MCP MQTT Server

An MCP (Model Context Protocol) server that provides MQTT operations to LLM agent pipelines through a discoverable interface. The server supports fine-grained topic permissions with wildcard matching and provides comprehensive MQTT functionality for MCP clients.

Features

• MCP Server Interface: MCP server implementation for MQTT operations
• Topic Permissions: Fine-grained read/write permissions with MQTT wildcard support (+ and #)
• Authentication: MQTT broker authentication support
• Discoverable: MCP resources for topic discovery and examples
• Configurable: JSON-based configuration with schema validation
• Async Support: Full async/await support for non-blocking operations

Architecture

┌─────────────────┐    ┌──────────────────────────────────┐
│   MCP Client    │    │         mcpMQTT Application      │
│                 │    │                                  │
│  ┌───────────┐  │    │  ┌─────────────┐                 │
│  │   Agent   │  │◄──►│  │ MCP Server  │                 │
│  └───────────┘  │    │  └─────────────┘                 │
└─────────────────┘    │         │                        │
                       │  ┌─────────────────────────────┐ │
┌─────────────────┐    │  │   Topic Permission Manager  │ │
│  MQTT Broker    │◄──►│  └─────────────────────────────┘ │
└─────────────────┘    │         │                        │
                       │  ┌─────────────┐                 │
                       │  │ MQTT Client │                 │
                       │  │  Manager    │                 │
                       │  └─────────────┘                 │
                       └──────────────────────────────────┘

Installation

pip install mcpMQTT

Configuration

Configuration File Structure

Create a configuration file at ~/.config/mcpmqtt/config.json or specify a custom path when launching the utility on the command line using the --config parameter:

{
  "mqtt": {
    "host": "localhost",
    "port": 1883,
    "username": null,
    "password": null,
    "keepalive": 60
  },
  "topics": [
    {
      "pattern": "sensors/+/temperature",
      "permissions": ["read"],
      "description": "Temperature sensor data from any location (+ matches single level like 'room1', 'room2'. Known rooms are 'exampleroom1' and 'exampleroom2'). Use subscribe, not read on this topic. Never publish."
    },
    {
      "pattern": "sensors/+/humidity",
      "permissions": ["read"],
      "description": "Humidity sensor data from any location. (+ matches single level like 'room1', 'room2'. Known rooms are 'exampleroom1' and 'exampleroom2'). Use subscribe, not read on this topic. Never publish. Data returned as %RH"
    },
    {
      "pattern": "actuators/#",
      "permissions": ["write"],
      "description": "All actuator control topics (# matches multiple levels like 'lights/room1'. To enable a light you write any payload to 'lights/room1/on', to disable you write to 'lights/room1/off')"
    },
    {
      "pattern": "status/system",
      "permissions": ["read"],
      "description": "System status information - exact topic match"
    },
    {
      "pattern": "commands/+/request",
      "permissions": ["write"],
      "description": "Command request topics for request/response patterns"
    },
    {
      "pattern": "commands/+/response",
      "permissions": ["read"],
      "description": "Command response topics for request/response patterns"
    }
  ],
  "logging": {
    "level": "INFO",
    "logfile": null
  }
}

Configuration Sections

• mqtt: MQTT broker connection settings
• topics: Topic patterns with permissions and descriptions
• logging: Application logging level

Topic Patterns and Permissions

Wildcard Support:

• +: Single-level wildcard (matches one topic level)
• #: Multi-level wildcard (matches multiple levels, must be last)

Permissions:

• read: Can subscribe to topics and receive messages
• write: Can publish messages to topics
• Both permissions can be combined: ["read", "write"]

Examples:

• sensors/+/temperature matches sensors/room1/temperature, sensors/kitchen/temperature
• actuators/# matches actuators/lights, actuators/lights/room1/brightness
• status/system matches exactly status/system

Usage

Running the MCP Server

Using the installed script:

mcpMQTT

Or using the module directly:

python -m mcpMQTT.app.mcp_server

With custom configuration:

mcpMQTT --config /path/to/config.json --log-level DEBUG
# or
python -m mcpMQTT.app.mcp_server --config /path/to/config.json --log-level DEBUG

MCP Tools

The MCP server provides three tools for MQTT operations:

mqtt_publish

Publish messages to MQTT topics.

{
  "topic": "sensors/room1/temperature",
  "payload": "22.5",
  "qos": 0
}

mqtt_subscribe

Subscribe to topics and collect messages.

{
  "topic": "sensors/+/temperature",
  "timeout": 30,
  "max_messages": 5
}

mqtt_read

Subscribe to a topic and wait for a single message.

{
  "topic" : "sensors/+/temperature",
  "timeout" : 5
}

mqtt_query

Request/response pattern for MQTT communication.

{
  "request_topic": "commands/room1/request",
  "response_topic": "commands/room1/response",
  "payload": "get_status",
  "timeout": 5
}

MCP Resources

mcpmqtt://topics/allowed

Get allowed topic patterns with permissions and descriptions.

mcpmqtt://topics/examples

Get examples of how to use topic patterns with wildcards.

Development

Project Structure

mcpMQTT/
├── app/
│   ├── __init__.py
│   ├── mcp_server.py        # MCP server implementation and entry point
│   └── mqtt_client.py       # Enhanced MQTT client manager
├── config/
│   ├── config_manager.py    # Configuration loading and validation
│   ├── schema.py           # Pydantic models and validation
│   ├── example_config.json # Example configuration file
│   └── example_with_logging.json # Example with logging configuration
├── examples/
│   ├── example_config.json        # Basic configuration example
│   └── example_with_logging.json  # Configuration with file logging
├── pyproject.toml
├── LOGGING_USAGE.md        # Detailed logging documentation
└── README.md

Configuration Examples

For detailed configuration examples, see the examples/ folder:

• example_config.json - Basic configuration with multiple topic patterns
• example_with_logging.json - Configuration with file logging enabled

Examples

MCP Client Integration

This MCP server uses the stdio protocol. This means that it should be launched by your LLM orchestrator.

A typical configuration (mcp.json) may look like the following:

{
  "mcpServers": {
    "mqtt": {
      "command": "mcpMQTT",
      "args": [
        "--config /usr/local/etc/mcpMQTT.conf"
      ],
      "env": {
        "PYTHONPATH": "/just/an/example/path/"
      },
      "timeout": 300,
      "alwaysAllow": [
        "mqtt_read"
      ]
    }
  }
}

Security Considerations

Keep in mind that this MCP allows an agent to subscribe to and publish to all topics that are exposed to the user associated with him on the MQTT broker. You have to perform fine grained configuration on your MQTT broker to limit which features the MCP can actually access or manipulate.

License

See LICENSE.md