Nearly three years ago, I showed you an awesome $8 cable tester that quickly tells you if your USB-C cable is likely fast, slow, powerful, or weak. Sadly, that gadget got discontinued, and I’ve never found anything as intuitive or inexpensive since. But if you’ve got a Mac with Apple Silicon chips, you can simply download an even more impressive tester for free.
This free Mac app reveals the truth about your mystery USB-C cables
WhatCable is an excellent free tool.
WhatCable is an excellent free tool.
is a senior editor and founding member of The Verge who covers gadgets, games, and toys. He spent 15 years editing the likes of CNET, Gizmodo, and Engadget.
It’s called WhatCable, and it works by reading the data your Mac already collects about attached USB devices, data that Apple doesn’t normally pass along to you. Just click a little widget that lives in the menu bar atop your Mac, and you can see every USB-C cable and device attached to your computer.
Here’s how creator Darryl Morley explained it to me:
Every Apple Silicon Mac has a port controller chip that handles USB Power Delivery negotiation. When you plug in a cable with an e-marker, the port controller sends a “Discover Identity” message to the chip in the cable and gets back a structured message: vendor ID, speed rating, current rating, voltage limits, whether it’s active or passive, and so on.
macOS writes that response into the IOKit registry. WhatCable reads it using Apple’s public APIs. No root access, no private entitlements. The data isn’t hidden, Apple’s firmware does the negotiation and publishes the result. It’s just not surfaced anywhere in standard macOS tooling. WhatCable reads what’s already there.
The e-marker is one source. WhatCable also reads from the Mac’s own hardware, the actual negotiated connection speed, Thunderbolt link speed, and live voltage and current at each port.
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