Gen-AI Developer Classroom notes 11/Dec/2025

MCP Transport – SSE (Server Sent Events)

Normal HTTP

• Client Asks -> Server Replies -> Connection Closes
• If client wants updates, it must keep asking (polling)

SSE

• Client Asks once -> Server keeps replying many times
• Connection stays open
• Server Pushes updates like
  • Task started
  • 50 % progress
  • Here is the final output

Why MCP used to use SSE

• MCP needs to stream
  • logs
  • tool output
  • partial AI results
  • events
• Client listens on /sse
• MCP Server pushes events as they Happen
• No Polling, no delays.

• SSE is one way streaming: server -> client only

• SSE is a standard unidirectional communication from server to client over a single, long lived HTTP connection.

  • Protocol: SSE uses standard HTTP with MIME type text/event-stream
  • Client API: The browser uses EventSource API to recieve events
  • Format: Messages are sent as plain text with fields such as event, data and id each terminated by two endlines
• SSE is split into two parts
  • SSE endpoint: way to handshake connection b/w client and server
  • Messages endpoint: This is use to route messages to MCP servers and its features

Creating an SSE Server as a web app

• In python we need to use a framework supporting ASGI. For this we will be using Starlette.

• Starlette is a lightweight ASGI framework, We need uvicorn to run Starlette Application

• Create a new folder, initialize using uv and execute the following

uv add starlette uvicorn
.venv\Scripts\activate

• Add this code to main.py

from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route


async def homepage(request):
    return JSONResponse({"hello": "world"})

async def otherpage(request):
    return JSONResponse({"other": "page"})


app = Starlette(debug=True, routes=[
    Route("/", homepage),
    Route("/other", otherpage),
    ])

• run the application using uv run main:app

• Now access http://localhost:8000/ and http://localhost:8000/other
  

• Refer Here for the code written

Starlette and MCP

• Lets create a new folder and initialize and add the necessary dependencies uv add mcp[cli] httpx uvicorn starlette
• Create mcp server as usual
• Refer Here as a sample .