Web Serial Terminal

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serial monitor online

Online serial monitor in the browser

Plug the board in over USB, pick the baud rate the firmware uses and click Connect. The browser opens a dialog with the list of ports, and once you choose, whatever the board sends shows up at once, with the arrival time of each line.

What a browser monitor does and does not do

The Web Serial API lets a page open a serial port after you choose it in a browser dialog. When opening, the baud rate is required and the other parameters have defaults: 8 data bits, 1 stop bit, no parity and no flow control, the format known as 8N1. The API only works on a secure page (HTTPS) and needs a click to request the port, which is why the tool never connects by itself.
Support is limited. According to caniuse on 2026-11-02, it works in Chrome and Edge from version 89, in Opera from 76, in Firefox on desktop from 151 and in Chrome for Android from 156. Safari, iPhone, iPad, Firefox for Android and Samsung Internet lack the API. When the browser has no support, the tool shows that list instead of a button that does nothing.
On screen, incoming text is assembled into lines on LF, CRLF or CR, and each line carries the time of its first byte. The log keeps at most 5,000 lines or 8 MB, drops the oldest and can be saved as .txt or .csv. If the cable comes out, the tool records the loss and offers Reconnect. A monitor like this does not decode protocols or flash firmware: it shows and sends bytes.

Sends and speeds

Text with an LF line ending

Input: Hello + LF
Expected output: 48 65 6C 6C 6F 0A

Six bytes: five letters and the \n.

AT command with CRLF

Input: AT + CRLF
Expected output: 41 54 0D 0A

Modem modules usually expect CR or CRLF.

Bytes in hexadecimal

Input: 0x48 0x69
Expected output: 48 69 (Hi)

The 0x prefix is accepted.

Data ceiling at 9600 baud in 8N1

Input: 9600 baud, 8N1
Expected output: 960 bytes/s

10 bits per byte: 1 start, 8 data, 1 stop.

Full tool FAQ

What is Web Serial and which browsers have it?

It is an API that lets a page access serial ports with your permission. Per caniuse on 2026-11-02, it works in Chrome and Edge 89 or newer, Opera 76 or newer, Firefox on desktop from version 151 and Chrome for Android from 156. It does not work in Safari, on iPhone, in Firefox for Android or in Samsung Internet.

How do I connect an Arduino or an ESP board?

Which baud rate should I use?

What does 8N1 mean?

Why does it not work on iPhone, Safari or older Firefox?

Which line ending should I choose when sending?

How do I send bytes in hexadecimal?

Does the log grow without limit?

What if I pull the cable mid-session?

Is it safe? Does my data go to a server?

Frequently asked questions

Do I need to install a driver?

The browser only sees ports that the operating system already exposes. If the board uses a USB-serial converter the system does not recognize, install that converter maker's driver. If the port does not appear in the list, the tool cannot open it.

Why does the port list come up empty?

Almost always it is a charge-only cable with no data lines, or a missing driver. Swap the cable, try another USB port and check that no other program is holding the port.

Can I use it with Bluetooth or a network?

This tool talks to serial ports the operating system exposes, which includes virtual ports created by Bluetooth adapters already paired in the system. It does not open network or Bluetooth connections on its own.

Next steps

Continue in the tool

Open full tool

serial monitor online

Online serial monitor in the browser

What a browser monitor does and does not do

The Web Serial API lets a page open a serial port after you choose it in a browser dialog. When opening, the baud rate is required and the other parameters have defaults: 8 data bits, 1 stop bit, no parity and no flow control, the format known as 8N1. The API only works on a secure page (HTTPS) and needs a click to request the port, which is why the tool never connects by itself.

Support is limited. According to caniuse on 2026-11-02, it works in Chrome and Edge from version 89, in Opera from 76, in Firefox on desktop from 151 and in Chrome for Android from 156. Safari, iPhone, iPad, Firefox for Android and Samsung Internet lack the API. When the browser has no support, the tool shows that list instead of a button that does nothing.

On screen, incoming text is assembled into lines on LF, CRLF or CR, and each line carries the time of its first byte. The log keeps at most 5,000 lines or 8 MB, drops the oldest and can be saved as .txt or .csv. If the cable comes out, the tool records the loss and offers Reconnect. A monitor like this does not decode protocols or flash firmware: it shows and sends bytes.

Sends and speeds

Text with an LF line ending

Input: Hello + LF
Expected output: 48 65 6C 6C 6F 0A

Six bytes: five letters and the \n.

AT command with CRLF

Input: AT + CRLF
Expected output: 41 54 0D 0A

Modem modules usually expect CR or CRLF.

Bytes in hexadecimal

Input: 0x48 0x69
Expected output: 48 69 (Hi)

The 0x prefix is accepted.

Data ceiling at 9600 baud in 8N1

Input: 9600 baud, 8N1
Expected output: 960 bytes/s

10 bits per byte: 1 start, 8 data, 1 stop.

Full tool FAQ

What is Web Serial and which browsers have it?

How do I connect an Arduino or an ESP board?

Which baud rate should I use?

What does 8N1 mean?

Why does it not work on iPhone, Safari or older Firefox?

Which line ending should I choose when sending?

How do I send bytes in hexadecimal?

Does the log grow without limit?

What if I pull the cable mid-session?

Is it safe? Does my data go to a server?

Frequently asked questions

Do I need to install a driver?

Why does the port list come up empty?

Almost always it is a charge-only cable with no data lines, or a missing driver. Swap the cable, try another USB port and check that no other program is holding the port.