Streamable HTTP & SSE — Transport Layers

Remote Connections: Streamable HTTP

To host an MCP Server in the cloud (e.g., on Vercel, Cloudflare Workers, or AWS) so multiple clients can connect over standard web infrastructure, the official network standard is Streamable HTTP (introduced in 2025-03-26 to replace the deprecated 2024-11-05 dual-endpoint HTTP+SSE transport, and refined into a fully Stateless Core in 2026-07-28).

How Streamable HTTP Works

1. The Server exposes a single unified HTTP endpoint (e.g., /mcp) rather than separate /sse and /messages endpoints.
2. The Client sends JSON-RPC requests via standard HTTP POST with Accept: application/json, text/event-stream.
3. The Server responds directly with application/json for immediate results or upgrades that response to text/event-stream (SSE) to stream intermediate progress notifications before returning the final result.

// TypeScript SDK v2 (@modelcontextprotocol/server) — Stateless Web-Standard Handler:
import { createMcpHandler, McpServer } from "@modelcontextprotocol/server";

const handler = createMcpHandler(() => new McpServer({ name: "cloud-mcp", version: "1.0.0" }));
export default { fetch: handler.fetch }; // Single /mcp endpoint

// TypeScript SDK v1 (@modelcontextprotocol/sdk) — Stateless Streamable HTTP on Express:
import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
app.post("/mcp", async (req, res) => {
  const transport = new StreamableHTTPServerTransport({ sessionIdGenerator: undefined });
  await server.connect(transport);
  await transport.handleRequest(req, res, req.body);
});
// Deprecated 2024-11-05 dual-endpoint transport (DO NOT use for new servers):
// import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";