at-mcp

A native Python MCP server for talking to cellular modems and radio modules via AT commands over a serial port (pyserial). It lets LLM agents enumerate serial ports and run read-only diagnostics: modem identity, IMEI, signal quality, network registration.

AT commands are publicly standardized in 3GPP TS 27.007 (plus TS 27.005 for SMS), so this project contains no proprietary or GPL code. It is the serial-port sibling of sahara-mcp and follows the same design.

ALPHA — NOT TESTED. This server is not tested against real modems. The result-code decoders follow the 3GPP spec but have not been validated on hardware. Use at your own risk, treat output sceptically, and start with a USB dongle you don't mind restarting.

Features

• at_list_ports — enumerate serial COM/ACM ports visible to pyserial

• at_command — send any AT command, return raw result lines (guarded to AT / AT+ prefixes)

• at_info — ATI (manufacturer/model/rev) + AT+CGMR

• at_identity — AT+CGSN (IMEI), AT+CGMI, AT+CGMM

• at_signal — AT+CSQ (RSSI/BER) decoded; merges AT+CESQ if supported

• at_network — AT+COPS? operator + AT+CREG?/AT+CGREG? registration state (home/roam/searching/denied/unknown/not registered)

• at_power — AT+CFUN=0 / AT+CFUN=1 to toggle the radio (opt-in; this is the only tool that changes device state)

Related MCP server: UART MCP Server

Finding the modem's COM port

Windows Device Manager:

1. Press Win+X → Device Manager.

2. Expand Ports (COM & LPT) — the modem usually appears as "USB-SERIAL CH340 (COM3)", "USB-SERIAL CP210x (COM5)", "Standard Serial over Bluetooth link (COM7)", or the modem vendor's own name.

3. The COM number in parentheses is the port argument (e.g. COM3).

USB dongles / radio modules (SIM7000/SIM7600, Quectel EC25/BG96, Sierra, u-blox, etc.): plug the module in, note the new port that appears under Ports (COM & LPT), and set a matching baud rate (115200 is the typical factory default). If no port appears, you may need the vendor USB driver or a USB‑to‑TTL adapter for bare radio modules.

Install

pip install -e .

This pulls in mcp and pyserial.

Usage

Start the MCP server and point an MCP client (e.g. opencode, Claude Desktop) at it:

python -m at_mcp_server          # stdio transport

Example tool calls:

at_list_ports()
at_info(port="COM3")
at_identity(port="COM3")
at_signal(port="COM3")
at_network(port="COM3")
at_power(port="COM3", state="off")   # drops calls/data!
at_power(port="COM3", state="on")

Reference

• 3GPP TS 27.007 — AT command set for User Equipment (RTTI / AT+CSQ, AT+COPS?, AT+CREG?, AT+CGSN, AT+CFUN, …)

• 3GPP TS 27.005 — SMS AT commands

License

GPL-3.0. Copyright (c) 2026 libertyrights. All code here is original; AT command semantics come from the public 3GPP specifications.