STM32 Web Programmer

Browser-based flash programmer for STM32 microcontrollers that expose the factory ROM bootloader over USB DFU. No drivers, no desktop software, no installation required.

Accepts: .hex (Intel HEX) or .bin files
Erases: only the flash sectors touched by the file — all other flash is left intact
Browser: Google Chrome (web), or the standalone Electron app (macOS / Windows / Linux)

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Device compatibility

The tool communicates using ST's DfuSe protocol over the standard ROM USB DFU bootloader (VID 0x0483 / PID 0xDF11). The flash sector map is read automatically from the DfuSe interface string descriptor, so any device that correctly exposes that descriptor should work without changes.

Tested

Device	Board	Result
STM32F723	Custom PCB	✅ Fully working

Expected to work

These devices share the same ROM bootloader protocol. They have not yet been independently validated — community reports welcome (see below).

Series	Example parts
STM32F2	F205, F207, F215, F217
STM32F4	F401, F405, F407, F411, F429, F446, F469
STM32F7	F722, F730, F745, F746, F756, F765, F767, F769, F777
STM32H7	H723, H743, H745, H750, H753, H755, H757
STM32L4	L433, L475, L476, L496 (USB-capable variants)
STM32G4	G431, G474, G491 (USB-capable variants)
STM32U5	U535, U545, U575, U585

Note: Only STM32 devices with a USB Full-Speed or High-Speed peripheral and a DFU-capable ROM bootloader are supported. Devices that use UART/I²C DFU or require a separate ST-LINK connection are not supported.

Report your device

If you have tested this tool on a device not listed above, please open a validation issue with your results. Reports help build a verified compatibility list for the community.

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Electron desktop app (recommended)

The Electron build runs as a native desktop app — no browser, no HTTP server, no Chrome required. USB device access is granted automatically.

Prerequisites

Node.js 18 or later — download from nodejs.org.

Install dependencies

cd /path/to/stm32-web-programmer
npm install

Run without building

npm start

Build installers

Build for your current platform only:

npm run dist:mac    # → dist/  (arm64 + x64 .dmg)
npm run dist:win    # → dist/  (.exe NSIS installer, x64)
npm run dist:linux  # → dist/  (.AppImage, x64)

Build all platforms at once (requires macOS for the mac target):

npm run dist

Output is placed in the dist/ folder.

macOS Gatekeeper warning: The app is unsigned. On first launch, right-click the .app inside the .dmg and choose Open, then confirm. Subsequent launches work normally.

Linux USB access: The AppImage needs permission to access USB devices without root. Create a udev rule once:

echo 'SUBSYSTEM=="usb", ATTR{idVendor}=="0483", ATTR{idProduct}=="df11", MODE="0666"' \
  | sudo tee /etc/udev/rules.d/49-stm32-dfu.rules
sudo udevadm control --reload-rules && sudo udevadm trigger

Replug the STM32 after applying the rule.

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Running in a browser (alternative)

If you prefer to use Chrome without installing Node.js, serve the files over a local HTTP server. WebUSB requires a secure context (localhost or https://) — opening index.html directly as a file:// URL will not work.

Can I just open index.html directly?

No. WebUSB requires a secure context — either https:// or localhost. Opening index.html as a file:// URL will show a "WebUSB not available" error. You must serve it through a local HTTP server (see below). No internet connection is needed; the server runs entirely on your machine.

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Starting the local HTTP server

Open a terminal, navigate to the project folder, and run the command for your OS.

macOS

Python 3 ships with macOS (10.15+):

cd /path/to/stm32-web-programmer
python3 -m http.server 8080

Linux

cd /path/to/stm32-web-programmer
python3 -m http.server 8080

If Python 3 is not installed: sudo apt install python3 (Debian/Ubuntu) or sudo dnf install python3 (Fedora).

Windows

Option A — Python (recommended if installed):

cd C:\path\to\stm32-web-programmer
python -m http.server 8080

Download Python from python.org if needed. Check "Add python.exe to PATH" during install.

Option B — PowerShell, no install required:

cd C:\path\to\stm32-web-programmer
$listener = [System.Net.HttpListener]::new()
$listener.Prefixes.Add("http://localhost:8080/")
$listener.Start()
Write-Host "Serving on http://localhost:8080 — press Ctrl+C to stop"
while ($listener.IsListening) {
    $ctx = $listener.GetContext()
    $file = Join-Path (Get-Location) $ctx.Request.Url.LocalPath.TrimStart('/')
    if (Test-Path $file -PathType Leaf) {
        $bytes = [System.IO.File]::ReadAllBytes($file)
        $ctx.Response.OutputStream.Write($bytes, 0, $bytes.Length)
    }
    $ctx.Response.Close()
}

Option C — Node.js (if installed):

cd C:\path\to\stm32-web-programmer
npx serve .

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Once the server is running, open Google Chrome and go to:

http://localhost:8080

Leave the terminal open while you use the tool. Press Ctrl+C to stop the server when done.

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Usage

1. Put the STM32 into DFU mode

The exact method varies by device, but the general approach is:

1. Pull BOOT0 high (connect to VCC via a solder bridge, switch, or jumper). Some boards have a dedicated BOOT button — hold it while resetting.
2. Reset the device (press the reset button or cycle power).
3. The STM32 enumerates as a USB DFU device — no firmware is running at this point.

Verify it is visible:

• macOS / Linux: lsusb → STMicroelectronics STM Device in DFU Mode
• Windows: Device Manager → Universal Serial Bus devices → STM Device in DFU Mode

2. Load a firmware file

Drag and drop a .hex or .bin file onto the drop zone, or click to browse.

• HEX files: target flash addresses are read automatically from the file.
• BIN files: enter the Flash address where the binary should be placed (default 0x08000000).

3. Connect the device

Click Connect Device.

• Electron app: the STM32 DFU device is selected automatically — no picker appears.
• Chrome browser: a USB device picker appears; select the STM32 DFU entry.

The device name and detected sector map appear on success.

4. Program

Click Program Flash. Progress is shown in three phases:

Bar	What it tracks
Erase	Sectors erased vs. total sectors to erase
Write	KB written vs. total KB
Verify	KB read back and confirmed (if enabled)

Options:

Checkbox	Default	Effect
Verify after write	On	Reads every written byte back and compares to the source
Leave DFU & reset	On	Triggers the bootloader to jump to 0x08000000 after programming

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Troubleshooting

Symptom	Cause	Fix
"WebUSB not available"	Opened as file:// in browser	Use the Electron app, or serve via http://localhost:8080 in Chrome
Device not listed in picker	Not in DFU mode	Check BOOT0 is high and reset the board
"Access denied" or "device in use"	Another tool has the device open	Close STM32CubeProgrammer, dfu-util, etc.
Verify mismatch	Write error or wrong target address	Check the hex/bin targets the correct flash region; retry
Device disconnects mid-write	USB cable or power issue	Use a short, quality cable; retry
"Cannot reach idle state"	Device stuck in error state	Disconnect, power-cycle the board, reconnect

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Hardware reference

Parameter	Value
USB VID	0x0483 (STMicroelectronics)
USB PID	0xDF11 (DFU ROM bootloader)
Transfer size	2048 bytes
Protocol	DFU 1.1 + ST DfuSe extensions

See PROGRAMMER.md for protocol details and the flash sector map.

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Copyright © 2026 DBML Group Inc. Released under the MIT License.