When using the MCP tool under langgraph_supervisor with LangGraph API Server, there are 1. Repeat loop bug; 2. Blocking in calling the tool #249
Description
When I use MCP on a sub-agent under the supervisor multi-agent and test it with langgraph-cli, I find that 1. a repeated loop; 2. a blocking when calling a method. However, when running it locally, the results are returned normally.
# graph.py
from contextlib import asynccontextmanager
from langchain_mcp_adapters.client import MultiServerMCPClient
from langgraph.prebuilt import create_react_agent
from langchain_openai import ChatOpenAI
from langgraph_supervisor import create_supervisor
from langchain.chat_models import init_chat_model
async def make_graph():
MCP_DIR = r"xxxxxxxx"
client = MultiServerMCPClient(
{
"desktop-commander": {
"command": "npx",
"args": [
"--no-install",
"--yes",
"@wonderwhy-er/desktop-commander",
"serve",
"--no-onboarding"
],
"transport": "stdio",
"cwd": MCP_DIR
},
"ssh-mcp-server": {
"command": "npx",
"args": [
"--no-install",
"-y",
"@fangjunjie/ssh-mcp-server",
"--host", "xxxxxx",
"--port", "22",
"--username", "xxxxx",
"--password", "xxxxx",
],
"transport": "stdio",
"cwd": MCP_DIR
}
}
)
tools = await client.get_tools()
Filesystem_tools = [t for t in tools if t.name in {
'read_file', 'read_multiple_files', 'write_file', 'create_directory',
'list_directory', 'move_file', 'get_file_info', 'edit_block',
'start_search', 'stop_search', 'list_searches', 'get_more_search_results'
}]
Terminal_tools = [t for t in tools if t.name in {
'start_process', 'read_process_output', 'interact_with_process',
'force_terminate', 'list_sessions', 'list_processes', 'kill_process'
}]
SSH_tools = [t for t in tools if t.name in {
'execute-command', 'upload', 'download', 'list-servers'
}]
llm = init_chat_model(
model="qwen3:14b",
model_provider="ollama",
base_url="http://localhost:11434",
)
filesystem_agent = create_react_agent(
llm,
tools=Filesystem_tools,
prompt="""xxxxxx""",
name="filesystem_agent",
)
terminal_agent = create_react_agent(
llm,
tools=Terminal_tools,
prompt="""xxxxxx""",
name="terminal_agent",
)
ssh_agent = create_react_agent(
llm,
tools=SSH_tools,
prompt="""xxxxxx""",
name="ssh_agent",
)
agent = create_supervisor(
model=llm,
agents=[filesystem_agent, terminal_agent, ssh_agent],
prompt='xxxxxx',
add_handoff_back_messages=True,
output_mode="full_history",
).compile()
return agent
if __name__ == '__main__':
# 'langgraph dev --allow-blocking'
import asyncio
async def main():
graph = await make_graph()
result = await graph.ainvoke(
input={"messages": [{"role": "user", "content": r"SSH remote connection to the server and check the disk space"}]}
)
print("Agent Invocation Result:")
print(result)
asyncio.run(main())
The test cases are：List the files/folders under "/PATH". The filesystem_agent will always ask "I'm here to help with file system tasks. What would you like to do?" The same prompt will work fine when running locally.
