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.
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| 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
- 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.
- Find the port:
uvx labmcp ports
- Test the connection:
uvx labmcp-mettler-toledo --address /dev/ttyUSB0 --check
uvx labmcp-mettler-toledo --address /dev/tty.usbserial-XXXX --check
uvx labmcp-mettler-toledo --address COM4 --check
uvx labmcp-mettler-toledo --address tcp://192.168.1.60:8001 --check
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).
| Tool | Kind | Description |
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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 |
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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