‹ Tools · Serial terminal
A serial monitor that lives in the browser
Connect a USB-serial board, pick a baud rate, and watch what it prints. Send lines back, view bytes as hex, save the log — no app to install. Works in Chrome, Edge, Opera or Firefox 151 or newer on a computer.
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Connection problems?
The browser is fine but the board does not show up, or the port will not open:
- Use a data USB cable (many phone charging cables carry no data) and try another USB port; on a hub, try the computer directly.
- Hold BOOT while plugging the board in so the chip enters its bootloader, then release it.
- Close anything else holding the port (Arduino IDE serial monitor, PlatformIO, a terminal, another tab of this page) and reconnect.
- Windows: the USB-serial bridge needs its driver — CH340, CP210x or FTDI, depending on the board. CH340, CP210x, FTDI
- Linux: add yourself to the serial group, then log out and back in:
sudo usermod -aG dialout $USER - macOS: no driver is needed for CP210x/CH340 on recent versions; if the port is missing, install the vendor driver above.
The formula
board TX → your RX, your TX → board RX, both ends agree on one baud rate
When to use it
Watching an ESP32 or Arduino boot log, debugging an AT-command modem, or checking a production unit on the bench without opening a separate serial app. It talks to the port with the browser’s own Web Serial API — the same permission prompt as the ESP32 and STM32 flashers on this site.
Pitfalls
- No ports listed? Try another USB cable (many are charge-only) and check the board’s USB-serial chip driver (CP210x, CH340, FTDI) is installed.
- "Failed to open the serial port" or permission errors mean another program already holds the port — close it, or unplug and replug the board.
- Garbled text almost always means the wrong baud rate, not a bad cable — try the board’s usual rate first (115200 is the most common default) before anything else.
- Only one program can hold a serial port at a time. Close the Arduino IDE’s monitor, PlatformIO, or another tab of this page before connecting here.
- "Reset on connect" pulses DTR/RTS the way esptool and the Arduino IDE do; pick the profile for the chip on the board, or "None" if the board should keep running undisturbed.
- Nothing you send or receive leaves this computer — there is no server in the middle. The usage statistics below only ever record which baud rate was picked and which buttons were used, never the data itself.
Related note
Browser-based firmware flashing without an installerNeed a production test fixture built around a serial port like this one?