Given the number of possible USB-C cable combinations, it can be difficult to know whether the cable you have is actually optimal or even useful for whatever your current purpose. Is the pin usage mode 2.0, 3.0, Power Delivery? Using the wrong cable could result in sub-optimal data transmission speeds or some devices not working at all. A device developed by Peter Traunmüller features 25 LEDs to test for all possible combinations for USB-C receptacle pin usage, making it easy to determine what use cases a certain cable can support, from charging only to debug accessory mode and more.
So simple, why did this get made sooner? The C2C caberQU lights up as shown in this demo video, applying voltage to all pins of a cable to measure and indicate which are connected to the other end. This not only tells you supported modes, but can indicate broken pins. The device is a prototype, though in tests has been working as intended, and is available as a kit sold with one CR2032 battery, the PCB, and basic instructions — no soldering or difficult assembly required. No dedicated power supply is needed either, as all necessary power comes from the CR2032, which only discharges when a cable is connected. It is available for preorder via Traunmüller's Kickstarter campaign, while the BOM and documentation can be found on GitHub.