// the find
darrylmorley/whatcable
macOS menu bar app that tells you, in plain English, what each USB-C cable plugged into your Mac can actually do
WhatCable is a macOS menu bar app that reads USB-C port state directly from IOKit and tells you what a connected cable can actually do — speed, power rating, e-marker contents, and where the bottleneck is. It's aimed at anyone who's ever wondered why their Mac is charging at 30W when they have a 96W charger, or why an external SSD is slower than expected.
The IOKit integration is genuinely thorough: it reads four distinct service families to pull per-port state, PD identity VDOs from all three SOP message types (cable near-end, far-end, and device), and USB device trees paired to physical ports. The charging diagnostic is specific and actionable — it names the actual bottleneck rather than just reporting the negotiated wattage. The test suite is unusually deep for a utility app: corpus sweep tests, probe sweep tests, reference scenarios from real hardware, and coverage tests for the cable trust logic. The CLI being a first-class target that shares the same diagnostic engine as the GUI (not a thin wrapper) means it's actually usable in scripts and SSH sessions.
Apple Silicon only — Intel Macs can't use it at all because the relevant IOKit accessors don't exist on Titan Ridge controllers, which cuts out every pre-M1 Mac. The cable trust signals are self-described as informational and hedged, which is honest, but in practice they can't tell you whether a cable is dangerous, only that it looks unusual — the real-world value depends heavily on how much you trust the e-marker chip in the first place. The Pro paywall sits behind a one-time purchase but the features split is a bit arbitrary: port health counters and cable resistance estimation feel like things that belong in the free diagnostic, not locked features. Front USB-C ports on Apple Silicon desktops expose no PD data, so Mac mini and Mac Studio users get a degraded experience on ports they likely use daily.