Advanced serial terminal

The serial terminal for people who write firmware

Debug, monitor and control your device from one window. Termethos turns plain printf() output into leveled logs and a live dashboard, and gives you commands, hotkeys and scripts for the actions you repeat all day. It works on its own, and it's the same view your AI agent gets over MCP.

Download Termethos UI tour

Trace

Logs you can read at full speed

Prefix a line with !I, !W or !E and it's shown as info, warning or error, without remembering ANSI escape codes. ANSI colors work too.
!# draws a box around text, for a firmware version or the start of a boot.
Alternating line shading and error highlighting make the important line stand out.
Up to 50,000 lines are kept by default, each with its receive time. Pause the trace or lock scrolling while you read.

Trace markup reference

Termethos trace with a plain line, an info line in blue, a warning line in orange and an error line highlighted in red

Telemetry dashboard

Live values without writing a GUI

Print @{11:123} and field 11 shows 123. Values update in place, so the trace stays clean.
24 fields in a 3 × 8 grid, for sensor readings, state machines, counters or anything that changes.
The field that changed last is highlighted, so you notice a change even in a busy session.
Hide the dashboard to make room for the trace, or reset every field in one click.

Dashboard how-to

Termethos dashboard fields, with the field that changed last highlighted in yellow

Commands

A command line, quick commands and hotkeys

Talk to your firmware's shell from the command line. Sent commands stay in the history, so you type less.
Quick commands become buttons on the side, each with an optional hotkey, like space to stop the motors.
Quick commands live in the advanced settings, so you can share the file and your team gets the same buttons.

Take the UI tour

Annotated Termethos window showing the command line, command history, quick command buttons, trace and dashboard

JavaScript scripting

Scripts for what a plain terminal can't do

A quick command can run a JavaScript function that gets the serial port.
Send a test sequence with pauses, or raw bytes for a binary protocol, without the line ending.
Set the DTR and RTS lines, for example to reset an ESP32 or Arduino.
Termethos shows a script and asks before it runs the first time, and again if it changes.

Scripting guide

quick command script

// send a test sequence, 250 ms apart
async (port) => {
  for (const cmd of ["motor 1 200", "motor 2 200", "log on"]) {
    await port.write(cmd + "\r\n");
    await new Promise(r => setTimeout(r, 250));
  }
}

Connections and sessions

Built for long sessions on real boards

Saved connections

A profile per board: port, baud rate and line settings. Switch in one click and edit it when your setup changes.

Custom baud rates

Standard rates plus your own, such as 74880 for ESP8266 boot messages. How

DTR and RTS control

Choose the DTR and RTS state when the port opens, so connecting doesn't reset your Arduino.

Automatic reconnect

When the board resets or you re-plug it, Termethos reconnects by itself.

Session export

Save the trace, field changes and commands with millisecond times, as .log text or .jsonl for scripts.

Copy for AI

Copy a Markdown summary of the connection, dashboard, recent trace and commands, to paste into any AI chat.

Simple by default

The window starts simple and shows advanced options when you need them.

Advanced settings

Every setting in one JSON file with a rich editor, checked before it's applied.

Ready for AI agents

Turn on the built-in MCP server and your agent sees the same trace and dashboard. MCP server

Try the terminal free

Download Termethos and try every feature in simulation mode, no board needed. A one-time $24.50 license unlocks real serial ports.

Download Termethos Buy $24.50