WhatCable: Unraveling the USB-C Cable Mystery on macOS

The world of USB-C cables is notoriously complex. What appears to be a simple, identical connector can hide vastly different capabilities—one cable might only charge at 5W, while another supports 100W power delivery, high-speed data, and Thunderbolt 4. This disparity often leads to frustration, as users struggle to identify the right cable for their needs from a drawer full of visually indistinguishable options.

Enter WhatCable, a new open-source macOS menu bar application designed to demystify USB-C cables. Developed in Swift/SwiftUI by sleepingNomad, WhatCable leverages existing macOS system data to inspect connected USB-C cables and present their capabilities in plain English, including charging wattage, data speed, and display support.

Initial Reception and Core Functionality

Upon its release, WhatCable garnered significant attention on Hacker News, with users praising its utility. The app's core promise is to provide clarity where there was once confusion. By reading the e-marker data embedded within compliant USB-C cables, WhatCable can report crucial specifications that are otherwise hidden.

"This is something that I’ve wanted for quite a while. I have lots of mystery USB-C cables that it would be nice to be able to label with their capabilities. Now I can." - dhosek

For many, the app offers a practical solution to a pervasive problem, eliminating the need for external hardware testers or guesswork.

Rapid Development and Community Engagement

One of the most remarkable aspects of WhatCable's launch was the developer's immediate responsiveness to community feedback. Within hours of the Show HN post, sleepingNomad released multiple updates, addressing initial bugs and incorporating feature requests.

"Props to @sleepingNomad here, who has done 16 releases in the last 7 hours, incorporating feedback from HN on the fly! * Don't like menubar apps? you can run it as a normal app * Don't like GUIs? Now you can run it on the command line" - billyhoffman

This rapid iteration saw the introduction of both a standard application mode (for those who prefer not to have another menu bar icon) and a command-line interface (CLI) option, significantly broadening the app's appeal and usability. The CLI option was a direct response to user requests, demonstrating the developer's commitment to user-driven improvements.

Technical Insights and Platform Limitations

WhatCable's ability to read detailed cable information relies on specific IOKit frameworks within macOS, particularly IOPortTransportComponentCCUSBPDSOP. This low-level access to hardware data is crucial for extracting e-marker information, which contains details about the cable's capabilities.

"I'm curious how the SPI to do this (e.g. IOPortTransportComponentCCUSBPDSOP) was discovered. There was nary a mention of it anywhere prior to release." - archagon

This reliance on macOS-specific APIs also explains why the app is currently exclusive to Apple's ecosystem and cannot be distributed via the App Store. Apple's App Sandbox security model restricts the necessary IOKit reads, forcing the app to be distributed outside the official store.

Cross-Platform Potential

The utility of WhatCable sparked discussions about similar solutions for other operating systems. Users inquired about Linux and Windows equivalents, with some pointing to existing projects like lsucpd for Linux, which adds Power Delivery (PD) information to lsusb output. ChromeOS also has built-in USB-C cable identification capabilities, which leverage the same e-marker "Discover Identity" messages that Macs can read.

"Is it also possible to read the e-marker on non-Apple devices? Linux or windows? This would be so useful..." - andix

While the underlying e-marker technology is standard, accessing it programmatically varies significantly across platforms, making direct ports challenging.

User Feedback and Edge Cases

Despite the positive reception, initial users reported a few quirks:

• "No USB-C Ports Detected": Some users, particularly on M1 Pro MacBooks, reported that WhatCable failed to detect connected USB-C devices, even when system information clearly showed them.
• "Plugged in upside down": A peculiar message appeared for some, indicating a Thunderbolt cable was plugged in "upside down," despite USB-C's reversible nature. This suggests a potential misinterpretation of internal port state rather than an actual physical issue.
• Duplicate Devices: In setups with USB hubs or monitors, some users observed the same connected devices appearing under multiple USB ports in WhatCable's interface.

These initial reports highlight the complexities of hardware introspection and the varied nature of USB-C implementations across devices and accessories.

Future Directions and Community Ideas

The community's engagement also brought forth several ideas for future enhancements:

• Homebrew Installation: Many users requested support for Homebrew, a popular package manager for macOS, to simplify installation and updates.
• Cable Quality Leaderboard: One ambitious idea proposed creating an open leaderboard of cable brands and their reported capabilities versus actual performance, potentially leveraging community contributions.
• Accessibility: The app was particularly lauded by a visually impaired user who noted its value in identifying cables without needing physical testers, highlighting its potential for broader accessibility.

The ongoing challenge of accurately representing cable capabilities also surfaced, with a user referencing a recent analysis where many Amazon cables misreported their specs. This raises the question of whether WhatCable, by reading advertised data, can truly catch such discrepancies or if it merely reports what the cable's chip claims.

Conclusion

WhatCable represents a significant step forward in simplifying the often-confusing world of USB-C connectivity for macOS users. Its ability to quickly identify cable capabilities, coupled with the developer's commitment to rapid iteration and community feedback, positions it as a valuable tool. While initial challenges and platform-specific limitations exist, the project's open-source nature and enthusiastic community suggest a promising future for unraveling the mysteries of the modern cable drawer.