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Elysia MCP Plugin

A comprehensive ElysiaJS plugin for implementing Model Context Protocol (MCP) servers with HTTP transport support.

Features

• HTTP Transport: Full HTTP-based MCP transport with Streamable HTTP
• Session Management: Stateful session handling via headers
• Type-Safe: Built with TypeScript and Zod validation
• Easy Integration: Simple plugin architecture for Elysia apps
• Comprehensive Support: Tools, Resources, Prompts, and Logging
• Custom Logger Support: Use any logger (pino, winston, bunyan, etc.)
• Error Handling: Proper JSON-RPC 2.0 error responses
• Testing: Full unit test coverage with Bun test runner

Installation

bun add elysia-mcp
# or
npm install elysia-mcp

Starter Template

To quickly get started with a pre-configured Elysia MCP project, you can use our starter template:

# Create a new project from the starter template
bun create https://github.com/kerlos/elysia-mcp-starter my-mcp-project

# Navigate to the project
cd my-mcp-project

# Install dependencies
bun install

# Start development server
bun run dev

The elysia-mcp-starter template includes:

• Pre-configured Elysia setup with MCP plugin
• TypeScript configuration
• Development scripts
• Basic project structure
• Example MCP server implementation

Quick Start

import { Elysia } from 'elysia';
import { mcp } from 'elysia-mcp';
import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { z } from 'zod';

const app = new Elysia()
  .use(
    mcp({
      serverInfo: {
        name: 'my-mcp-server',
        version: '1.0.0',
      },
      capabilities: {
        tools: {},
        resources: {},
        prompts: {},
        logging: {},
      },
      setupServer: async (server: McpServer) => {
        // Register your MCP tools, resources, and prompts here
        server.registerTool(
          'echo',
          {
            description: 'Echoes back the provided text',
            inputSchema: {
              text: z.string().describe('Text to echo back'),
            },
          },
          async (args) => {
            return {
              content: [{ type: 'text', text: `Echo: ${args.text}` }],
            };
          }
        );
      },
    })
  )
  .listen(3000);

Usage

Running the Examples

Basic Example:

# Run the basic example server (port 3000)
bun run example

# Or with development mode (auto-restart)
bun run dev

Multiple Servers Example:

# Run the multiple MCP servers example (port 3000)
bun example:multi

This example demonstrates how to create multiple MCP plugins in a single Elysia application:

• Math Operations Plugin (/math) - Basic arithmetic tools:

  • add - Add two numbers
  • multiply - Multiply two numbers
  • power - Calculate base to the power of exponent

• Text Utilities Plugin (/text) - Text processing tools:

  • uppercase - Convert text to uppercase
  • word_count - Count words in text
  • reverse - Reverse text characters
  • replace - Replace text with global matching

Testing with MCP Inspector

1. Install MCP Inspector:

   npx @modelcontextprotocol/inspector
   

2. Connect to your server:

   • Basic Example: http://localhost:3000/mcp
   • Multiple Servers Example:
     • Math Plugin: http://localhost:3000/math
     • Text Plugin: http://localhost:3000/text

Configuration Options

• serverInfo: Server information
• capabilities: MCP capabilities to advertise
• logger: Custom logger instance (pino, winston, etc.) - see Custom Logger section
• setupServer: Callback to register tools, resources, and prompts
• basePath: Base path for MCP endpoints (default: '/mcp')
• enableJsonResponse: Enable JSON response mode instead of SSE streaming
• stateless: Enable stateless mode (no session management)
• authentication: Authentication handler for protected routes
• eventStore: Event store for resumability support

Session Management

The plugin automatically handles session management via the Mcp-Session-Id header. Each session maintains its own state and can be terminated cleanly.

Modular Handler Architecture

The plugin supports a modular handler architecture that allows you to create specialized endpoints for different MCP capabilities:

import {
  mcp,
  ToolsHandler,
  ResourcesHandler,
  PromptsHandler,
} from 'elysia-mcp';

const app = new Elysia().use(
  mcp({
    /* config */
  })
);

Custom Logger

The plugin supports custom logger instances, allowing you to use any logging library that conforms to the ILogger interface:

interface ILogger {
  info(message: string, ...args: unknown[]): void;
  error(message: string, ...args: unknown[]): void;
  warn(message: string, ...args: unknown[]): void;
  debug(message: string, ...args: unknown[]): void;
}

Using Pino Logger

import { Elysia } from 'elysia';
import { mcp } from 'elysia-mcp';
import pino from 'pino';

const logger = pino({ level: 'debug' });

const app = new Elysia()
  .use(
    mcp({
      logger, // Pass your custom logger
      serverInfo: {
        name: 'my-mcp-server',
        version: '1.0.0',
      },
      // ... other options
    })
  )
  .listen(3000);

Using Winston Logger

import winston from 'winston';

const logger = winston.createLogger({
  level: 'debug',
  format: winston.format.json(),
  transports: [new winston.transports.Console()],
});

const app = new Elysia()
  .use(
    mcp({
      logger, // Pass your winston logger
      // ... other options
    })
  )
  .listen(3000);

Default Console Logger

If you don't provide a custom logger, the plugin will use a default console logger when enableLogging is set to true:…