WhatCable turns your Mac into a professional USB-C diagnostic tool

The software functions by pulling information already collected by the Mac’s port controller during USB Power Delivery negotiation. While Apple’s firmware routinely exchanges structured identity messages with e-marked cables, this technical data is typically buried deep within the system registry. Developer Darryl Morley designed the app to bridge this gap, using public APIs to extract vendor IDs, voltage limits, and active versus passive cable designations without requiring invasive root access or private entitlements.

Beyond reading e-marker data, the utility provides real-time monitoring of the hardware connection itself. Users can view the actual negotiated data speeds, Thunderbolt link throughput, and live voltage readings at each port via a discrete menu bar widget. By exposing what the computer already knows about its peripherals, the app offers a transparent view of hardware performance that standard macOS tools omit.