Can't load multiple mcp servers?

[zhh210]

The examples are all loading one mcp server but in practice it is very common to load multiple mcp servers. I tried extending the output from MCPToolset.from_server but not successful. Is there an example or recommended ways to get multiple mcp servers?

[boyangsvl]

You can create multiple toolset, each for one MCP server. E.g.

toolset1, exit_stack1 = await MCPToolset.from_server(...)
toolset2, exit_stack2 = await MCPToolset.from_server(...)

[zhh210]

ok, I found the error is due to one of the mcp servers mcp-alchemy:

"sqlalchemy": {
      "command": "/opt/conda/bin/uv",
      "args": ["--directory", "/home/jupyter/llms/mcp-alchemy", "run", "server.py"],
      "env": {
        "DB_URL": "trino://<user>:<password>@<host>:<port>/hive/db?session_properties={\"query_max_run_time\":\"1d\"}"
      }
    }

It worked with other agent frameworks (openai agents sdk, Claude, etc.) but fails on adk:

/opt/conda/lib/python3.10/site-packages/google/genai/_common.py:237: UserWarning: null is not a valid Type
  warnings.warn(f"{value} is not a valid {cls.__name__}")
Closing MCP server connection...
Cleanup complete.
An error occurred: 400 INVALID_ARGUMENT. {'error': {'code': 400, 'message': 'Invalid value at \'tools[0].function_declarations[46].parameters.properties[0].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[47].parameters.properties[0].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[47].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[48].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[49].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[50].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[50].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[51].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[51].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[52].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[53].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[53].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[53].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[54].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[54].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[54].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[55].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[55].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[56].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"\nInvalid value at \'tools[0].function_declarations[56].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"', 'status': 'INVALID_ARGUMENT', 'details': [{'@type': 'type.googleapis.com/google.rpc.BadRequest', 'fieldViolations': [{'field': 'tools[0].function_declarations[46].parameters.properties[0].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[46].parameters.properties[0].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[47].parameters.properties[0].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[47].parameters.properties[0].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[47].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[47].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[48].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[48].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[49].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[49].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[50].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[50].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[50].parameters.properties[3].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[50].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[51].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[51].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[51].parameters.properties[3].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[51].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[52].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[52].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[53].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[53].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[53].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[53].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[53].parameters.properties[3].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[53].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[54].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[54].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[54].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[54].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[54].parameters.properties[3].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[54].parameters.properties[3].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[55].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[55].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[55].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[55].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[56].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[56].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}, {'field': 'tools[0].function_declarations[56].parameters.properties[2].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[56].parameters.properties[2].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}]}]}}

[hangfei]

Does this only happen to mcp-alchemy? Or it happens to all situations when you have 2 MCP tools?
@zhh210

Could you share a minimal example to reproduce this error?

[zhh210]

I tried a bunch of mcps (filesystem, GitHub, slack, gitlab, etc.) and only seeing this error happening on mcp-alchemy. The error is likely due to the presence of slash/quote in the string of my DB_URL:

"DB_URL": "trino://<user>:<password>@<host>:<port>/hive/db?session_properties={\"query_max_run_time\":\"1d\"}"

To reproduce the error using a simple example, first launch a toy mysql service:

docker run --name mysql-container -e MYSQL_ROOT_PASSWORD=rootpassword -e MYSQL_USER=myuser -e MYSQL_PASSWORD=mypassword -e MYSQL_DATABASE=mydatabase -p 3306:3306 -d mysql:latest

docker exec -it mysql-container mysql -u myuser -p

Use the mysql mcp server as:

# ./adk_agent_samples/mcp_agent/agent.py
import asyncio
from dotenv import load_dotenv
from google.genai import types
from google.adk.agents.llm_agent import LlmAgent
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
from google.adk.artifacts.in_memory_artifact_service import (
    InMemoryArtifactService,
)  # Optional
from google.adk.tools.mcp_tool.mcp_toolset import (
    MCPToolset,
    SseServerParams,
    StdioServerParameters,
)

# Load environment variables from .env file in the parent directory
# Place this near the top, before using env vars like API keys
load_dotenv("../.env")


# --- Step 1: Import Tools from MCP Server ---
async def get_tools_async():
    """Gets tools from the File System MCP Server."""
    print("Attempting to connect to MCP Filesystem server...")
    tools, exit_stack = await MCPToolset.from_server(
        # Use StdioServerParameters for local process communication
        connection_params=StdioServerParameters(
            command="/opt/conda/bin/uv",  # Command to run the server
            args=["--directory", "/home/jupyter/llms/mcp-alchemy", "run", "server.py"],
            env={
                "DB_URL": "mysql+pymysql://myuser:mypassword@localhost:3306/mydatabase?connect_timeout=10000"
            },
        )
        # For remote servers, you would use SseServerParams instead:
        # connection_params=SseServerParams(url="http://remote-server:port/path", headers={...})
    )
    print("MCP Toolset created successfully.")
    # MCP requires maintaining a connection to the local MCP Server.
    # exit_stack manages the cleanup of this connection.
    return tools, exit_stack


# --- Step 2: Agent Definition ---
async def get_agent_async():
    """Creates an ADK Agent equipped with tools from the MCP Server."""
    tools, exit_stack = await get_tools_async()
    print(f"Fetched {len(tools)} tools from MCP server.")
    root_agent = LlmAgent(
        model="gemini-2.0-flash",  # Adjust model name if needed based on availability
        name="filesystem_assistant",
        instruction="Help user interact with the local filesystem using available tools.",
        tools=tools,  # Provide the MCP tools to the ADK agent
    )
    return root_agent, exit_stack


# --- Step 3: Main Execution Logic ---
async def async_main():
    session_service = InMemorySessionService()
    # Artifact service might not be needed for this example
    artifacts_service = InMemoryArtifactService()

    session = session_service.create_session(
        state={}, app_name="mcp_filesystem_app", user_id="user_fs"
    )

    # TODO: Change the query to be relevant to YOUR specified folder.
    # e.g., "list files in the 'documents' subfolder" or "read the file 'notes.txt'"
    query = "list files in the tests folder"
    print(f"User Query: '{query}'")
    content = types.Content(role="user", parts=[types.Part(text=query)])

    root_agent, exit_stack = await get_agent_async()

    runner = Runner(
        app_name="mcp_filesystem_app",
        agent=root_agent,
        artifact_service=artifacts_service,  # Optional
        session_service=session_service,
    )

    print("Running agent...")
    events_async = runner.run_async(
        session_id=session.id, user_id=session.user_id, new_message=content
    )

    async for event in events_async:
        print(f"Event received: {event}")

    # Crucial Cleanup: Ensure the MCP server process connection is closed.
    print("Closing MCP server connection...")
    await exit_stack.aclose()
    print("Cleanup complete.")


if __name__ == "__main__":
    try:
        asyncio.run(async_main())
    except Exception as e:
        print(f"An error occurred: {e}")

The MCP service connection is successful in adk but asking any questions (unrelated to the database) will get the error:

$ python toy_mcp.py 
User Query: 'list files in the tests folder'
Attempting to connect to MCP Filesystem server...
[04/14/25 05:56:08] INFO     Processing request of type ListToolsRequest                                       server.py:431
MCP Toolset created successfully.
Fetched 4 tools from MCP server.
Running agent...
/opt/conda/lib/python3.10/site-packages/google/genai/_common.py:237: UserWarning: null is not a valid Type
  warnings.warn(f"{value} is not a valid {cls.__name__}")
an error occurred during closing of asynchronous generator <async_generator object stdio_client at 0x7fa1341766c0>
asyncgen: <async_generator object stdio_client at 0x7fa1341766c0>
  + Exception Group Traceback (most recent call last):
  |   File "/opt/conda/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  | exceptiongroup.BaseExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/opt/conda/lib/python3.10/site-packages/mcp/client/stdio/__init__.py", line 173, in stdio_client
    |     yield read_stream, write_stream
    | GeneratorExit
    +------------------------------------

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/conda/lib/python3.10/site-packages/mcp/client/stdio/__init__.py", line 166, in stdio_client
    async with (
  File "/opt/conda/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 778, in __aexit__
    if self.cancel_scope.__exit__(type(exc), exc, exc.__traceback__):
  File "/opt/conda/lib/python3.10/site-packages/anyio/_backends/_asyncio.py", line 457, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
An error occurred: 400 INVALID_ARGUMENT. {'error': {'code': 400, 'message': 'Invalid value at \'tools[0].function_declarations[3].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"', 'status': 'INVALID_ARGUMENT', 'details': [{'@type': 'type.googleapis.com/google.rpc.BadRequest', 'fieldViolations': [{'field': 'tools[0].function_declarations[3].parameters.properties[1].value.any_of[1].type', 'description': 'Invalid value at \'tools[0].function_declarations[3].parameters.properties[1].value.any_of[1].type\' (type.googleapis.com/google.cloud.aiplatform.v1beta1.Type), "null"'}]}]}}