Unable to connect to MCP sever

[dev4Kushal]

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Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

Hello everyone,

I’m working on a Python application that primarily handles backend functionality. Recently, I tried to implement an MCP server. The communication between my backend service layer and the MCP server is set up through a client using stdio.

However, when I try to call the API, the client is unable to reach the MCP server. I’ve tried several approaches, but since I’m new to MCP servers, I’m struggling to get this communication working.

Could anyone guide me on how to properly establish communication between the client and the MCP server with stdio?

[Tengen-12]

When using stdio for MCP communication, both the client and server must exchange newline-delimited JSON-RPC 2.0 messages over standard input/output (not HTTP).

Checklist:
Your MCP server should read from stdin, respond via stdout, and always flush() after printing.
Avoid logs on stdout use stderr instead.
Keep the server running; don’t exit after one request.
Each message must end with a newline (\n).
Test your server using the MCP Inspector if it works there, the issue is in how your client launches the subprocess.

for example
import sys, json
for line in sys.stdin:
req = json.loads(line)
res = {"jsonrpc": "2.0", "id": req.get("id"), "result": {"msg": "Hello MCP!"}}
print(json.dumps(res), flush=True)

ensure flushing, proper newline separation, and correct working directory when spawning the subprocess.