Flash a Raspberry Pi Pico: BOOTSEL button and UF2 drag-and-drop (C or MicroPython)

Every Pico has a USB bootloader in ROM. You don't need any special tool for the first flash.

Procedure

1. Hold the BOOTSEL button, then plug the Pico into your computer via USB. Release the button.
2. The Pico appears as a USB drive: RPI-RP2 (RP2040 boards) or RP2350 (Pico 2 boards).
3. Copy a .uf2 file onto that drive. The drive disappears and the Pico reboots into the new program.

Where the UF2 comes from

• Your own C/C++ program: the Pico SDK writes name.uf2 next to name.elf when your CMakeLists.txt calls pico_add_extra_outputs(name).
• MicroPython: download the UF2 for your exact board from micropython.org (separate builds for Pico, Pico W, Pico 2, Pico 2 W). Then connect to the REPL over USB serial, e.g. with Thonny.
• Quick hardware test: Raspberry Pi publishes "universal" blink and hello-world UF2 files that run on all Pico variants (linked from the documentation).

Tips

• Use the MicroPython build for your exact board; the builds differ per board (for example in wireless support on the W models).
• Tired of unplugging to press BOOTSEL? Use picotool with -f on a running SDK program with USB stdio, or a Debug Probe to flash over SWD (see those items).
• The ELF file is what a debugger loads; the UF2 is only for the USB bootloader.