MCP Server with Clerk & Express

A minimal example of an MCP server endpoint using Express and Clerk for authentication. At the moment, it only exposes a streamable http handler. It could be adapted to handle SSE as well if necessary though. The purpose of this example is to serve as a proof of concept!

Getting started

• Make sure you’re running Node.js >= 22.18 — the dev script runs TypeScript directly using Node’s type stripping.
• Run pnpm i to install dependencies.
• Create a Clerk application, then toggle on the Dynamic client registration option in the OAuth applications page in the Clerk Dashboard.
• Run cp .env.example .env and copy your Clerk API keys from the API keys page in the Clerk Dashboard into the .env file.
• Run pnpm run dev to start the server.
• You should be able to connect to it now from any client that supports the latest version of the MCP spec. A cursor configuration is provided as a test.

Connecting to the server

To test in cursor, for example, add the following config to your mcp config file:

"mcp-clerk-express": {
  "url": "http://localhost:3000/mcp"
}

HTTPS Setup (Optional)

By default, the server runs on HTTP only. To enable HTTPS for development (useful for testing with some clients), you’ll need to generate locally trusted certificates:

1. Install mkcert (if not already installed):

   # macOS
   brew install mkcert
   
   # Windows (using Chocolatey)
   choco install mkcert
   
   # Linux
   # See https://github.com/FiloSottile/mkcert#installation
   

2. Setup local certificate authority:

   mkcert -install
   

3. Generate certificates:

   mkcert localhost 127.0.0.1 ::1
   mkdir -p cert
   mv localhost+2*.pem cert/
   

4. Restart the server - certificate files aren’t watched, so stop and rerun pnpm run dev. On startup, the server detects the certificates and starts both HTTP (port 3000) and HTTPS (port 3001) servers.

The certificates are gitignored, so each developer needs to generate their own locally trusted certificates.