[Python] Postgresql MCP server not running. Tool showing error

Here is the code I am running for mcp-server on cursor -

from contextlib import asynccontextmanager
from collections.abc import AsyncIterator
from dataclasses import dataclass

import asyncpg
from mcp.server.fastmcp import FastMCP, Context

# Async PostgreSQL wrapper using asyncpg
class Database:
def __init__(self, pool: asyncpg.Pool):
self.pool = pool

@classmethod
async def connect(cls) -> "Database":
pool = await asyncpg.create_pool(
user="postgres",
password="rohan",
database="company",
host="localhost",
port=5432,
)
return cls(pool)

async def disconnect(self):
await self.pool.close()

async def query(self, query: str) -> list:
async with self.pool.acquire() as conn:
try:
return await conn.fetch(query)
except Exception as e:
print(f"Query error: {e}")
return []

async def fetch_schema(self) -> list:
query = """
SELECT table_name FROM information_schema.tables
WHERE table_schema = 'public'
"""
return await self.query(query)


@dataclass
class AppContext:
db: Database


@asynccontextmanager
async def app_lifespan(server: FastMCP) -> AsyncIterator[AppContext]:
db = await Database.connect()
try:
yield AppContext(db=db)
finally:
await db.disconnect()


mcp = FastMCP("PostgresMCPServer", lifespan=app_lifespan)

@mcp.tool("fetch_schema")
async def fetch_schema(ctx: Context) -> str:
db = ctx.request_context.lifespan_context.db
schema = await db.fetch_schema()
return str([record["table_name"] for record in schema])


@mcp.tool("fetch_all_tables")
async def fetch_all_tables(ctx: Context) -> str:
db = ctx.request_context.lifespan_context.db
query = "SELECT * FROM information_schema.tables WHERE table_schema='public'"
tables = await db.query(query)
return str(tables)


@mcp.tool("run_query")
async def run_query(ctx: Context, query: str) -> str:
db = ctx.request_context.lifespan_context.db
result = await db.query(query)
return str(result)

if __name__ == "__main__":
# Initialize and run the server
mcp.run()


Here are the libraries i have installed and they are showing up on pyproject.toml file as well -

mcp
httpx
mcp[cli]
asyncpg


Here is how i am adding the mcp to use as a tool -

"PostgresMCPServer": {
"command": "uv",
"args": [
"run",
"--with",
"mcp[cli]",
"mcp",
"run",
"C:/mylocalpath/server.py"
]
}


When I run the server.py, the tool shows error on cursor as well as claude desktop. Here are some error logs from claude -

2025-07-21T12:05:43.760Z [PostgresMCPServer] [info] Initializing server... { metadata: undefined }
2025-07-21T12:05:43.801Z [PostgresMCPServer] [info] Using MCP server command: C:\Users\Rohan\AppData\Local\com.Langflow\uv\uv.exe with args and path: {
metadata: {
args: [
'run',
'--with',
'mcp[cli]',
'mcp',
'run',
'C:/Users/Rohan/Desktop/MCP_newProjects/postgress-mcp/server.py',
[length]: 6
],
paths: [
'C:\\Program Files\\nodejs',
'C:\\Python312\\Scripts\\',
'C:\\Python312\\',
'C:\\WINDOWS\\system32',
'C:\\WINDOWS',
'C:\\WINDOWS\\System32\\Wbem',
'C:\\WINDOWS\\System32\\WindowsPowerShell\\v1.0\\',
'C:\\WINDOWS\\System32\\OpenSSH\\',
'C:\\Program Files\\nodejs\\',
'C:\\ProgramData\\chocolatey\\bin',
'C:\\Terraform',
'C:\\Program Files\\Amazon\\AWSCLIV2\\',
'C:\\Program Files\\PuTTY\\',
'C:\\Program Files\\Git\\cmd',
'C:\\ProgramData\\miniconda3\\Library\\bin\\conda.bat',
'C:\\ProgramData\\miniconda3\\Scripts\\conda.exe',
'C:\\ProgramData\\miniconda3\\condabin\\conda.bat',
'C:\\ProgramData\\miniconda3',
'C:\\ProgramData\\miniconda3\\Library\\bin',
'C:\\ProgramData\\miniconda3\\Scripts',
'',
'c:\\Users\\Rohan\\AppData\\Local\\Programs\\cursor\\resources\\app\\bin',
'c:\\Users\\Rohan\\AppData\\Local\\Programs\\cursor\\resources\\app\\bin',
'C:\\Users\\Rohan\\AppData\\Local\\com.Langflow\\uv',
'C:\\Users\\Rohan\\.local\\bin',
'C:\\Users\\Rohan\\AppData\\Local\\Microsoft\\WindowsApps',
'C:\\Users\\Rohan\\AppData\\Roaming\\npm',
'C:\\Users\\Rohan\\AppData\\Local\\Programs\\Microsoft VS Code\\bin',
'C:\\Terraform',
'C:\\ProgramData\\miniconda3\\Library\\bin\\conda.bat',
'C:\\ProgramData\\miniconda3\\Scripts\\conda.exe',
'C:\\ProgramData\\miniconda3\\condabin\\conda.bat',
'C:\\ProgramData\\miniconda3',
'C:\\ProgramData\\miniconda3\\Library\\bin',
'C:\\ProgramData\\miniconda3\\Scripts',
'C:\\Users\\Rohan\\AppData\\Local\\Programs\\Ollama',
'C:\\Users\\Rohan\\AppData\\Local\\Programs\\cursor\\resources\\app\\bin',
[length]: 37
]
}
} %o
2025-07-21T12:05:43.812Z [PostgresMCPServer] [info] Server started and connected successfully { metadata: undefined }
2025-07-21T12:05:43.861Z [PostgresMCPServer] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0} { metadata: undefined }
Failed to run server
Traceback (most recent call last):
File "C:\Users\Rohan\AppData\Local\uv\cache\archive-v0\PQBi79xgW5oSnoZKAozUC\Lib\site-packages\mcp\cli\cli.py", line 343, in run
server = _import_server(file, server_object)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\Rohan\AppData\Local\uv\cache\archive-v0\PQBi79xgW5oSnoZKAozUC\Lib\site-packages\mcp\cli\cli.py", line 141, in _import_server
spec.loader.exec_module(module)
File "<frozen importlib._bootstrap_external>", line 999, in exec_module
File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
File "C:\Users\Rohan\Desktop\MCP_newProjects\postgress-mcp\server.py", line 5, in <module>
import asyncpg
ModuleNotFoundError: No module named 'asyncpg'
2025-07-21T12:05:48.536Z [PostgresMCPServer] [info] Server transport closed { metadata: undefined }
2025-07-21T12:05:48.537Z [PostgresMCPServer] [info] Client transport closed { metadata: undefined }
2025-07-21T12:05:48.538Z [PostgresMCPServer] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log. { metadata: undefined }
2025-07-21T12:05:48.539Z [PostgresMCPServer] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) { metadata: { context: 'connection', stack: undefined } }
2025-07-21T12:05:48.541Z [PostgresMCPServer] [info] Client transport closed { metadata: undefined }


In the error log, I can see issue with asyncpg import but its already installed and there no error on IDE as well, only when i try to add it as mcp tool. Here is pyproject.toml file -

[project]
name = "postgress-mcp"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = [
"asyncpg>=0.30.0",
"httpx>=0.28.1",
"mcp[cli]>=1.12.0",
]


Can someone please help in identifying the mistake.

I ran the code in server.py and expected that the mcp tool would work but instead its showing connection error everywhere.

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