MCP Server

Common errors

• Error: listen EADDRINUSE: address already in use :::4333

  cause The default port 4333, or a specified port, is already being used by another process on your system.
  fix Ensure no other applications are using port 4333. You can either stop the conflicting process or specify a different port when starting the `mcp-server` CLI (e.g., `npx mcp-server --port 8080`).

• Error [ERR_REQUIRE_ESM]: require() of ES Module ... Not supported by `require()` of a CommonJS module.

  cause You are attempting to import an ES Module (`import ... from '...'`) within a CommonJS context, or you are trying to `require()` this CJS-only package from an ESM context in a way that Node.js doesn't natively support.
  fix Ensure your project is configured as CommonJS if you are using `require()`, or use dynamic `import()` if you are in an ESM context and need to load a CJS module. For this specific package, stick to `const { createServer } = require('mcp-server');`.

• TypeError: createServer is not a function

  cause You might be trying to destructure `createServer` from a default export, or the module might not be correctly resolving the named export.
  fix Ensure you are using the correct CommonJS named import syntax: `const { createServer } = require('mcp-server');`. Do not use `const createServer = require('mcp-server');` as it will try to assign the entire `module.exports` object to `createServer`.

Warnings

• breaking This package is version 0.0.9 and was last published over five years ago. It is considered abandoned. Expect no further updates, bug fixes, or security patches. Using it in production is highly discouraged.
  Fix: For new projects or existing projects requiring a stable, secure, and modern MCP server, consider actively maintained alternatives like `mcp-framework` or `@modelcontextprotocol/server-everything`.
• gotcha The package explicitly enables CORS, which might be a security concern if not properly understood or restricted. An abandoned package with default CORS settings could introduce vulnerabilities.
  Fix: Review the source code if using this package to understand and tighten CORS policies if necessary. For any production environment, migrate to a supported MCP server solution.
• gotcha The documentation is minimal, and the API is purely CommonJS (CJS). Modern JavaScript projects primarily use ES Modules (ESM), which will require specific transpilation or bundler configurations if you attempt to integrate this CJS-only package into an ESM project.
  Fix: If programmatic use is required in an ESM project, you might need to use `createRequire` from the `module` module in Node.js, or configure your bundler (e.g., Webpack, Rollup) to handle CJS modules. However, migration to a modern MCP framework is strongly recommended.
• gotcha The `mcp-server` package implements a basic JSON-RPC 2.0 server with echo functionality. The Model-Client-Protocol (MCP) has advanced significantly, and this package likely lacks many features present in contemporary MCP implementations (e.g., richer tool definitions, diverse transports beyond basic HTTP, authentication mechanisms).
  Fix: Evaluate your specific MCP requirements. If you need advanced features, broader compatibility, or robust error handling, this package will be insufficient. Explore `mcp-framework`, `@modelcontextprotocol/sdk`, or other specialized MCP servers for more capable solutions.

Install

• npm install mcp-server npm
• yarn add mcp-server yarn
• pnpm add mcp-server pnpm

Imports

• createServer
  wrong:

  import { createServer } from 'mcp-server';

  correct:

  const { createServer } = require('mcp-server');

  This package is CommonJS-only. Programmatic usage requires `require()` syntax. Attempting to use ESM `import` will result in an error. The `createServer` function is the primary export for instantiating the server.
• createMethod
  wrong:

  import { createMethod } from 'mcp-server';

  correct:

  const { createMethod } = require('mcp-server');

  Like `createServer`, `createMethod` is a CommonJS export. It's used internally or for advanced customization of JSON-RPC methods.

Quickstart

Demonstrates how to run the `mcp-server` using its command-line interface via `npx`.

const { createServer } = require('mcp-server');

const server = createServer();

// Start the server on the default port (4333) or specified port
// The original package's `createServer` expects to be run directly
// or via its CLI; programmatic starting requires more context from
// the original source, but a typical usage would involve a listen call.
// The package's `index.js` sets up CLI arguments for the port.
// For programmatic use, one would typically extend or wrap its components.
// This example shows how to run it as a CLI tool as per the README:

console.log('To run the MCP server, use the CLI:');
console.log('  npx mcp-server');
console.log('This will start the server on port 4333 (default).');
console.log('\n// For programmatic control, further investigation into the 0.0.9 source is needed.');
console.log('// A simple programmatic start for a typical HTTP server might look like this (conceptual):');
console.log('// server.listen(4333, () => console.log(\'MCP server listening on port 4333\'));');
// A more direct interpretation of the original source is that `createServer` returns a function that sets up the HTTP server itself, rather than an Express-like app.
// Given its abandonment, directly using the CLI is the most documented path.