From the website copy:

Know what your USB-C cable can really do.

WhatCable explains cable speed, charging limits, e-marker data, and connected devices in plain English. Name a cable and it tracks how the cable actually performs over time, so you can spot the one that has started misbehaving. No more guessing why a cable charges slow or refuses to drive your display.

I tend to purchase cables from either Apple or B&H Photo Video because I am mistrusting of the sourcing from sellers on Amazon and Best Buy. Though I may try some cheaper brands now that I can test their quality with this neat little tool.