Mettler Toledo Balance — MCP Server

Let an AI agent weigh samples, tare containers, log drift and evaporation, run internal adjustments and drive the draft shield on Mettler Toledo balances through the open MT-SICS interface command set.

Try it without hardware

uvx labmcp-mettler-toledo --simulate --check

Connect your balance

1. Balance setup: in the balance menu, set the interface (RS232/USB/Ethernet) to MT-SICS (sometimes called "Host" or "Dialog"). Factory settings are 9600 baud, 8 data bits, no parity, 1 stop bit, Xon/Xoff.
2. Find the port: uvx labmcp ports
3. Test the connection:

   uvx labmcp-mettler-toledo --address /dev/ttyUSB0 --check          # Linux
   uvx labmcp-mettler-toledo --address /dev/tty.usbserial-XXXX --check  # macOS
   uvx labmcp-mettler-toledo --address COM4 --check                  # Windows
   uvx labmcp-mettler-toledo --address tcp://192.168.1.60:8001 --check  # Ethernet
   

   Non-default settings go in the address: serial://COM4?baudrate=19200&xonxoff=false.

Add to your MCP client

Claude Code

claude mcp add balance -- uvx labmcp-mettler-toledo --address /dev/ttyUSB0

Claude Desktop / Cursor / Windsurf (claude_desktop_config.json, .cursor/mcp.json, …)

{
  "mcpServers": {
    "balance": {
      "command": "uvx",
      "args": ["labmcp-mettler-toledo", "--address", "/dev/ttyUSB0"]
    }
  }
}

Add --read-only to allow weighing but block taring, zeroing and door movement. For other clients, generate the snippet with uvx labmcp config mettler-toledo --address /dev/ttyUSB0 --client vscode (also cursor, codex, claude-code).

Tools

get_connection_info, get_command_log and reconnect are built into every LabMCP server.

Safety limits

Override at launch: --limit max_series_duration_s=3600. Whatever the limit says, a single series is capped at one hour (the tool's time limit).

Example prompts

• "Tare the balance, then tell me when the reading is stable after I add the sample."
• "Log the weight every 10 s for 5 minutes and tell me the evaporation rate in mg/min."
• "Weigh out ~250 mg: tell me how much more to add, reading every few seconds, until I'm within ±2 mg."
• "Run an internal adjustment and confirm it succeeded before we start the calibration curve."

Notes

• read_weight(stable=True) sends S, which waits for stability. If the balance cannot settle (draughts, vibration), it returns S I. The server reports this as an error, so retry or use stable=false.
• Weights are in the balance's unit 1 (normally grams). Units shown on the display (unit 2) don't affect the interface.
• Draft-shield (WS) and temperature (M28) commands exist only on balances with that hardware; other balances answer ES/L, which the server reports clearly.
• run_internal_adjustment waits for the final C3 A without blocking the connection: reset_balance aborts a running adjustment, and other commands are refused until it ends (their replies would be mixed up with the result).
• Before each command the server discards anything the balance sent unasked (e.g. a print-key transmission) and checks that the reply belongs to the command, so one late reply cannot shift every later reply by one.
• show_message accepts printable ASCII only, and set_tare_preset only a unit symbol: a line break would otherwise reach the balance as a second MT-SICS command.

Hardware verification