How do I use Modular MCP Server?

1. Click on "Install Server". 2. Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state. 3. In the chat, type @ followed by the MCP server name and your instructions, e.g., "@Modular MCP Server read the contents of config.json" That's it! The server will respond to your query, and you can continue using it as needed. Here is a step-by-step guide with screenshots.

Modular MCP Server

A config-driven, modular MCP (Model Context Protocol) server with zero dependencies. Just edit a JSON config file to enable/disable tools and plugins!

Features

Config-Driven: Enable/disable tools by editing config.json
Zero Dependencies: Pure Node.js (18+), no npm packages needed
Plugin Architecture: Easy to add new plugins
Security: Built-in access controls and sandboxing per tool
Simple: ~500 lines of core code
Fast: Minimal overhead, direct tool execution

Quick Start

# 1. Create or edit config.json
cp config.example.json config.json

# 2. Start the server
node server.js

# Or specify a config file
node server.js my-config.json

How It Works

Config File Structure

The config.json file controls everything:

{
  "server": {
    "name": "my-mcp-server",
    "version": "1.0.0"
  },
  "plugins": [
    {
      "name": "utils",
      "type": "builtin",
      "module": "utils",
      "enabled": true,
      "tools": [
        {
          "name": "echo",
          "enabled": true
        },
        {
          "name": "calculate",
          "enabled": true
        }
      ]
    }
  ]
}

That's it! No code changes needed to add/remove tools.

Adding a Tool

Want to enable file operations? Just edit the config:

{
  "plugins": [
    {
      "name": "filesystem",
      "type": "builtin",
      "module": "filesystem",
      "enabled": true,
      "tools": [
        {
          "name": "read_file",
          "enabled": true,
          "allowedPaths": [".", "/tmp"]
        },
        {
          "name": "write_file",
          "enabled": true
        }
      ]
    }
  ]
}

Restart the server - done!

Disabling a Tool

Set "enabled": false:

{
  "name": "delete_file",
  "enabled": false  // ← Tool won't be available
}

Built-in Plugins

Filesystem Plugin

File and directory operations with path restrictions.

Tools:

read_file - Read file contents
write_file - Write to files
list_directory - List directory contents
file_info - Get file metadata
delete_file - Delete files

Config Options:

{
  "name": "read_file",
  "enabled": true,
  "allowedPaths": [".", "/tmp"],  // Restrict access
  "readonly": false                // Make filesystem readonly
}

Shell Plugin

Execute shell commands with whitelist/blacklist support.

Tools:

exec_command - Execute shell commands

Config Options:

{
  "name": "exec_command",
  "enabled": true,
  "allowedCommands": ["ls", "pwd", "cat"],  // Whitelist
  "blockedCommands": ["rm", "sudo"],         // Blacklist
  "maxBuffer": 1048576                       // 1MB output limit
}

HTTP Plugin

Make HTTP requests with domain restrictions.

Tools:

http_get - GET requests
http_post - POST requests

Config Options:

{
  "name": "http_get",
  "enabled": true,
  "allowedDomains": ["api.github.com", "example.com"]
}

Utils Plugin

Utility functions for common tasks.

Tools:

echo - Echo back input (testing)
calculate - Safe math evaluation
timestamp - Get current time
base64_encode - Base64 encoding
base64_decode - Base64 decoding

Creating Custom Plugins

1. Create Plugin File

// plugins/my-plugin.js
export default {
  // Optional initialization
  async init(config) {
    console.log('Plugin initialized:', config);
  },

  tools: {
    my_tool: {
      description: 'Description of what this tool does',
      inputSchema: {
        type: 'object',
        properties: {
          input: {
            type: 'string',
            description: 'Input parameter'
          }
        },
        required: ['input']
      },
      async execute(args, config) {
        // args = input parameters
        // config = tool-specific config from config.json

        return `Result: ${args.input}`;
      }
    }
  }
};

2. Add to Config

{
  "plugins": [
    {
      "name": "my-plugin",
      "type": "builtin",
      "module": "my-plugin",
      "enabled": true,
      "tools": [
        {
          "name": "my_tool",
          "enabled": true,
          "customOption": "value"
        }
      ]
    }
  ]
}

3. Restart Server

That's it! Your tool is now available.

External Plugins

Load plugins from outside the project:

{
  "plugins": [
    {
      "name": "external-plugin",
      "type": "external",
      "module": "/absolute/path/to/plugin.js",
      "enabled": true,
      "tools": [...]
    }
  ]
}

Security Features

Path Restrictions

{
  "name": "read_file",
  "allowedPaths": ["./data", "/tmp"]  // Only these paths accessible
}

Command Whitelisting

{
  "name": "exec_command",
  "allowedCommands": ["ls", "cat", "grep"]  // Only these commands
}

Domain Filtering

{
  "name": "http_get",
  "allowedDomains": ["trusted-api.com"]  // Only these domains
}

Read-Only Mode

{
  "name": "write_file",
  "readonly": true  // Prevent writes
}

Configuration Reference

Server Config

{
  "server": {
    "name": "server-name",     // MCP server name
    "version": "1.0.0"         // Server version
  }
}

Plugin Config

{
  "name": "plugin-name",       // Unique plugin identifier
  "type": "builtin",           // "builtin" or "external"
  "module": "plugin-file",     // Plugin file/path
  "enabled": true,             // Enable/disable entire plugin
  "required": false,           // Fail if plugin can't load
  "tools": [...]               // Array of tool configs
}

Tool Config

{
  "name": "tool-name",         // Tool identifier
  "enabled": true,             // Enable/disable this tool
  // ... custom options passed to tool's execute()
}

Examples

Example 1: Read-Only Filesystem

{
  "plugins": [
    {
      "name": "filesystem",
      "type": "builtin",
      "module": "filesystem",
      "enabled": true,
      "tools": [
        {
          "name": "read_file",
          "enabled": true,
          "allowedPaths": ["/var/log"]
        },
        {
          "name": "list_directory",
          "enabled": true
        }
      ]
    }
  ]
}

Example 2: Safe Shell Access

{
  "plugins": [
    {
      "name": "shell",
      "type": "builtin",
      "module": "shell",
      "enabled": true,
      "tools": [
        {
          "name": "exec_command",
          "enabled": true,
          "allowedCommands": ["ls", "pwd", "cat", "grep", "find"],
          "blockedCommands": ["rm", "sudo", "su"],
          "maxBuffer": 1048576
        }
      ]
    }
  ]
}

Example 3: HTTP API Client

{
  "plugins": [
    {
      "name": "http",
      "type": "builtin",
      "module": "http",
      "enabled": true,
      "tools": [
        {
          "name": "http_get",
          "enabled": true,
          "allowedDomains": [
            "api.github.com",
            "httpbin.org"
          ]
        }
      ]
    }
  ]
}

Testing

Using MCP Inspector

# Install MCP Inspector
npm install -g @modelcontextprotocol/inspector

# Test your server
mcp-inspector node server.js

Manual Testing

Send JSON-RPC requests via stdin:

# Initialize
echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}' | node server.js

# List tools
echo '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' | node server.js

# Call a tool
echo '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"echo","arguments":{"message":"Hello!"}}}' | node server.js

Logging

Control log level via environment variable:

# Debug mode
LOG_LEVEL=DEBUG node server.js

# Quiet mode
LOG_LEVEL=ERROR node server.js

Log levels: ERROR, WARN, INFO (default), DEBUG

Architecture

┌─────────────────────────────────────┐
│         MCP Client (Claude)         │
└─────────────┬───────────────────────┘
              │ JSON-RPC over stdio
┌─────────────▼───────────────────────┐
│      core/mcp-protocol.js           │
│  (JSON-RPC handler, stdio I/O)      │
└─────────────┬───────────────────────┘
              │
┌─────────────▼───────────────────────┐
│    core/plugin-manager.js           │
│  (Loads plugins from config.json)   │
└─────────────┬───────────────────────┘
              │
      ┌───────┴───────┬─────────────┐
      │               │             │
┌─────▼─────┐  ┌──────▼──────┐  ┌──▼────┐
│filesystem │  │    shell    │  │  http │
│  plugin   │  │   plugin    │  │ plugin│
└───────────┘  └─────────────┘  └───────┘

Files

.
├── server.js                # Entry point
├── config.json              # Your configuration
├── config.example.json      # Example config
├── package.json             # Project metadata
├── core/
│   ├── mcp-protocol.js      # MCP/JSON-RPC implementation
│   ├── plugin-manager.js    # Plugin loader
│   └── logger.js            # Logging utility
├── plugins/
│   ├── filesystem.js        # File operations
│   ├── shell.js             # Shell commands
│   ├── http.js              # HTTP requests
│   └── utils.js             # Utilities
└── README.md                # This file

FAQ

Q: How do I add a new tool?

A: Edit config.json and add the tool to a plugin's tools array. Restart the server.

Q: Can I create my own plugins?

A: Yes! Create a .js file in plugins/ following the plugin structure, then reference it in config.json.

Q: How do I restrict file access?

A: Use the allowedPaths option in the filesystem tool config.

Q: Is this secure?

A: It has built-in security features (path restrictions, command whitelisting, etc.), but treat it like any tool that executes code - configure it carefully and run with appropriate permissions.

Q: Can I use this in production?

A: Yes, but review the security settings carefully. Consider running in a container or with restricted user permissions.

License

MIT

Contributing

Contributions welcome! The codebase is intentionally simple and zero-dependency to keep it maintainable.

Modular MCP Server

Features

Quick Start

How It Works

Config File Structure

Adding a Tool

Disabling a Tool

Built-in Plugins

Filesystem Plugin

Shell Plugin

HTTP Plugin

Utils Plugin

Creating Custom Plugins

1. Create Plugin File

2. Add to Config

3. Restart Server

External Plugins

Security Features

Path Restrictions

Command Whitelisting

Domain Filtering

Read-Only Mode

Configuration Reference

Server Config

Plugin Config

Tool Config

Examples

Example 1: Read-Only Filesystem

Example 2: Safe Shell Access

Example 3: HTTP API Client

Testing

Using MCP Inspector

Manual Testing

Logging

Architecture

Files

FAQ

Q: How do I add a new tool?

Q: Can I create my own plugins?

Q: How do I restrict file access?

Q: Is this secure?

Q: Can I use this in production?

License

Contributing

Resources

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Tools

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