This free Mac app reveals the truth about your secret USB-C cables

About three years ago, I showed you amazing $8 cable tester which quickly tells you if your USB-C cable is fast, slow, strong, or weak. Sadly, the tool was discontinued, and I haven’t found anything smart or cheap since. But if you have a Mac with Apple Silicon chips, you can download a very interesting test for free.

It’s called WhatCableand it works by reading information your Mac has already collected about connected USB devices, which Apple usually doesn’t pass on to you. Just click the little widget that sits in the menu bar at the top of your Mac, and you can see every USB-C cable and device on your computer.

Here’s how creator Darryl Morley explained it to me:

Every Apple Silicon Mac has a port controller that handles USB Power Delivery negotiations. When you connect the cable with the e-marker, the port manager sends a “Discover Identity” message to the chip in the cable and returns a standard message: vendor ID, speed limit, current limit, power limit, whether it is active or inactive, etc.

macOS writes that response in the IOKit registry. WhatCable reads using Apple’s public APIs. No access, no privacy rights. The information is not hidden, the Apple firmware does the interview and prints the results. It didn’t appear anywhere on the standard macOS devices. WhatCable reads existing content.

E-marker is one resource. WhatCable also reads from the Mac’s hardware, the actual connection speed, the Thunderbolt link speed, and the live and current power on each port. The device associated with the device tells us what it is, who made it, and what it supports. Put all three together, the cable, the device, and the Mac, and WhatCable can tell you not only what they all claim to support, but what is happening in the connection right now, which part is the obstacle if something does not work as expected.

Want to see it in action? I took pictures and tried on my favorite laces this week. It’s not a perfect solution, because cables can lie about their capabilities, but WhatCable definitely helped me find a bad cable on the way.

When I connected the short, lightweight Satechi cable you see above to the two ports on my MacBook Pro, I got this:

I know from experience that this is correct, and it means that it is still a valuable cable. 480Mbps USB 2.0 is very slow, but the cable shows itself that it can charge at 100 watts, about as fast as my Mac can charge.

This is a little more useful than what my $8 tester would provide. It also shows that this cable only offers USB 2.0 speeds and will probably offer 60W or better charging because the label is there. But it can’t read the e-marker data to say that this cable supports 100W power.

Indeed, I get more than 60W when I plug a 140W battery into my Mac:

WhatCable can detect that I’m connected to a 100W charger, too:

Now, let’s try one of the My five favorite USB-C cables anyway – my 10Gbps, 100W Supercalla cable with magnetic entry beads:

It’s amazing: the cable label says it’s 10Gbps and 100W, but the Mac doesn’t do that!

When I connect a fast 10Gbps SSD, I don’t get the speed with this cable:

And it seems that’s because my daily driver cable has expired. Imagine the time you’ll have to take a break from this job!

Now let’s test the latest and greatest cable in my cabinet: the 240W USB4 40Gbps cable.

Again, the e-marker seems to confirm this speed, although the Mac does not connect itself at that level.

When I plug in the drive, WhatCable detects that the Mac has a 10Gbps link:

It’s the same: this 25GB transfer is measured in seconds instead of minutes:

Here’s a cable that arrived at my house the other day charging 100W. I don’t expect more than USB 2.0 480Mbps data; on Amazon, the company just announced the speed of USB 2.0:

But WhatCable says its e-marker advertises 10Gbps USB 3 data…

I’m not afraid: the cable pen wrote that his body can’t get money. Minutes, not seconds, for the same 25GB transfer:

Here, my $8 tester did a better job, immediately realizing that the cable is not compatible with SS (SuperSpeed, aka USB 3).

It offers a 5 amp charging speed, though:

Next, I decided to connect my USB-A to USB-C magnetic cable, which is only capable of 480Mbps USB 2.0 speeds:

Strangely, the Mac insists it’s running at 10Gbps… That seems wrong!

Finally, here’s the old faithful cable that came with the LaCie drive I bought back in 2019, which I’ve always turned to for stability and speed:

It says it’s like a 20Gbps Thunder cable, even though it says 10Gbps at the end. I don’t have one handy, but I’ll have to try it with Thunder to check!

Morley isn’t the first to note that the MacBook could be testing the USB-C cable. USB connection information is a similar paid program that arrived a year ago. But Morley’s version is free, and he tells me it will “always be free,” even though you can pay $9.99 to get it. Pro version which provides a real-time monitor, monitors, and terminal interface.

Now he has created a very simple idea called WhatPort which automatically monitors what all of your Mac’s USB-C ports are doing right now, including power, data, and video.

Morley tells me he can’t build a version of WhatCable for Windows because “there’s a lot of product diversity and the Windows APIs don’t reflect what WhatCable needs,” and he says Android and iOS alike don’t offer enough access.

He said: “If anyone has a solution to the problem, I’d love to hear it.”

But they’re already working on a Linux port, and they’re still working on the Mac version. You can follow along with the updates on its GitHub page.

Photos by Sean Hollister/The Verge