Frequently asked questions

A serial terminal for Windows and Linux, built for embedded and IoT development, with a built-in MCP server. You get color-coded trace levels, a 24-field live dashboard, quick commands with hotkeys and JavaScript scripts. AI coding agents such as Claude Code can use it to read the trace and dashboard, send commands to your device and set up connections.

No. Termethos is a complete serial terminal on its own, and the MCP server is off until you turn it on. You can use it just for its trace, dashboard and commands, and turn agents on later.

Termethos has setup instructions for Claude Code, Cursor and VS Code. Other MCP clients work too if they can connect to an MCP server over Streamable HTTP and send an Authorization header.

The Model Context Protocol is an open standard that lets AI agents use tools and data outside the chat. Termethos runs an MCP server, so an agent can call tools such as read_trace, read_dashboard and send_command on the connection you have open. See all tools

Any device that shows up as a serial port, a COM port on Windows or /dev/ttyUSB… or /dev/ttyACM… on Linux, directly over USB or through a USB-to-serial adapter. That includes ESP32, ESP8266, STM32 (through an ST-LINK virtual COM port or a USB-UART adapter), RP2040 and RP2350, Arduino boards and most other microcontrollers. You can add custom baud rates, such as 74880.

Yes. Pick a port and baud rate, connect, read the output and type commands. The trace levels, dashboard and quick commands are optional extras that work with the printf() output you already have.

Yes. It runs inside Termethos on your computer, listens only on 127.0.0.1 and needs a token for every request, so other computers can't reach it. Termethos doesn't send your serial data anywhere. Keep in mind that the AI agent you connect sends what it reads to its own model provider, as it does with the rest of your code.

A license key for two computers, for a one-time payment. It includes all 2.x updates, and there's no subscription, so nothing renews. Without a license Termethos runs in simulation mode for free, with a simulated device, so you can try the app and your AI agent before you buy.

It calls disconnect to free the port, flashes with your project's build tool, then calls connect and waits for the boot message. Allow connecting and disconnecting in the AI agents dialog. How the loop works

Yes, when you check Allow creating and changing connections. Agents can add a connection and set its port, baud rate, data bits, parity, stop bits, flow control, DTR and RTS, and change those settings later. With Allow connecting and disconnecting they can also switch between connections and open them.

Yes. In the AI agents dialog, uncheck Allow sending commands and running quick commands, and leave scripts, connecting and editing connections off. Agents can then read the trace, dashboard, connections and quick commands.

Commands sent by agents appear in the command history as [agent] <command>, and the MCP item in the status bar turns green while an agent is using Termethos.

Yes. In simulation mode agents work with the simulated trace and dashboard, so you can set up and test your agent. Activate a license and they work with your real board.

Windows and 64-bit (x86-64) Linux. On Linux it's built and tested on Ubuntu 22.04, and runs on newer Ubuntu releases and on Debian-based distributions of the same age or newer. It doesn't run on Ubuntu 20.04 or older. One license covers both systems. Download

This is expected, because the Termethos app isn't digitally signed (signing is an expensive process). The warning should go away as more users download and install it.

Nothing, your license stays activated. Since version 2.0 it's kept outside the install folder, so installing a new version or reinstalling doesn't touch it.

On Windows the app is usually in %localappdata%\Programs\termethos, and on Linux the .deb installs it in /opt/Termethos. Your settings and license are in %APPDATA%\Termethos on Windows and ~/.config/Termethos on Linux.

Download the .deb, which is for Ubuntu, Debian and their derivatives. Install it with sudo apt install ./termethos_<version>_amd64.deb (not dpkg -i), so the libraries it needs are installed too. It adds a menu entry and the termethos command.

On Linux, serial ports belong to the dialout group. Add yourself once with sudo usermod -aG dialout $USER, then log out and back in. On Arch, Manjaro and some other distributions the group is uucp instead.

USB-serial adapters (CH340, CP210x, FTDI) show up as /dev/ttyUSB0, /dev/ttyUSB1 and so on, and boards with native USB (Arduino Uno, Raspberry Pi Pico, ESP32-S3, ST-LINK) as /dev/ttyACM0. The /dev/ttyS… entries are built-in UARTs that most PCs don't have. If a CH340 board appears and disappears right away on Ubuntu 22.04, remove brltty with sudo apt remove brltty unless you use a braille display.

Yes. Copy termethos.json from %APPDATA%\Termethos to ~/.config/Termethos or back, and change the port names, such as COM4 to /dev/ttyUSB0.

Go to github.com/bluephoton/termethos-app/issues and click New issue. Include as much detail as you can, such as your Termethos version and the steps that reproduce the problem.

Hover over the application icon in the top-left corner of the app window. The version appears as a tooltip.

A license key for two computers, such as your bench PC and your laptop, for a one-time payment. It includes all 2.x updates, and there's no subscription, so nothing renews or charges you again.

Polar is our reseller. It runs the checkout, takes the payment, sends your receipt and license key, and handles sales tax and VAT. We never see your card details. Any tax for your country is shown at checkout before you pay.

Polar emails your receipt within a few minutes. Your license key is in your Polar customer portal: sign in with the email you paid with. Still missing? Contact admin@termethos.com.

Open Termethos, paste your license key into the banner at the top and click Activate. All features unlock right away, without a restart.

Only to activate. After that it works offline. When it's online it checks the key again about once a month, and if it can't reach the server it simply keeps working. If you chose to share anonymous usage data, that is sent only while you're online; offline, nothing is queued or lost.

Your license key and your computer's name, sent to Polar to register the activation. Nothing about your devices or serial data is sent. Activation is separate from anonymous usage data, which is sent only if you agree to it (see below).

Only if you agree. On the first start Termethos asks whether to share anonymous usage data, and nothing is sent until you answer. If you untick Share anonymous usage data, nothing is ever sent. You can change your choice any time with Usage data in the status bar at the bottom of Termethos. Your choice is kept in usage-data.json in the same folder as the license.

Which features are used (connecting and the baud rate, the dashboard, quick commands, scripts, session export, AI agent settings, MCP tool calls and the name of the AI agent that connects), whether license activation succeeded, and the kind of errors that happen, never their message. Each event carries the time, a random session id that changes after an hour without use, the Termethos and operating system version, your language setting and the Chromium version. It goes to Aptabase, a privacy-friendly analytics service, which works out your country from the connection's IP address. Never sent: port names, commands, scripts, serial or dashboard data, error messages, your settings, your license key, or your user or computer name. There's no device or user id, so events can't be tied to you or your computer.

Each license key can be active on two computers at a time. For more computers you need another key. That said, feel free to contact us if you want a free license. We usually say yes!

If your key is already active on two computers, first click Deactivate this computer in the status bar at the bottom of Termethos on the one you no longer use, then activate your key on the new one. If the old computer is gone or its system was reinstalled, email admin@termethos.com with your license key and we'll free it up. Either way, you don't need to buy a new license.

In %APPDATA%\Termethos\license.json on Windows and ~/.config/Termethos/license.json on Linux. Copying it to another computer won't activate that computer.

The configuration file is %APPDATA%\Termethos\termethos.json on Windows and ~/.config/Termethos/termethos.json on Linux. Be careful, because errors in this file can make the app unusable. It's always a good idea to back it up before you change it.

If you want the basic editor back for any reason, set this flag to false in your advanced settings:

{
  ...
  "ui": {
    "richAdvancedSettings": false
  }
  ...
}

Open the advanced settings by clicking the red cog icon on the toolbar. Then carefully add your custom baud rate to the list, as in this example:

...
"serial": {
  ...
  "baudrates": [
    ...
    74800,
    74880,
    115200,
    ...
  ]
  ...
}
...

You can turn this on in the advanced settings like this:

{
  ...
  "ui": {
    ...
    "fullClear": true,
    ...
  }
  ...
}

Make sure you're clicking, not dragging! This can happen if the mouse moves slightly between press and release. Oh well! ☺

You can carefully edit the advanced settings to create a command that runs a custom script. Scripts get the serial port, so they can write data to it and set its DTR and RTS lines. Termethos asks before a script runs the first time. See Scripts for more examples. Here's an example command:

{
  "command": "reset",
  "description": "Fancy script command",
  "hotKey": "alt+5",
  "name": "My Command",
  "script": "(port) => { port.write('something') }"
}