Getting MCP server to host through HTTP

[mayonesa]

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Your Question

I wrote a successful MCP server that serves through stdio transport. I would also like to serve through the "sse" transport. I am using Python SDK.
On the server side, I simply changed stdio to sse in FastMCP().run(). Here's the code for server.py:

from mcp.server import FastMCP

# Initialize FastMCP server
mcp = FastMCP("weather", host="localhost", port=8080)


@mcp.tool()
async def get_forecast(city: str, state: str) -> str:
    """Get weather forecast for a city in a state.

    Args:
        city: City name
        state: Two-letter US state code (e.g. CA, NY)
    """
    # TODO: replace w/ actual forecast
    return """
Now:
Temperature: 42° F
Wind: 10 mph N
Forecast: Mostly sunny, with a high near 42. North wind around 10 mph.
"""


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

I attempt to run it as:

% mcp run server.py

but it don't get the terminal prompt back. Any calls to http://localhost:8080 time out.

When I attempt to connect through MCP Inspector,

% mcp dev server.py

, I get time out:

Starting MCP inspector...
New SSE connection
Query parameters: { transportType: 'sse', url: 'http://localhost:8080/sse' }
SSE transport: url=http://localhost:8080/sse, headers=

🔍 MCP Inspector is up and running at http://localhost:5173 🚀
Error in /sse route: SseError: SSE error: TypeError: fetch failed: Connect Timeout Error
    at _eventSource.onerror (file:///home/juancho/.npm/_npx/5a9d879542beca3a/node_modules/@modelcontextprotocol/sdk/dist/esm/client/sse.js:29:31)
    at EventSource.scheduleReconnect_fn (file:///home/juancho/.npm/_npx/5a9d879542beca3a/node_modules/@modelcontextprotocol/sdk/node_modules/eventsource/dist/index.js:248:53)
    at file:///home/juancho/.npm/_npx/5a9d879542beca3a/node_modules/@modelcontextprotocol/sdk/node_modules/eventsource/dist/index.js:98:174
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5) {
  code: undefined,
  event: {
    type: 'error',
    message: 'TypeError: fetch failed: Connect Timeout Error',
    code: undefined,
    defaultPrevented: false,
    cancelable: false,
    timeStamp: 10850.674899000674
  }
}

Am I missing something?

[mayonesa]

run the server python instead:

% python server.py