mcp-helmet

Production middleware for MCP servers. Auth, sessions, health checks, graceful shutdown, transport ergonomics. Composable middleware borrowed in spirit from Express's helmet.

mcp-helmet wraps the official @modelcontextprotocol/sdk with the things it doesn't ship: auto transport detection, content wrapping, health checks, graceful shutdown, session management, and auth middleware. One package. Composable. Drop what you don't need. Go from hello world to production in minutes, not days.

npm install mcp-helmet @modelcontextprotocol/sdk zod

Peer dependencies: @modelcontextprotocol/sdk ^1.29.0, zod ^3.22.0 or ^3.25 (v4). zod-to-json-schema is an optional peer for Zod v3 users.

Quickstart

The fastest way is the scaffolder:

npx mcp-helmet init my-server --transport http --auth bearer
cd my-server
npm install
npm run dev

You get a working MCP server with healthCheck(), gracefulShutdown(), optional auth, a multistage Dockerfile, and a typechecked tsconfig. Drop flags to skip pieces (--no-docker, --no-health, etc.) or customise after the fact.

Or wire it manually:

import { createServer } from "mcp-helmet";
import { z } from "zod";

const server = createServer({ name: "hello", version: "1.0.0" });

server.tool("greet", { name: z.string() }, async ({ name }) => {
  return `Hello, ${name}!`;
});

await server.start();

That's it. No transport wiring, no content array construction, no signal handlers. Run it:

# Local development (stdio, the default)
npx tsx src/index.ts

# Production (HTTP)
MCP_TRANSPORT=http PORT=3000 node dist/index.js

Same code, both modes.

Auth in 6 lines

Bearer token verification, with the verified principal available inside any tool handler:

import { createServer, bearerAuth, getAuthContext } from "mcp-helmet";

const server = createServer({ name: "secure", version: "1.0.0" });

server.use(bearerAuth({
  verify: async (token) => {
    const claims = await verifyJwt(token); // your call
    return { user: claims.sub, scopes: claims.scope?.split(" ") ?? [] };
  },
}));

server.tool("whoami", {}, async () => {
  const auth = getAuthContext();
  return { user: auth?.user, scopes: auth?.scopes };
});

await server.start();

The single-argument tool handler signature stays the same — getAuthContext() reads from AsyncLocalStorage, so it works from any depth in the async chain.

Why this exists

We audited 30 production MCP servers and 320 GitHub issues across the official SDKs. Three patterns kept showing up:

1. Every server rewrites the same 20-40 lines of setup. Transport selection, content wrapping, error formatting, signal handling. The SDK gives you the building blocks; this gives you the house.

2. Servers that work locally break in production. Docker containers exit after one response, Kubernetes pods lose sessions, no health check for load balancers to probe. 52% of remote MCP endpoints in a recent survey were dead.

3. Nobody can figure out auth. "How do I access the bearer token inside my tool?" is the most asked question across both SDK repos.

mcp-helmet solves these with composable middleware that extends the SDK without replacing it.

Status

v0.1.0-alpha — feature complete. Currently shipped:

• ✅ createServer() with auto content wrapping (string, object, Content[])

• ✅ Auto transport detection via MCP_TRANSPORT env var

• ✅ Zod v3 + v4 compatibility shim

• ✅ Composable middleware system (server.use(mw))

• ✅ healthCheck() middleware

• ✅ gracefulShutdown() middleware

• ✅ bearerAuth() and apiKeyAuth() middleware with AsyncLocalStorage-based getAuthContext()

• ✅ rateLimiter() middleware (sliding window, IP- or key-based, standard 429 headers)

• ✅ npx mcp-helmet init CLI scaffolder + Docker template

v0.1.0 stable will follow once the alpha cycle has 30+ days of real-world usage. v0.2 is on the ROADMAP: Redis-backed session store, structured logging middleware, Python port via FastMCP plugin.

How it relates to the official SDK

mcp-helmet is not a fork, an alternative, or a replacement. It's a convenience layer.

The SDK is a peer dependency. You bring your own version. If the SDK adds features that overlap, the toolkit middleware becomes a thin pass-through.

Requirements

• Node.js 20+

• @modelcontextprotocol/sdk ^1.29.0

• TypeScript 5.4+ (recommended, not required)

• Zod 3.22+ or 3.25+ (v4 via zod/v4 subpath)

Contributing

PRs and issues welcome. See CONTRIBUTING.md for setup, test, and PR conventions.

Security

See SECURITY.md for the responsible disclosure path.

License

MIT