WhatCable, a free macOS application, allows users to identify the capabilities of USB-C cables by reading data from the Mac’s port controller.
How WhatCable Extracts Hidden Hardware Data
USB-C cables often appear identical despite carrying vastly different internal specifications for power, video, and data. The WhatCable app fills this gap by reading information that the operating system already collects but does not surface in standard system tools.
The app leverages Apple’s public APIs to pull data from the IOKit registry. When a cable is plugged in, the Mac’s port controller chip initiates a Discover Identity
handshake with the chip embedded inside the cable. This exchange provides the vendor ID, voltage limits, and speed ratings.
Identifying Bottlenecks in Charging and Data
One of the primary benefits of the software is its ability to pinpoint which component—the cable, the charger, or the Mac port—is limiting performance. The interface provides plain-English updates on connection status, such as Plugged in – 100W charger
or Slow USB device or charge-only cable.
During testing, the software successfully identified cables that were failing despite their specifications. In one instance, a cable that should have supported high-speed transfers repeatedly dropped the connection, leading to a Connection dropped 3 times
notification. In another case, a cable advertised as high-speed was revealed to be a standard USB 2.0 device, with the app showing that the cable’s e-marker wrote checks its body couldn’t cash.
Pro Version Features and Certification Warnings
While the standard version of WhatCable is free, creator Darryl Morley offers a Pro version for users requiring deeper diagnostic insights. This premium tier is available for a one-off fee of £9.99 (approximately $13.40). The Pro version provides a detailed breakdown of the live negotiation process, explaining exactly how and why a connection settled on specific power profiles or transmission speeds.
Users should be aware that the app also checks for USB-IF certification. Additionally, testers have observed that even with software diagnostics, the results are not perfect
because some cables may misreport their own capabilities via their internal chips.
| Feature | WhatCable Capability |
|---|---|
| Data Speed | Decodes link speed and USB 3.2 Gen 2 (10 Gbps) status |
| Power Delivery | Shows negotiated power profile (e.g., 100W) |
| Certification | Identifies vendor and USB-IF status |
| Pro Version | Live negotiation breakdown for £9.99 ($13.40) |
Limitations of Cable Diagnostics
While the app is a powerful tool for Mac users, it remains reliant on the accuracy of the information provided by the cable’s e-marker. The app serves as a diagnostic aid to verify what the hardware claims to be, rather than an absolute guarantee of quality.
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