typescript-sdk/packages/middleware

Middleware packages

The packages in packages/middleware/* are thin integration layers that help you expose an MCP server in a specific runtime, platform, or web framework.

They intentionally do not add new MCP features or “business logic”. MCP functionality (tools, resources, prompts, transports, auth primitives, etc.) lives in @modelcontextprotocol/server (and other core packages). Middleware packages should primarily:

• adapt request/response types to the SDK (e.g. Node.js IncomingMessage/ServerResponse)
• provide small framework helpers (e.g. wiring, body parsing hooks)
• supply safe defaults for common deployment pitfalls (e.g. localhost DNS rebinding protection)

Packages

• @modelcontextprotocol/express — Express helpers (app defaults + Host header validation for DNS rebinding protection).
• @modelcontextprotocol/fastify — Fastify helpers (app defaults + Host header validation).
• @modelcontextprotocol/hono — Hono helpers (app defaults + JSON body parsing hook + Host header validation).
• @modelcontextprotocol/node — Node.js Streamable HTTP transport wrapper for IncomingMessage/ServerResponse.

Typical usage

Most servers use:

• @modelcontextprotocol/server for the MCP server implementation
• one middleware package for framework/runtime integration (this folder)
• (optionally) additional platform/framework dependencies (Express, Hono, etc.)