Sometimes, the littlest things make the biggest differences.

Take, for example, a tiny app released on May 1 that does one thing, does it well, and solves a big problem. WhatCable, created by a U.K. developer, untangles a big mess surrounding USB-C cables.  

These cables have the same connectors, but they can have different capabilities. Some can only charge devices; others can do that and send data; still others can transmit video. There’s an official labeling system that’s supposed to provide the info you need, but cable makers haven’t embraced it.

If you have WhatCable installed on a Mac, plugging a cable into one of the computer’s USB-C ports will show you what it can and cannot do. It doesn’t track you, is open-source and, remarkably, costs nothing. A Windows version is “an aspiration,” its developer says.

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It’s one of those revelatory apps that make you wonder, “Why hasn’t anyone else done this before?” Indeed, I’ve not been able to find any app quite like it for the Mac, and definitely not for Windows. As a result, online reaction has been nearly euphoric among those with a drawer full of unlabeled cables.

As I wrote way back in May 2022, USB-C’s 2014 debut came with a promise to deliver one cable to rule them all. With a single type of USB connector, you’d be able to charge devices, transfer data and even send video — in some cases all of this at the same time — with just one cable.

Indeed, you can now do this. I’m writing this column using a MacBook Pro that’s connected to a 32-inch Dell monitor which includes a built-in connectivity hub. I have just one USB-C cable connecting the laptop to the monitor. The Mac gets its power from the monitor’s hub, and sends video to the display, all using the same cable. Also plugged into the monitor via USB-C is a set of Creative Labs Pebble X Plus speakers, to which the Mac sends audio data over the single cable. It’s magical!

But under my desk is a drawer full of USB cables, with more in my backpack and smaller gear bag. Can all of them pull off this one-cable feat? No. Which ones can? I have no idea!

It’s not like there isn’t a solution here. In 2021, the USB Implementor’s Forum — which helps manage compliance with the USB standard — released a series of logos to make it clear what each cable can do. I have one or two cables at most that feature this labeling. The rest are annoyingly blank. Chances are good your stash of USB-C cables is the same way.

Before WhatCable, the best way to check a cable’s capabilities was through hardware, small modules that provide details about what different kinds of cables can do. Search Amazon for “USB cable tester” and you see dozens of offerings, ranging in price from less than $20 to well over $100. Some are rudimentary, while others have fancy displays and even associated phone apps. But none is as simple and clear as WhatCable, and of course, none is free.

 Darryl Morley, a software developer working in e-commerce in the United Kingdom, says on his GitHub page (a Microsoft-owned site that lets developers to collaborate and share code) that he wrote it to answer the question: “Is this cable any good?” Morley has been working furiously on the app during his off-hours since its May 1 launch and at this writing there have been more than 35 updates. By the time you read this, that number will likely be much bigger.

And because its code is open source, anyone can grab it and improve on it or adapt it for different operating systems. There are already versions for different Linux distributions — on the Hacker News forum thread where he announced its birth, you can see other developers saying they’ve ported it over to different Linux flavors.

Morley said on that thread he would like to do a Windows version, which would have a big audience. But he told me via email that it’s currently not a priority.

“I did mention it in the HN thread but I want to be honest, it’s an aspiration rather than an active project right now,” he said, adding that a Windows release “would essentially be a rebuild from scratch.”

He considers WhatCable a collaboration between himself, the Hacker News community — which has contributed bugs and feature ideas — and AI-based coding tools from OpenAI and Anthropic. That’s why he has been able to update and improve on it so quickly.

“I used both tools deliberately, Claude to write and iterate on the code, Codex to cross check the work. Having two AI models that can disagree with each other turns out to be a useful quality check,” Morley said. “Users found bugs, the AIs fixed them. Sixteen releases in 7 hours was genuinely a conversation between me and AI tools, with HN users as the (quality-control) team.”

When you install WhatCable from whatcable.uk, a tiny USB cable icon appears in the Mac’s Menu Bar. Click it, and if you have any cables plugged into the USB ports on your Mac, you’ll get useful details about what they can do. It also reads the properties of Thunderbolt cables — which share the same kind of connector as USB-C — and MagSafe cables that connect to the magnetic charging port on MacBook Airs and Pros. (You can turn off the Menu Bar icon and just run WhatCable as a standard Dock app.)

For example, the app shows how much power is flowing through a charging cable, as well as the total power it can handle. It will say if a cable can transmit data and how fast, and if it supports video. For example, it shows the cable connecting my MacBook Pro to my Dell monitor is “Charging well at 90W”, and that the charging part of its hub is “well-matched” to the laptop.

The cable also is transmitting at data at “5 Gbps or faster” but is capable of double that. It also shows me the devices connected to the monitor’s hub, including my speakers. You’ll get the most information if the cable has an e-Marker chip that advertises its capabilities. The app also has a “technical details” toggle for even geekier metrics.

I went through my cable collection (you will need to have another device plugged into the other end of each cable; I just used my iPhone) and tested each one. Most of them can send data at USB 2.0 speeds, or 480 Mbps. Only a few could handle super-high-speed data, and only one other could do video.

Be aware that WhatCable only works with Apple Silicon Macs; older, Intel-based Macs aren’t supported. And for now, it doesn’t work with the MacBook Neo, which uses a processor originally designed for the iPhone.

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