Mettler Toledo Balance

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.

Package	labmcp-mettler-toledo
Instruments	Excellence XPR/XSR, XP/XS, XA/XE, MS/ML, NewClassic ME/MS, and other MT-SICS balances and weighing terminals
Interfaces	RS-232, USB (virtual COM port), Ethernet (XPR/XSR, or any serial-to-Ethernet adapter)
Protocol	MT-SICS levels 0–2 (reference manual)
Status	🧪 simulated: tested against a wire-level MT-SICS simulator, not yet verified on hardware. Report a hardware test

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

Tool	Kind	Description
clear_tare	🎛 control	Clear the tare memory (tare = 0).
get_command_log	👁 read	Return the most recent raw commands sent to / replies received from the instrument (newest last). Useful for debugging and for recording what was done.
get_connection_info	👁 read	Report which instrument is connected (identity, address, simulated or real), whether the server is read-only, and the active safety limits. Call this first.
get_draft_shield	👁 read	Report the position of the motorised draft-shield doors (Excellence/XPR balances only).
get_tare	👁 read	Return the weight currently stored in the tare memory.
log_weight_series	👁 read	Record a series of immediate (unfiltered) readings to monitor drift, evaporation, moisture uptake or stabilisation. Returns every reading plus summary statistics.
read_temperature	👁 read	Read the balance's internal temperature probe(s) in °C (MT-SICS M28, if supported).
read_weight	👁 read	Read the current net weight from the balance.
reconnect	🛑 safety	Close and re-open the connection to the instrument (e.g. after it was power cycled or a cable was re-plugged).
reset_balance	🛑 safety	Abort whatever the balance is doing (an adjustment, a repeating weight stream, a pending command) and reset it to its power-on state without zeroing (MT-SICS @). Clears the tare. Motorised draft-shield doors have their own obstruction detection and reverse if blocked.
run_internal_adjustment	🎛 control	Adjust (calibrate) the balance with its built-in reference weight (MT-SICS C3). The pan must be empty and the balance undisturbed. Takes roughly 1-3 minutes.
set_draft_shield	⚠️ hazard	Open or close the motorised draft-shield doors. Make sure nothing (and no one's fingers) is in the way of the doors.
set_tare_preset	🎛 control	Preset a known tare weight (e.g. a container weighed earlier).
show_message	🎛 control	Show a short message on the balance display (e.g. 'Add sample 3'). Use show_weight_display to return to the normal weight display.
show_weight_display	🎛 control	Switch the balance display back to showing the weight.
tare	🎛 control	Tare the balance: store the current load (e.g. an empty container) as the tare weight. Returns the stored tare weight.
zero	🎛 control	Zero the balance with the current load. Also clears the tare memory.

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

Safety limits

Limit	Default	Meaning
max_series_duration_s	600 s	Longest weight-logging series an agent may start

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

Model	Firmware	Interface	Verified by	Date
none yet: be the first