Apple Silicon Mac users can now identify the true capabilities of their USB-C cables for free using a utility called WhatCable. Created by developer Darryl Morley, the software leverages public macOS APIs to read data from the port controller chip, which negotiates power and data speeds when a cable is connected. According to Morley, the app surfaces technical specifications—such as vendor ID, wattage limits, and data transfer speeds—that are otherwise hidden from the standard macOS interface.
How WhatCable Accesses Hidden Cable Data
Every Apple Silicon Mac features a port controller chip designed to handle USB Power Delivery negotiations. When a cable with an e-marker is plugged in, this chip sends a “Discover Identity” message to the cable. The cable responds with structured data, including its speed rating, current capacity, and voltage limits. macOS stores this information in the IOKit registry, but it does not display it in standard system tools.
WhatCable reads this registry data directly. Because it uses Apple’s public APIs, the app does not require root access or private entitlements. As Darryl Morley notes, the data isn’t hidden by design; it is simply not surfaced in the operating system’s user-facing menus. This allows users to verify if a cable is truly capable of 100W charging or 10Gbps data transfer, even if the cable’s physical labeling is misleading.
Pro Tip: Don’t rely solely on the cable’s exterior markings. Many third-party cables advertise high speeds or power ratings that their internal e-markers—or lack thereof—do not support. Always verify with software if you are experiencing slow data transfers or sluggish charging.
Comparing Software Testers to Hardware Solutions
Before the rise of software-based testing, users often relied on inexpensive hardware dongles. While these $8 gadgets were effective at identifying basic power delivery, they often lacked the ability to read the full e-marker data available through a Mac’s internal controller. For example, a hardware tester might confirm a cable supports 100W charging but fail to report the specific data transfer protocol.
Software solutions like WhatCable provide a more comprehensive view. In testing, the app successfully identified that certain cables—like a short Satechi model—were rated for 5A at 20V (100W). However, it also revealed that other cables, marketed for high speeds, were actually performing at lower USB 2.0 rates, proving that some cables “write checks their bodies can’t cash.”
The Future of USB-C Diagnostics
While the Mac ecosystem now has a reliable, free tool for cable verification, the landscape for other platforms remains fragmented. Darryl Morley states that a Windows version of WhatCable is currently unfeasible due to significant hardware variance and a lack of exposed APIs that provide the same level of low-level access found in Apple’s firmware. Android and iOS platforms face similar limitations regarding internal hardware access.
Despite these hurdles, development continues. Morley has released a companion tool called WhatPort, which monitors the real-time status of each USB-C port, including active power, data, and video throughput. He is also currently working on a Linux port, with updates posted to his GitHub page. For Mac users, a Pro version of WhatCable is available for £9.99, offering a real-time power monitor and terminal diagnostics.
Did you know? Some cables that claim to be 10Gbps are actually limited to 480Mbps USB 2.0 speeds. Using a software diagnostic tool can help you identify these “dud” cables before you waste time waiting for large file transfers to complete.
Frequently Asked Questions
- Is WhatCable free to use? Yes, the core functionality of WhatCable is free, as developer Darryl Morley intends for it to remain accessible. A paid Pro version is available for advanced features.
- Can I use WhatCable on an Intel-based Mac? The software is specifically designed for Apple Silicon Macs, which utilize the proprietary port controller architecture required to read e-marker data.
- Why does my cable report different speeds than advertised? Cables can be mislabeled, or they may simply be wearing out. WhatCable reads the data the cable reports about itself, which can help you identify if a cable is failing or was never designed for high-speed data.
- Will there be a version for Windows or Android? Currently, there are no plans for Windows or Android versions due to hardware and software API limitations that do not provide the necessary low-level access.
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