ESP32 flasher that checks before it writes

The formula

file chip id = connected chip · chip revision ≥ minimum in the file · offset + size ≤ flash fitted · MD5 read back after writing

When to use it

Loading a release build onto a dev board, re-flashing a batch of boards on the bench, or handing a customer a page that flashes their device without a Python install. It uses Espressif’s own esptool protocol through the browser’s serial port, so it behaves like esptool.py: same chip detection, same flash-size detection, same stub, same MD5 check.

Pitfalls

• A .bin is either an app (flashed at 0x10000) or a merged image with bootloader and partition table (flashed at 0x0, or 0x1000 on ESP32 and ESP32-S2). The page reads the partition table to tell them apart, so you never pick the offset by hand.
• The chip id, minimum chip revision and flash-size field come from the image header ESP-IDF writes into every build. A file built for ESP32-S3 has chip id 9; an ESP32-C3 reports 5. That comparison is exact, not a guess from the file name.
• Flash mode (QIO/DIO) cannot be read back from the board, so a mismatch shows as a note, not a block. If a board reboots in a loop after flashing, rebuild with DIO.
• Erase-all wipes NVS, Wi-Fi credentials and any factory calibration you stored yourself. It is off by default and needs its own confirmation.
• Nothing leaves your computer: the file is parsed in the page and written straight to the port. The approved-hash list lives in this browser only.

Related note