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esptool · command line

Fix “Could not connect to an Espressif device on any of the 1 available serial ports”

esptool was run without --port and couldn't find an ESP on any port. Give it the port explicitly, put the board in download mode, and check the driver.

ESP32ESP8266ESP32-S3ESP32-C3ESP32-CAMUpdated 3 Nov 2026

Community draft — report a mistake

What you see

OutputOutput
> esptool.py --chip esp32 erase_flash
esptool.py v4.8.1
Found 1 serial ports
Serial port COM1
Connecting......................................

COM1 failed to connect: Failed to connect to ESP32: No serial data received.
For troubleshooting steps visit: https://docs.espressif.com/projects/esptool/en/latest/troubleshooting.html

A fatal error occurred: Could not connect to an Espressif device on any of the 1 available serial ports.

When you run esptool without --port, it scans every serial port on the computer and tries to connect to each. This message is the summary after all of them failed. Often the board’s own port wasn’t in the list at all.

Read the lines above it. If your board’s port isn’t listed, fix the cable or driver. If it is, pass it with --port and hold BOOT while connecting.

Quick fix — try in order

  1. 1

    Look at which ports it tried

    “Found 1 serial ports … COM1” means your board's port wasn't even in the list — COM1 is usually the PC's built-in serial port. Fix the cable or driver until a new port appears when you plug in.

  2. 2

    Pass the port explicitly

    esptool.py --port COM5 --chip esp32 erase_flash (Linux: --port /dev/ttyUSB0). Copy commands from MicroPython's download page and add --port.

  3. 3

    Hold BOOT while it says Connecting

    If the right port was tried but failed, the chip didn't enter download mode. Hold BOOT (IO0) until “Chip is …” appears.

  4. 4

    Close anything holding the port

    Thonny, Arduino Serial Monitor or a browser tab can keep the port busy so the scan skips or fails it.

Why it happens

Why did esptool scan ports at all?

Without --port, esptool tries every serial port it finds. The final message only summarises — read the per-port lines above it for the real reason.

Many ports listed (Bluetooth, modems)

Laptops often expose Bluetooth serial ports that take seconds each to time out. Passing --port skips them.

MicroPython and Thonny users

Thonny's “Install or update MicroPython (esptool)” dialog asks for the port; pick the one that appears when you plug the board in.

Board-specific notes

ESP32-S3 / C3 (native USB): Hold BOOT and tap RESET first; the port that appears is the one to pass with --port.

Drivers — official sources only

CP210x (Silicon Labs)silabs.comCH340 / CH341 (WCH)wch-ic.com

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