Failed to parse JSONRPC message from server

[CrossLiu]

Using langchain to call playwright mcp, this issue not repro in Microsoft MCP @playwright/mcp@latest".

The code is as below:

from langchain_mcp_adapters.client import MultiServerMCPClient
from langchain_mcp_adapters.tools import load_mcp_tools
async def get_playwright_tools():

client = MultiServerMCPClient({
    "playwright": {
        "transport": "stdio",
        "command": "npx",
        "args": ["-y", "@executeautomation/playwright-mcp-server"]
    }
})

async with client.session("playwright") as session:
    tools = []
    try:
        tools = await load_mcp_tools(session)
        for tool in tools:
            print(f"     - {tool.name} - {tool.description} - type: {type(tool)}")
    except Exception as tool_error:
        print(f"   ✗ tool_error: {tool_error}")
        import traceback
        print(f"   error detail: {traceback.format_exc()}")
    
    if not tools:
        print("  ⚠ warning: no tools available!")

The error message:
Failed to parse JSONRPC message from server
Traceback (most recent call last):
File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\mcp\client\stdio_init_.py", line 155, in stdout_reader
message = types.JSONRPCMessage.model_validate_json(line)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\pydantic\main.py", line 766, in model_validate_json
return cls.pydantic_validator.validate_json(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for JSONRPCMessage
Invalid JSON: expected value at line 1 column 1 [type=json_invalid, input_value='Shutdown signal received', input_type=str]
For further information visit https://errors.pydantic.dev/2.12/v/json_invalid

• Exception Group Traceback (most recent call last):
  | File "c:\Users\Desktop\auto test code\AI_agent\langchain_demo\mcp\playwright_mcp_demo\playwright_mcp_绑定工具_.py", line 102, in
  | tools= asyncio.run(get_playwright_tools())
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\asyncio\runners.py", line 190, in run
  | return runner.run(main)
  | ^^^^^^^^^^^^^^^^
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\asyncio\runners.py", line 118, in run
  | return self.loop.run_until_complete(task)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\asyncio\base_events.py", line 654, in run_until_complete
  | return future.result()
  | ^^^^^^^^^^^^^^^
  | File "c:\Users\Desktop\auto test code\AI_agent\langchain_demo\mcp\playwright_mcp_demo\playwright_mcp_绑定工具.py", line 35, in get_playwright_tools
  | async with client.session("playwright") as session:
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\contextlib.py", line 217, in aexit
  | await anext(self.gen)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\langchain_mcp_adapters\client.py", line 123, in session
  | async with create_session(self.connections[server_name]) as session:
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\contextlib.py", line 217, in aexit
  | await anext(self.gen)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\langchain_mcp_adapters\sessions.py", line 403, in create_session
  | async with create_stdio_session(**params) as session:
  | File "C:\Users\JIAFLIU\AppData\Local\Programs\Python\Python311\Lib\contextlib.py", line 217, in aexit
  | await anext(self.gen)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\langchain_mcp_adapters\sessions.py", line 228, in create_stdio_session
  | async with (
  | File "C:\Users\AppData\Local\Programs\Python\Python311\Lib\contextlib.py", line 217, in aexit
  | await anext(self.gen)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\mcp\client\stdio_init.py", line 182, in stdio_client
  | async with (
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\anyio_backends_asyncio.py", line 781, in aexit
  | raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
  | Traceback (most recent call last):
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\mcp\client\stdio_init.py", line 155, in stdout_reader
  | message = types.JSONRPCMessage.model_validate_json(line)
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\pydantic\main.py", line 766, in model_validate_json
  | return cls.pydantic_validator.validate_json(
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  | pydantic_core.pydantic_core.ValidationError: 1 validation error for JSONRPCMessage
  Invalid JSON: expected value at line 1 column 1 [type=json_invalid, input_value='Shutdown signal received', input_type=str]
  For further information visit https://errors.pydantic.dev/2.12/v/json_invalid
  |
  | During handling of the above exception, another exception occurred:
  |
  | Traceback (most recent call last):
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\mcp\client\stdio_init.py", line 158, in stdout_reader
  | await read_stream_writer.send(exc)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\anyio\streams\memory.py", line 243, in send
  | self.send_nowait(item)
  | File "C:\Users\Desktop\auto test code\AI_agent\venv\Lib\site-packages\anyio\streams\memory.py", line 214, in send_nowait
  | raise BrokenResourceError
  | anyio.BrokenResourceError
  +------------------------------------