MCP Transport Methods: stdio vs Streamable HTTP (Not WebSocket)
The MCP spec defines two real transports — stdio and Streamable HTTP (which replaced the older separate HTTP+SSE combination). WebSocket isn't a standard MCP transport, despite showing up in some comparisons.
Worth correcting up front: the MCP specification defines two transports — stdio and Streamable HTTP. WebSocket is not a standard MCP transport, despite occasionally appearing in comparison articles; if you see it listed as a first-class MCP transport option, that's inaccurate against the actual spec.
stdio: The Local Development Default
Standard input/output is how a client launches an MCP server as a local child process and exchanges JSON-RPC messages over its stdin/stdout streams. It's the default for desktop clients like Claude Desktop connecting to locally-installed servers — fast, requires no network configuration, and easy to debug since you can watch the raw JSON-RPC lines directly in a terminal.
Streamable HTTP: The Remote Server Standard
Streamable HTTP is the current spec's answer for remote servers — it replaced an earlier, separate combination of plain HTTP POST requests plus a distinct Server-Sent Events (SSE) endpoint for server-to-client streaming. Streamable HTTP unifies this into a single endpoint that can respond with either a direct JSON response or an SSE stream depending on what the interaction needs, simplifying what used to require managing two separate connection types.
Why SSE Still Comes Up
Because Streamable HTTP is a relatively recent spec addition, plenty of currently-deployed clients and servers still speak the older HTTP+SSE combination rather than the newer unified transport. Before building against either, check what your specific target client actually supports — the spec has moved forward, but real-world adoption of the newest version takes time to propagate.
Choosing Between Them in Practice
- stdio — single local user, desktop client, fastest to debug, zero network exposure.
- Streamable HTTP (or the older HTTP+SSE combo) — multiple remote clients, hosted/production deployment, requires real authentication (this is exactly why OAuth 2.1 matters so much for servers like Swiggy's and Zomato's, which are inherently remote and multi-user).
Real production servers covered on this site confirm this split cleanly: Zerodha's Kite MCP supports stdio, HTTP, SSE, and a hybrid production mode, explicitly recommending HTTP over stdio for better performance and reliability once you're past local single-user development.