MCP Proxy Wrapper

A lightweight, powerful wrapper for Model Context Protocol (MCP) servers that provides a comprehensive hook system for intercepting, monitoring, and modifying tool calls without changing your existing server code.

🚀 Features

• 🔧 Zero-Modification Wrapping: Wrap existing MCP servers without changing their code
• 🪝 Powerful Hook System: Execute custom logic before and after tool calls
• 🔌 Plugin Architecture: Extensible plugin system for reusable functionality
• 🔄 Argument & Result Modification: Transform inputs and outputs on-the-fly
• ⚡ Short-Circuit Capability: Skip tool execution with custom responses
• 🧠 Smart Plugins Included: LLM summarization and chat memory plugins
• 📊 Comprehensive Logging: Built-in monitoring and debugging support
• 🧪 Fully Tested: 100% test coverage with real MCP client-server validation
• 📘 TypeScript First: Complete TypeScript support with full type safety
• 🌐 Universal Compatibility: Works with any MCP SDK v1.6.0+ server

📦 Installation

npm install mcp-proxy-wrapper

🎯 Quick Start

Basic Usage

import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { wrapWithProxy } from 'mcp-proxy-wrapper';
import { z } from 'zod';

// Create your existing MCP server
const server = new McpServer({
  name: 'My Server',
  version: '1.0.0'
});

// Wrap it with proxy functionality
const proxiedServer = await wrapWithProxy(server, {
  hooks: {
    // Monitor all tool calls
    beforeToolCall: async (context) => {
      console.log(`🔧 Calling tool: ${context.toolName}`);
      console.log(`📝 Arguments:`, context.args);
    },
    
    // Process results
    afterToolCall: async (context, result) => {
      console.log(`✅ Tool completed: ${context.toolName}`);
      return result; // Pass through unchanged
    }
  },
  debug: true // Enable detailed logging
});

// Register tools normally
proxiedServer.tool('greet', { name: z.string() }, async (args) => {
  return {
    content: [{ type: 'text', text: `Hello, ${args.name}!` }]
  };
});

🔌 Plugin System

The MCP Proxy Wrapper includes a powerful plugin architecture that allows you to create reusable, composable functionality.

Using Built-in Plugins

import { LLMSummarizationPlugin, ChatMemoryPlugin } from 'mcp-proxy-wrapper';

const summarizationPlugin = new LLMSummarizationPlugin();
const memoryPlugin = new ChatMemoryPlugin();

const proxiedServer = await wrapWithProxy(server, {
  plugins: [
    summarizationPlugin,
    memoryPlugin
  ]
});

LLM Summarization Plugin

Automatically summarizes long tool responses using AI:

import { LLMSummarizationPlugin } from 'mcp-proxy-wrapper';

const plugin = new LLMSummarizationPlugin();
plugin.updateConfig({
  options: {
    provider: 'openai', // or 'mock' for testing
    openaiApiKey: process.env.OPENAI_API_KEY,
    model: 'gpt-4o-mini',
    minContentLength: 500,
    summarizeTools: ['research', 'analyze', 'fetch-data'],
    saveOriginal: true // Store original responses for retrieval
  }
});

const proxiedServer = await wrapWithProxy(server, {
  plugins: [plugin]
});

// Tool responses are automatically summarized
const result = await client.callTool({
  name: 'research',
  arguments: { topic: 'artificial intelligence' }
});

console.log(result._meta.summarized); // true
console.log(result._meta.originalLength); // 2000
console.log(result._meta.summaryLength); // 200
console.log(result.content[0].text); // "Summary: ..."

Chat Memory Plugin

Provides conversational interface for saved tool responses:

import { ChatMemoryPlugin } from 'mcp-proxy-wrapper';

const memoryPlugin = new ChatMemoryPlugin();
memoryPlugin.updateConfig({
  options: {
    provider: 'openai',
    openaiApiKey: process.env.OPENAI_API_KEY,
    saveResponses: true,
    enableChat: true,
    maxEntries: 1000
  }
});

const proxiedServer = await wrapWithProxy(server, {
  plugins: [memoryPlugin]
});

// Tool responses are automatically saved
await client.callTool({
  name: 'research',
  arguments: { topic: 'climate change', userId: 'user123' }
});

// Chat with your saved data
const sessionId = await memoryPlugin.startChatSession('user123');
const response = await memoryPlugin.chatWithMemory(
  sessionId,
  "What did I research about climate change?",
  'user123'
);
console.log(response); // AI response based on saved research

Creating Custom Plugins

import { BasePlugin, PluginContext, ToolCallResult } from 'mcp-proxy-wrapper';

class MyCustomPlugin extends BasePlugin {
  name = 'my-custom-plugin';
  version = '1.0.0';
  
  async afterToolCall(context: PluginContext, result: ToolCallResult): Promise<ToolCallResult> {
    // Add custom metadata
    return {
      ...result,
      result: {
        ...result.result,
        _meta: {
          ...result.result._meta,
          processedBy: this.name,
          customField: 'custom value'
        }
      }
    };
  }
}

const proxiedServer = await wrapWithProxy(server, {
  plugins: [new MyCustomPlugin()]
});

Plugin Configuration

const plugin = new LLMSummarizationPlugin();

// Runtime configuration updates
plugin.updateConfig({
  enabled: true,
  priority: 10,
  options: {
    minContentLength: 200,
    provider: 'openai'
  },
  includeTools: ['research', 'analyze'], // Only these tools
  excludeTools: ['chat'], // Skip these tools
  debug: true
});

Advanced Hook Examples

1. Argument Modification

const proxiedServer = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      // Add timestamp to all tool calls
      context.args.timestamp = new Date().toISOString();
      
      // Sanitize user input
      if (context.args.message) {
        context.args.message = context.args.message.trim();
      }
    }
  }
});

2. Result Enhancement

const proxiedServer = wrapWithProxy(server, {
  hooks: {
    afterToolCall: async (context, result) => {
      // Add metadata to all responses
      if (result.result.content) {
        result.result._meta = {
          toolName: context.toolName,
          processedAt: new Date().toISOString(),
          version: '1.0.0'
        };
      }
      return result;
    }
  }
});

3. Access Control & Short-Circuiting

const proxiedServer = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      // Block certain tools
      if (context.toolName === 'delete' && !context.args.adminKey) {
        return {
          result: {
            content: [{ type: 'text', text: 'Access denied: Admin key required' }],
            isError: true
          }
        };
      }
      
      // Rate limiting
      if (await isRateLimited(context.args.userId)) {
        return {
          result: {
            content: [{ type: 'text', text: 'Rate limit exceeded. Try again later.' }],
            isError: true
          }
        };
      }
    }
  }
});

4. Error Handling & Monitoring

const proxiedServer = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      // Log to monitoring service
      await analytics.track('tool_call_started', {
        tool: context.toolName,
        userId: context.args.userId,
        timestamp: Date.now()
      });
    },
    
    afterToolCall: async (context, result) => {
      // Handle errors
      if (result.result.isError) {
        await errorLogger.log({
          tool: context.toolName,
          error: result.result.content[0].text,
          context: context.args
        });
      }
      
      return result;
    }
  }
});

📚 Core Concepts

Hook System

The proxy wrapper provides two main hooks:

• beforeToolCall: Executed before the original tool function

  • Can modify arguments
  • Can short-circuit execution by returning a result
  • Perfect for validation, authentication, logging

• afterToolCall: Executed after the original tool function

  • Can modify the result
  • Must return a ToolCallResult
  • Ideal for post-processing, caching, analytics

Context Object

Every hook receives a ToolCallContext with:

interface ToolCallContext {
  toolName: string;              // Name of the tool being called
  args: Record<string, any>;     // Tool arguments (mutable)
  metadata?: Record<string, any>; // Additional context data
}

Result Object

The afterToolCall hook works with ToolCallResult:

interface ToolCallResult {
  result: any;                   // The tool's return value
  metadata?: Record<string, any>; // Additional result metadata
}

🔧 API Reference

wrapWithProxy(server, options)

Wraps an MCP server instance with proxy functionality.

Parameters:

• server (McpServer): The MCP server to wrap
• options (ProxyWrapperOptions): Configuration options

Returns: Promise<McpServer> - A new MCP server instance with proxy capabilities

ProxyWrapperOptions

interface ProxyWrapperOptions {
  hooks?: ProxyHooks;              // Hook functions
  plugins?: ProxyPlugin[];         // Plugin instances
  pluginConfig?: Record<string, any>; // Global plugin configuration
  metadata?: Record<string, any>;  // Global metadata
  debug?: boolean;                 // Enable debug logging
}

ProxyHooks

interface ProxyHooks {
  beforeToolCall?: (context: ToolCallContext) => Promise<void | ToolCallResult>;
  afterToolCall?: (context: ToolCallContext, result: ToolCallResult) => Promise<ToolCallResult>;
}

🧪 Testing

The MCP Proxy Wrapper includes comprehensive testing with real MCP client-server communication:

# Run all tests
npm test

# Run with coverage
npm run test:coverage

# Run specific test suites
npm test -- --testNamePattern="Comprehensive Tests"
npm test -- --testNamePattern="Edge Cases"
npm test -- --testNamePattern="Protocol Compliance"

Test Coverage

• ✅ 65+ comprehensive tests covering all functionality
• ✅ Real MCP client-server communication using InMemoryTransport
• ✅ Plugin system validation with integration tests
• ✅ Edge cases including concurrency, large data, Unicode handling
• ✅ Protocol compliance validation
• ✅ Error scenarios and stress testing
• ✅ Both TypeScript and JavaScript compatibility

🔄 Migration & Compatibility

MCP SDK Compatibility

• Supported: MCP SDK v1.6.0 and higher
• Tested: Fully validated with MCP SDK v1.12.1
• Note: Requires Zod schemas for proper argument passing

Upgrading Your Server

The proxy wrapper is designed to be a drop-in replacement:

// Before
const server = new McpServer(config);
server.tool('myTool', schema, handler);

// After  
const server = new McpServer(config);
const proxiedServer = await wrapWithProxy(server, { 
  hooks: myHooks,
  plugins: [new LLMSummarizationPlugin()]
});
proxiedServer.tool('myTool', schema, handler); // Same API!

🛠 Use Cases

1. Authentication & Authorization

const authProxy = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      if (!await validateApiKey(context.args.apiKey)) {
        return { result: { content: [{ type: 'text', text: 'Invalid API key' }], isError: true }};
      }
    }
  }
});

2. Rate Limiting

const rateLimitedProxy = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      const userId = context.args.userId;
      if (await rateLimiter.isExceeded(userId)) {
        return { result: { content: [{ type: 'text', text: 'Rate limit exceeded' }], isError: true }};
      }
      await rateLimiter.increment(userId);
    }
  }
});

3. Caching

const cachedProxy = wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      const cacheKey = `${context.toolName}:${JSON.stringify(context.args)}`;
      const cached = await cache.get(cacheKey);
      if (cached) {
        return { result: cached };
      }
    },
    afterToolCall: async (context, result) => {
      const cacheKey = `${context.toolName}:${JSON.stringify(context.args)}`;
      await cache.set(cacheKey, result.result, { ttl: 300 });
      return result;
    }
  }
});

4. Analytics & Monitoring

const monitoredProxy = await wrapWithProxy(server, {
  hooks: {
    beforeToolCall: async (context) => {
      await metrics.increment('tool_calls_total', { tool: context.toolName });
      context.startTime = Date.now();
    },
    afterToolCall: async (context, result) => {
      const duration = Date.now() - context.startTime;
      await metrics.histogram('tool_call_duration', duration, { tool: context.toolName });
      return result;
    }
  }
});

5. AI-Powered Enhancement

import { LLMSummarizationPlugin, ChatMemoryPlugin } from 'mcp-proxy-wrapper';

const aiEnhancedProxy = await wrapWithProxy(server, {
  plugins: [
    new LLMSummarizationPlugin({
      options: {
        provider: 'openai',
        openaiApiKey: process.env.OPENAI_API_KEY,
        summarizeTools: ['research', 'analyze', 'fetch-data'],
        minContentLength: 500
      }
    }),
    new ChatMemoryPlugin({
      options: {
        provider: 'openai',
        openaiApiKey: process.env.OPENAI_API_KEY,
        saveResponses: true,
        enableChat: true
      }
    })
  ]
});

// Long research responses are automatically summarized
// All responses are saved for conversational querying

🤝 Contributing

We welcome contributions! Please see our Contributing Guide for details.

Development Setup

git clone https://github.com/crazyrabbitLTC/mcp-proxy-wrapper.git
cd mcp-proxy-wrapper
npm install
npm run build
npm test

📄 License

MIT License - see LICENSE file for details.

🔗 Links

• Model Context Protocol
• MCP TypeScript SDK
• GitHub Repository
• Issues & Support

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Created by Dennison Bertram