CoolTerm is a free, native macOS application for communicating with hardware devices over serial connections — the go-to tool for embedded engineers, electronics hobbyists, and anyone who needs to talk directly to a microcontroller, Arduino, Raspberry Pi, or custom circuit board.
What is CoolTerm?
CoolTerm is a lightweight serial port terminal emulator for macOS (and Windows/Linux) that lets you send and receive raw data over RS-232 and USB-serial connections. Created and maintained by Roger Meier as free, donationware software, it has been a trusted staple of the hardware-development community for well over a decade. Unlike browser-based or IDE-bundled serial monitors, CoolTerm is a dedicated tool — and that singular focus shows in every detail of the interface.
The moment you plug in a device, CoolTerm lists the available ports and lets you configure baud rate, data bits, stop bits, parity, and flow control through a clean settings panel. There's no hunting through menus: the connection dialog is front and centre, and you're usually talking to your hardware within thirty seconds of launching the app.
What does CoolTerm do best?
CoolTerm shines at the things serial-terminal work actually demands: rock-solid connection handling, flexible data display, and reliable logging. The receive display can toggle between plain ASCII and hex on the fly — indispensable when you're debugging a binary protocol and need to see both the human-readable characters and the raw bytes side by side. The connection sequence and string transmission features let you automate repetitive send-cycles, which is a genuine time-saver when you're resetting firmware or walking a device through an initialisation routine dozens of times a session.
Logging is where CoolTerm quietly outperforms the Arduino IDE's built-in serial monitor. You can write incoming data to a timestamped file with a single click, and the app keeps writing even when you scroll back through the buffer — no dropped bytes, no pauses. For any project where you need an audit trail of device output, this alone justifies installing CoolTerm.
- Multi-connection support: open several port windows simultaneously — critical when you're debugging two devices talking to each other.
- Line-mode and raw-mode: send complete strings terminated by your choice of CR, LF, or CR+LF without fighting a single-character-at-a-time input box.
- Connection options file: save your baud rate, port, and display settings per project so re-opening a familiar device takes one double-click, not five config steps.
- Hex send: paste raw hex sequences for protocols that demand it — SPI sniffers, custom bootloaders, proprietary hardware.
Is CoolTerm free?
CoolTerm is completely free to download and use. Roger Meier distributes it as freeware through his personal site at freeware.the-meiers.org, with no feature limits, no trial period, and no account required. The project accepts voluntary donations, which is a fair ask for software this polished and actively maintained. I dropped a few euros his way after my first week — it felt wrong not to.
Who should use CoolTerm?
If you work with embedded hardware on a Mac, CoolTerm belongs in your dock. Arduino and ESP32 developers will find it more capable than the IDE's monitor. Electrical engineers debugging UART or RS-232 peripherals get the hex view and logging they rarely find elsewhere for free. Students building their first microcontroller project appreciate the approachable UI compared to command-line tools like screen or minicom. Even network engineers testing serial-console access to routers and switches will find it snappier than a PuTTY session run through XQuartz.
It is probably overkill for someone who only needs serial access twice a year — the macOS built-in screen command handles casual one-off connections fine. But for anyone doing regular hardware work, the saved connection profiles and logging alone make CoolTerm a permanent fixture.
What are the best CoolTerm alternatives?
The honest alternatives depend on your exact workflow. Serial (by Decibel Eleven) is a polished paid option with a more modern macOS UI, better Apple Silicon polish, and SSH-over-serial — worth the price if you want something that feels fully native to the current design language. ZTerm is a classic freeware option but feels unmaintained by comparison. GNU screen and minicom cover the command-line crowd who never want to leave the terminal. For pure Arduino work, the PlatformIO IDE's serial monitor is adequate but not as flexible for non-Arduino targets. CoolTerm sits in the sweet spot: feature-rich, free, and maintained.
