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 +------------------------------------