Reject non-MCP transports
What you'll learn
MCP only has two transports: stdio and Streamable HTTP. WebSockets and gRPC are common in other systems but not MCP.
- MCP transports: stdio, Streamable HTTP. Closed list.
- WebSockets, gRPC, named pipes, raw TCP, message queues are *not* MCP.
- Streamable HTTP already streams (via SSE) — 'streaming' is not a reason to reach outside the spec.
The MCP spec lists exactly two transports: **stdio** and **Streamable HTTP**. Anything else — WebSockets, gRPC, named pipes, raw TCP, message queues — is *not* an MCP transport. The exam tests this directly and frequently uses 'WebSockets for streaming' or 'gRPC for typed schemas' as plausible-sounding distractors. They're wrong on sight.
Why the closed list matters: MCP's value is interoperability — any compliant client talks to any compliant server. A 'WebSocket MCP server' isn't compliant; clients can't speak it. The transports are deliberately small to keep the surface tractable. Streamable HTTP already supports streaming responses (it's literally Server-Sent Events under the hood), so 'I want streaming' is not a reason to reach for WebSockets.
The recognition skill: when a question lists four transport options and three are real protocols (WebSockets, gRPC, message queue) plus one MCP transport, the MCP transport is the only correct answer. Distractors lean on the candidate's familiarity with non-MCP protocols from other contexts. The shortcut: cross out anything that isn't stdio or Streamable HTTP (sometimes phrased as HTTP+SSE in older question banks).
Two transitional notes. The spec evolves; new transports may be added in future versions, but as of the current spec the two-transport rule holds. And 'Streamable HTTP' replaced the older name 'HTTP+SSE' — same protocol shape, both names may appear, both refer to the same transport.
Key points
- MCP transports: stdio, Streamable HTTP. Closed list.
- WebSockets, gRPC, named pipes, raw TCP, message queues are *not* MCP.
- Streamable HTTP already streams (via SSE) — 'streaming' is not a reason to reach outside the spec.
- Older name for Streamable HTTP: HTTP+SSE.
Examples
Options often include WebSockets (familiar from real-time apps), gRPC (familiar from microservices), and one MCP transport. Cross out the non-MCP options regardless of how plausible they sound.
Streamable HTTP supports streaming. Don't reach for WebSockets. The exam wants you to recognize the closed list, not relitigate it.
Pitfalls
- Picking WebSockets for 'real-time' framing. Streamable HTTP handles streaming.
- Picking gRPC for 'typed schemas' framing. MCP itself defines typed schemas at a higher layer.
- Assuming the spec must support some popular transport because it would be useful. The list is what it is.
Source notes: 00-academy-basics/notes/05-mcp-intro.md
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