What this does

MCP clients connect to remote servers over SSE (Server-Sent Events) or WebSocket transports, enabling LLMs to call tools hosted on different machines or services.

Steps

Run an MCP server with SSE transport. Expose tools over HTTP.

from mcp.server import Server
from mcp.server.sse import SseServerTransport
from starlette.applications import Starlette
from starlette.routing import Route

server = Server("remote-tools")

@server.tool("hello")
async def hello(name: str) -> str:
    return f"Hello, {name}!"

sse = SseServerTransport("/messages")

async def handle_sse(request):
    async with sse.connect_sse(request.scope, request.receive, request._send) as (read, write):
        await server.run(read, write)

app = Starlette(routes=[
    Route("/sse", endpoint=handle_sse),
    Route("/messages", endpoint=sse.handle_post_message, methods=["POST"]),
])

Run the server with Uvicorn.

pip install uvicorn
uvicorn app:app --host 0.0.0.0 --port 8000

Connect a client to the remote server. Use SseClient for SSE transport.

from mcp.client import sse_client
from mcp import Client

async def connect_remote():
    async with sse_client("http://localhost:8000/sse") as (read, write):
        client = Client(read, write)
        tools = await client.list_tools()
        for t in tools:
            print(f"Remote tool: {t.name}: {t.description}")

        result = await client.call_tool("hello", {"name": "Remote"})
        print(result.content[0].text)

Handle authentication. Pass tokens via headers or query parameters.

async def connect_with_auth():
    headers = {"Authorization": "Bearer sk-my-token"}
    async with sse_client(
        "http://localhost:8000/sse",
        headers=headers
    ) as (read, write):
        client = Client(read, write)
        tools = await client.list_tools()
        print(f"Authenticated. Found {len(tools)} tools.")

Reconnection on disconnection. Wrap the client in a retry loop.

import asyncio

async def persistent_client(url: str, max_retries=3):
    for attempt in range(max_retries):
        try:
            async with sse_client(url) as (read, write):
                client = Client(read, write)
                yield client
            break
        except Exception as e:
            if attempt == max_retries - 1:
                raise
            await asyncio.sleep(2 ** attempt)

Verification

curl -N http://localhost:8000/sse
# Expected: SSE stream with endpoint event

Common failures

CORS errors with browser clients. If the client runs in a browser, the server must include CORS headers. Use Starlette middleware.
SSE endpoint not found. The client URL must point to the exact SSE route (e.g., /sse). A trailing slash mismatch causes 404.
Connection timeout. Remote servers behind firewalls or NAT may drop idle SSE connections. Configure keepalive or use WebSocket transport instead.
Version mismatch - The installed package or runtime differs from the command shown; check the version first and rerun the smallest verification command.
Local environment drift - Another service, virtual environment, model, or path is being used; print the active binary path and configuration before changing the guide steps.

Related guides

How to Set Up MCP Server with Standard Tools
How to Create Custom MCP Tools for Your Application