eMCP

A fork of the LiteMCP TS library with extended features like built-in authentication handling, and custom middleware.

Features

This is designed to be a near drop-in replacement for tools like LiteMCP. Because of this, all added features are currently optional.

• All current LiteMCP features
• Built-in authentication handler
• Custom layered middleware support

Quickstart

Install via Bun or NPM:

npm i emcp
# or use Bun (preferred)
bun add emcp

Basic Usage

(Optional) Run the examples:

bun run example:basic
bun run example:auth
bun run example:middleware
bun run example:advanced

const server = new eMCP("mcp-server-with-auth", "1.0.0", {
  authenticationHandler: async (request) => {
    // implement your custom auth logic here
    return true;
  },
});

// Request to this tool, or any other resource or prompt will
// require authentication governed by the handler
server.addTool({
  name: "add",
  description: "Add two numbers",
  parameters: z.object({
    a: z.number(),
    b: z.number(),
  }),
  execute: async (args) => {
    server.logger.debug("Adding two numbers", args);
    return args.a + args.b;
  },
});

Custom Middleware

const server = new eMCP("mcp-server-with-middleware", "1.0.0", {
  authenticationHandler: async (request) => {
    // implement your custom auth logic here
    return true;
  },
});

// This will time entire req -> res cycle, including middlewares
server.use(async (request, next) => {
  const startTime = Date.now();
  server.logger.debug("Request started", { method: request.method });

  // Wait for all inner middleware and the handler to complete
  const response = await next();

  const endTime = Date.now();
  server.logger.debug("Request completed", {
    method: request.method,
    duration: `${endTime - startTime}ms`,
  });

  return response;
});

How Middleware Works

Middleware in eMCP runs in order of registration. Once every middleware handler has hit it's next() block, then the standard MCP procedure will occur. Once the server is finished processing, then the order will run in reverse for middleware handlers with code after the next() block.

To put it simply, it looks something like this:

<---- Request received ----
1. Middleware 1
2. Middleware 2
<---- Pre-processing done ---->
4. Server handler
<---- Post-processing start ---->
5. Middleware 2
6. Middleware 1
---- Response sent ---->

If you're familiar with frameworks like Hono, then this will be familiar to you.

Roadmap

• Ergonomic MCP<->MCP communication
• Integration into frameworks

Why?

Because I felt like it