{"id":3644,"date":"2026-07-13T10:13:07","date_gmt":"2026-07-13T10:13:07","guid":{"rendered":"https:\/\/silvybrand.com\/?p=3644"},"modified":"2026-07-13T10:13:07","modified_gmt":"2026-07-13T10:13:07","slug":"whatcable-usb-c-cable-tester-app-mac","status":"publish","type":"post","link":"https:\/\/silvybrand.com\/?p=3644","title":{"rendered":"This free Mac app reveals the truth about your mystery USB-C cables"},"content":{"rendered":"


\n<\/p>\n

\n
\n

Nearly three years ago, I showed you an awesome $8 cable tester<\/a> that quickly tells you if your USB-C cable is likely fast, slow, powerful, or weak. Sadly, that gadget got discontinued, and I\u2019ve never found anything as intuitive or inexpensive since. But if you\u2019ve got a Mac with Apple Silicon chips, you can simply download an even more impressive tester for free.<\/p>\n<\/div>\n

\n

It\u2019s called WhatCable<\/a>, and it works by reading the data your Mac already collects about attached USB devices, data that Apple doesn\u2019t normally pass along to you. Just click a little widget that lives in the menu bar atop your Mac, and you can see every USB-C cable and device attached to your computer.<\/p>\n<\/div>\n

\n

Here\u2019s how creator Darryl Morley explained it to me:<\/p>\n<\/div>\n

\n
\n

Every Apple Silicon Mac has a port controller chip that handles USB Power Delivery negotiation. When you plug in a cable with an e-marker, the port controller sends a \u201cDiscover Identity\u201d message to the chip in the cable and gets back a structured message: vendor ID, speed rating, current rating, voltage limits, whether it\u2019s active or passive, and so on.<\/p>\n

macOS writes that response into the IOKit registry. WhatCable reads it using Apple\u2019s public APIs. No root access, no private entitlements. The data isn\u2019t hidden, Apple\u2019s firmware does the negotiation and publishes the result. It\u2019s just not surfaced anywhere in standard macOS tooling. WhatCable reads what\u2019s already there.<\/p>\n

The e-marker is one source. WhatCable also reads from the Mac\u2019s own hardware, the actual negotiated connection speed, Thunderbolt link speed, and live voltage and current at each port. The connected device tells us what it is, who made it, and what it supports. Put all three together, cable, device, and Mac, and WhatCable can tell you not just what everything claims to support, but what\u2019s actually happening on the connection right now, and which part is the bottleneck if something isn\u2019t performing as expected.<\/p>\n<\/blockquote>\n<\/div>\n

\n

Want to see it in action? I took photos while testing some of my favorite cables this week. It\u2019s not a perfect solution, as cables can lie about their capabilities, but WhatCable genuinely helped me find a bad cable along the way.<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

When I plugged in the short, lightweight Satechi cable you see above into two ports on my MacBook Pro, I got this:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"The<\/a><\/div>\n<\/div>\n<\/div>\n

The important part here is \u201cCable rated for 5 A at up to 20V (~100W)\u201d. It\u2019s a good charge cable.<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

I know from experience that this info is correct, and that means it\u2019s still a valuable cable. 480Mbps USB 2.0 is very slow, but the cable is self-reporting it can charge at 100 watts, nearly as fast as my Mac can charge.<\/p>\n<\/div>\n

\n

That\u2019s slightly more useful info than my $8 tester can provide. It, too, shows that the cable only offers USB 2.0 speeds and probably offers 60W or better charging because an e-marker exists. But it can\u2019t read e-marker data to tell that this cable supports 100W charging speeds.<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Sure enough, I\u2019m getting more than 60W when I plug a 140W battery into my Mac:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

WhatCable can detect that I\u2019m connected to a 100W charger, too:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201cPlugged<\/a><\/div>\n<\/div>\n<\/div>\n

\u201cPlugged in – 100W charger.\u201d<\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

Now, let\u2019s try one of my five favorite USB-C cables<\/a> yet \u2014 my 10Gbps, 100W Supercalla cable with magnetic winding beads:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"My<\/a><\/div>\n<\/div>\n<\/div>\n

My Supercalla cable.<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

That\u2019s strange: the cable\u2019s e-marker does claim it\u2019s 10Gbps and 100W, but the Mac isn\u2019t treating it that way!<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201cSlow<\/a><\/div>\n<\/div>\n<\/div>\n

\u201cSlow USB device or charge-only cable.\u201d<\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

When I plug in a fast 10Gbps SSD, I\u2019m not getting that speed with this cord:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

And it appears that\u2019s because my daily driver cable is finally wearing out. Guess it\u2019s time to retire this one!<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201cConnection<\/a><\/div>\n<\/div>\n<\/div>\n

\u201cConnection dropped 3 times.\u201d<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

Now let\u2019s try the theoretically latest and greatest cable in my drawer: a 240W USB4 40Gbps cable.<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Again, the e-marker seems to validate those speeds, even if the Mac isn\u2019t connecting to itself at that rate.<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201c40<\/a><\/div>\n<\/div>\n<\/div>\n

\u201c40 Gbps, Thunderbolt 4 class.\u201d<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

Once I plug in the drive, WhatCable detects that the Mac has a 10Gbps link:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201cDevice<\/a><\/div>\n<\/div>\n<\/div>\n

\u201cDevice runs at 10 Gbps.\u201d<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

That\u2019s more like it: this 25GB transfer is measured in seconds instead of minutes:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Here\u2019s a cable that arrived at my home just the other day exclusively for 100W charging. I\u2019m not expecting more than USB 2.0 480Mbps data; on Amazon, the company only advertised USB 2.0 speeds:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

But WhatCable says its own e-marker advertises 10Gbps USB 3 data\u2026 could it be?<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201cCable<\/a><\/div>\n<\/div>\n<\/div>\n

\u201cCable speed: USB 3.2 Gen 2 (10 Gbps).\u201d<\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

I\u2019m afraid not: this cable\u2019s e-marker wrote checks its body couldn\u2019t cash. Minutes, not seconds, for the same 25GB transfer:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Here, my $8 tester did a better job, immediately detecting that the cable doesn\u2019t support SS (SuperSpeed, aka USB 3).<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"Note<\/a><\/div>\n<\/div>\n<\/div>\n

Note that the SS (SuperSpeed) light isn\u2019t lit.<\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

It delivers on the 5 amp charging speeds, though:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\u201c20Gbps<\/a><\/div>\n<\/div>\n<\/div>\n

\u201c20Gbps capable.\u201d But is it really? <\/em><\/figcaption><\/p>\n<\/div>\n<\/div>\n<\/div>\n
\n

Next, I thought I\u2019d plug in my magnetic accordion USB-A to USB-C cable, which is definitely only capable of 480Mbps USB 2.0 speeds:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Strangely, the Mac insists it\u2019s running at 10Gbps\u2026 while connected to my external battery. That seems wrong!<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Last but not least, here\u2019s the old faithful cable that came with a LaCie drive I bought way back in 2019, one I\u2019ve always turned to for stability and speed:<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

It\u2019s reporting as a 20Gbps Thunderbolt cable, even though it says 10Gbps on the end. I don\u2019t have one handy, but I\u2019ll have to try it with a Thunderbolt drive to check!<\/p>\n<\/div>\n

\n
\n
\n
\n
\n
\"\"<\/a><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\n

Morley isn\u2019t the first to realize a MacBook could be a USB-C cable tester. USB Connection Information<\/a> is a similar paid app that arrived a year ago. But Morley\u2019s version is free, and he tells me it \u201cwill always stay free at its core,\u201d though you can pay \u00a39.99 to get the Pro version<\/a> that offers a real-time power monitor, diagnostics, and a terminal view.<\/p>\n<\/div>\n

\n

He\u2019s also now built an even simpler version of the idea called WhatPort<\/a> that simply monitors what each of your Mac\u2019s USB-C ports is doing right now, including power, data, and video.<\/p>\n<\/div>\n

\n

Morley tells me he won\u2019t be able to build a version of WhatCable for Windows because \u201cthere\u2019s too much hardware variance and the Windows APIs don\u2019t expose what WhatCable needs,\u201d and says Android and iOS similarly don\u2019t provide enough low-level access.<\/p>\n<\/div>\n

\n

\u201cIf anyone has a workaround I\u2019d love to hear it,\u201d he says.<\/p>\n<\/div>\n

\n

But he\u2019s already working on a Linux port, and is continuing to update the Mac version. You can follow along with the updates at his GitHub page<\/a>.<\/p>\n<\/div>\n

\n

Photos by Sean Hollister \/ The Verge<\/em><\/p>\n<\/div>\n

Follow topics and authors<\/strong> from this story to see more like this in your personalized homepage feed and to receive email updates.<\/span><\/p>\n