert a list of event dicts into MongoDB."""
 try:
 coll.insert_many(events)
 tool_context.actions.skip_summarization = True
 return "Events stored successfully."
 except Exception as e:
 return f"Error storing events: {e}"

[jwiejulie]

Hi @Spixz and thanks to everyone who participated in this thread.

We're currently doing some housekeeping on our issue tracker. Given the rapid pace of development and the number of updates since this was last active, there's a good chance this issue has been resolved in a newer version. To help us keep our backlog focused on current issues, we are closing this as stale.

If you're still facing this problem, could you please update to the very latest version of the library and confirm the issue still exists? If it does, please comment here, and we will be happy to reopen this issue and investigate further.

Thanks for your contribution and understanding!