WhatCable Turns Your Apple Silicon Mac Into a Free USB-C Cable Tester

It's been nearly three years since the $8 USB-C cable tester that everyone loved was discontinued. Since then, finding a replacement that's both cheap and easy has been a chore—unless you own an Apple Silicon Mac. In that case, there's now a free app called WhatCable that may be even better.

WhatCable is a menu-bar utility that reads the data your Mac already collects about connected USB-C cables and devices—data that Apple normally keeps hidden. By tapping into the IOKit registry via public APIs, it shows you the e-marker chip's advertised capabilities (speed, wattage, voltage, active or passive), the actual negotiated connection speed, and live power delivery stats. No root access or private entitlements needed.

This is more than a hardware hunter's toy. While a simple tester reveals whether a cable has an e-marker, WhatCable reads the actual digital claims—and compares them to real-world performance. In practice, that can spot lying cables or worn-out ones. When testing a supposedly 10Gbps 100W cable, WhatCable showed that the e-marker claimed those specs—but the Mac's connection was stuck at USB 2.0. A quick speed test confirmed the cable was failing. It also caught a cable whose e-marker advertised 10Gbps but delivered only USB 2.0 speed, while still charging at 5 amps.

WhatCable is free to use, with a £9.99 Pro version that adds real-time power monitoring, diagnostics, and a terminal view. The developer, Darryl Morley, plans to keep the core free. He's also working on a Linux port (Windows and mobile aren't possible due to API limitations) and has released a simpler companion app called WhatPort that shows live status per port.

If you're a developer or power user juggling multiple USB-C cables, this tool replaces guesswork with hard data. It won't replace a proper multimeter for electrical testing, but for quick validation of cable claims—and catching the ones that are secretly bottlenecking your workflow—it's a no-brainer download.