Protocol
SSE/HTTP
Understand MCP Streamable HTTP, SSE response streams, POST requests, GET streams, and hosted MCP endpoint behavior.
Definition
SSE/HTTP describes MCP communication over HTTP where clients send JSON-RPC messages with POST and servers may return JSON or open a server-sent events stream. The current MCP transport is commonly described as Streamable HTTP.
How Astrail Uses It
Astrail hosted MCP endpoints accept HTTP JSON-RPC requests and are designed for agents that connect to remote MCP servers. The runtime can return structured JSON responses and enforce HTTP-layer security controls.
Implementation Checklist
Accept JSON-RPC requests through POST at the MCP endpoint.
Set and validate content types and Accept headers consistently.
Use explicit authorization and origin checks for remote transports.
Plan for reconnects, timeouts, and resumability when using SSE streams.
FAQ
Is SSE required for every MCP HTTP response?
No. HTTP MCP responses can be ordinary JSON for a completed request, or an SSE stream when streaming server messages is needed.
Why do people still say SSE/HTTP?
Older and transitional implementations often used SSE terminology. The current specification describes Streamable HTTP with optional SSE streams.