AVR / Arduino Uploader

About this tool

This is a browser-based avrdude for classic AVR boards: pick your board, drop in a compiled .hex, and it talks the STK500 protocol straight to the board's bootloader over the Web Serial API — no Arduino IDE, no toolchain, no driver install on a modern OS. Everything runs locally in Chrome or Edge; the file you drop and the bytes read back from the chip never leave your machine.

It is built for the boards most people actually have on the bench — the Arduino Uno, Nano and Pro Mini (ATmega328P) and the Mega 2560/1280 — and it is honest about the rest. AVR uploading is genuinely fiddly (mixed protocols, mixed USB bridges, mixed baud rates, and a real risk of bricking a chip with the wrong fuse), so this tool states plainly which paths are implemented and which are untested, and gates every dangerous operation behind a deliberate confirmation.

How the upload works

When you click Connect, the browser opens the serial port at the board's upload baud, then pulses the DTR/RTS lines to reset the board into its bootloader — the same trick the Arduino IDE uses, because DTR is wired through a capacitor to the chip's RESET pin. The tool then syncs with the bootloader, reads the 3-byte device signature to confirm the chip matches the board you picked, and programs the .hex one flash page at a time with a live byte-and-percent progress readout. After writing, it reads the flash back and compares it byte-for-byte against your file, so a successful upload really means the chip holds exactly what you sent.

Which boards actually work, and the CH340 vs FTDI vs native-USB divide

The Uno, Nano and Pro Mini use the STK500v1 protocol (Optiboot); the Mega 2560/1280 use STK500v2. Both are implemented here, but note the honesty matrix below: nothing has been verified against real silicon by the author, so treat every board as untested until you confirm it. The other variable is the USB-to-serial bridge. A genuine Uno/Mega uses an ATmega16U2 and needs no driver. Cheap Nano/Pro-Mini clones use a CH340, which needs a driver on older systems but works out of the box on current macOS, Linux and Windows. FTDI-based boards are similar. Native-USB boards like the Leonardo/Micro (ATmega32U4) are a different animal entirely — the sketch and the bootloader appear as two separate USB devices, and the 1200-baud reset re-enumerates a brand-new port that Web Serial cannot follow without a second device picker, so the Leonardo is listed as unsupported rather than given a flaky path.

Brick risk and recovery

Flashing a sketch over the bootloader is safe and reversible — worst case you re-flash. Writing fuses is not: the wrong clock, reset-disable or SPI-enable fuse can make the chip unreachable over serial, recoverable only with a high-voltage or ISP programmer. This tool reads and decodes fuses for you by default, but fuse writing is off, hidden behind a double confirmation, and clearly labelled brick-risk. Burning a bootloader onto a bare chip needs an ISP programmer and is out of scope for a serial-only tool; if your board has no working bootloader, flash the ArduinoISP sketch onto a second good board and use that — the firmware menu links the sketch and the notes explain the wiring.