Modbus MCP Server

An MCP server that standardizes and contextualizes Modbus data, enabling seamless integration of AI agents with industrial IoT systems.

Features

• Modbus Tools:
  • Read/write holding registers (read_register, write_register).
  • Read/write coils (read_coils, write_coil).
  • Read input registers (read_input_registers).
  • Read multiple holding registers (read_multiple_holding_registers).
• Prompt: Analyze Modbus register values with a customizable prompt (analyze_register).
• Flexible Connections: Supports Modbus over TCP, UDP, or serial, configured via environment variables.

Requirements

• Python: 3.10
• uv for dependency and virtual environment management.

Installation

1. Install uv:

   curl -LsSf https://astral.sh/uv/install.sh | sh

2. Clone the Repository:

   git clone https://github.com/kukapay/modbus-mcp.git
   cd modbus-mcp

3. Install Dependencies:

   uv sync

Configuration

The server connects to a Modbus device using parameters specified via environment variables. Set these variables in a .env file or your shell environment.

Environment Variables

Variable	Description	Default	Required
MODBUS_TYPE	Connection type: tcp, udp, or serial	tcp	Yes
MODBUS_HOST	Host address for TCP/UDP	127.0.0.1	For TCP/UDP
MODBUS_PORT	Port for TCP/UDP	502	For TCP/UDP
MODBUS_DEFAULT_SLAVE_ID	Slave ID	1	For TCP/UDP
MODBUS_SERIAL_PORT	Serial port (e.g., /dev/ttyUSB0, COM1)	/dev/ttyUSB0	For serial
MODBUS_BAUDRATE	Serial baud rate	9600	For serial
MODBUS_PARITY	Serial parity: N (none), E (even), O (odd)	N	For serial
MODBUS_STOPBITS	Serial stop bits	1	For serial
MODBUS_BYTESIZE	Serial byte size	8	For serial
MODBUS_TIMEOUT	Serial timeout (seconds)	1	For serial

Example .env File

For TCP:

MODBUS_TYPE=tcp
MODBUS_HOST=192.168.1.100
MODBUS_PORT=502
MODBUS_SLAVE_ID=1

For Serial:

MODBUS_TYPE=serial
MODBUS_SERIAL_PORT=/dev/ttyUSB0
MODBUS_BAUDRATE=9600
MODBUS_PARITY=N
MODBUS_STOPBITS=1
MODBUS_BYTESIZE=8
MODBUS_TIMEOUT=1

Usage

Installing for Claude Desktop

The configuration file:

{
   "mcpServers": {
       "Modbus MCP Server": {
           "command": "uv",
           "args": [ "--directory", "/path/to/modbus-mcp", "run", "modbus-mcp" ],
           "env": { "MODBUS_TYPE": "tcp", "MODBUS_HOST": "127.0.0.1", "MODBUS_PORT": 502 },
       }
   }
}

Using Tools

Note: Natural language support depends on the client’s ability to parse and map prompts to tools. The MCP Inspector requires structured JSON, but the examples below show how conversational inputs translate.

1. Read a Holding Register:

   • Prompt:

     Please read the value of Modbus holding register 0.
     

   • MCP Inspector JSON:

     {
       "tool": "read_register",
       "parameters": {"address": 0, "slave_id": 1}
     }

   • Expected Output: Value: <register_value>

2. Write to a Holding Register:

   • Prompt:

     Set Modbus holding register 10 to the value 100.
     

   • MCP Inspector JSON:

     {
       "tool": "write_register",
       "parameters": {"address": 10, "value": 100, "slave_id": 1}
     }

   • Expected Output: Successfully wrote 100 to register 10

3. Read Coils:

   • Prompt:

     Check the status of the first 5 Modbus coils starting at address 0.
     

   • MCP Inspector JSON:

     {
       "tool": "read_coils",
       "parameters": {"address": 0, "count": 5, "slave_id": 1}
     }

   • Expected Output: Coils 0 to 4: [False, False, False, False, False]

4. Write to a Coil:

   • Prompt:

     Turn on Modbus coil 5.
     

   • MCP Inspector JSON:

     {
       "tool": "write_coil",
       "parameters": {"address": 5, "value": true, "slave_id": 1}
     }

   • Expected Output: Successfully wrote True to coil 5

5. Read Input Registers:

   • Prompt:

     Read the values of 3 Modbus input registers starting from address 2.
     

   • MCP Inspector JSON:

     {
       "tool": "read_input_registers",
       "parameters": {"address": 2, "count": 3, "slave_id": 1}
     }

   • Expected Output: Input Registers 2 to 4: [<value1>, <value2>, <value3>]

6. Read Multiple Holding Registers:

   • Prompt:

     Get the values of Modbus holding registers 0 through 2.
     

   • MCP Inspector JSON:

     {
       "tool": "read_multiple_holding_registers",
       "parameters": {"address": 0, "count": 3, "slave_id": 1}
     }

   • Expected Output: Holding Registers 0 to 2: [<value1>, <value2>, <value3>]

License

This project is licensed under the MIT License. See LICENSE for details.