While Raspberry Pi single-board computers are generally fantastic, one frustration with them (besides availability) is that the GPIO pins are unlabeled. This can leave you guessing and/or searching for documentation. The Blinky RPi Header from EK ENG takes care of the (labelling) problem as a plug-in diagnostics board, providing not only printed labels, but indicator LEDs to show what each pin is doing.
It’s quite a clever setup–classed as a “headband” by its creator–as it’s too small to be a HAT, and not the same format as a pHAT. The device doesn’t use any pull-up or pull-down resistors, and each LED has its own MOSFET driver, allowing LED current to be supplied from the Pi’s 5V rail. The result is that adding one of these shouldn’t interfere with GPIO functionality, even protocols like I2C and SPI. After all, if your diagnostic tool is causing the problem, then it’s really not useful whatsoever.
The device would be excellent for visualizing the state of different buttons, switches, and whether or not a pin is quickly sending data, helping to identify a problem with minimal poking around. Once things are in a working state, you can then remove the blinky for use on another project, or leave it on as a glorious blinkenlights display!