ClosedMCP
Browse guides · Serverless MCPs

The ClosedMCP library

What you use depends on where your MCP server runs.

Your MCP runs...Use
On ClosedMCP (a Serverless MCP)the hosted contract below: four headers in, two _meta keys out. Nothing to install.
On your own serversthe Log in with ClosedMCP SDK (@closedmcp/sdk for TypeScript, closedmcp for Python, also Go and Rust). See SDK reference.

Do not wrap a hosted app with the SDK's server wrapper (serveWithClosedMcp / serve_with_closedmcp). It expects a signed pass in Authorization: Bearer, and ClosedMCP removes that header before a call reaches a hosted app, so every call would be rejected.

A small hosted helper module for the TypeScript and Python SDKs is coming.

What is already installed

Every hosted app and every closedmcp_run sandbox starts from the same base image:

  • Node 22 with @modelcontextprotocol/sdk, fastmcp, @closedmcp/sdk, pg and postgres, found through NODE_PATH (so load them with require).
  • Python 3.12 with mcp, fastmcp 2, psycopg[binary], SQLAlchemy, uvicorn and closedmcp.
  • psql, bash, git, curl and jq.

Your own node_modules or Python packages win over these.

In: who is calling

HeaderMeaning
X-ClosedMCP-Userthe person's ID, stable
X-ClosedMCP-Emailtheir email
X-ClosedMCP-Orgtheir company's org ID
X-ClosedMCP-Clientthe AI app they use; display only

ClosedMCP sets these on every call and removes copies sent by anyone else.

  • Python (FastMCP 2): get_http_headers(include_all=True).get("x-closedmcp-email"), with from fastmcp.server.dependencies import get_http_headers.
  • Node (official MCP SDK): extra.requestInfo?.headers["x-closedmcp-email"] in the tool handler.

Out: event channels

_meta key in a tool resultEffect
"closedmcp/channel": {name, topic, ttl}opens a channel the caller can wait on
"closedmcp/events": [{topic, data}, ...]delivers each data to every open channel of this app with that topic
  • Python (FastMCP 2): return ToolResult(content="...", meta={...}), with from fastmcp.tools.tool import ToolResult.
  • Node (official MCP SDK): return { content: [...], _meta: {...} }.

Details and limits: Event channels.

For AI agents: this page as markdown is at /docs/library.md, and the closedmcp_guide tool returns it with topic library.