What is the Streamable HTTP transport?
The MCP transport for remote servers: one HTTPS endpoint (such as https://example.com/mcp) that receives JSON-RPC messages as POST requests and may stream replies as server-sent events.
It replaced the older HTTP+SSE transport from protocol version 2024-11-05. The client sends every message as a new POST with an Accept header listing both application/json and text/event-stream; the server answers with a single JSON object or opens an SSE stream.
A server may assign an Mcp-Session-Id header at initialization, which the client then repeats on every request, and clients send MCP-Protocol-Version on requests after the handshake. Servers must validate the Origin header to block DNS rebinding.
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Related terms
- stdio transportThe MCP transport for local servers: the client starts the server as a subprocess and they exchange newline-delimited JSON-RPC messages over standard input and output.
- MCP serverA program that exposes tools, resources or prompts to AI applications over the Model Context Protocol.
- JSON-RPC 2.0The small remote-procedure-call format MCP uses: requests with jsonrpc, id, method and params; responses with the same id and either result or error.