What does the WhatCable app do?

It reads each USB-C port on a Mac and displays the maximum data rate of the connection along with the USB Power Delivery profiles it supports. It works on MacBook Pro, MacBook Air, MacBook Neo, Mac mini and iMac. The information comes from the cable's eMarker chip and the port itself, so no extra hardware is needed.

There is a free version that covers the core read-out, plus a Pro version at a one-time price of £9.99, roughly $13. For sorting a drawer of unlabelled cables the free version answers the main questions: whether an eMarker is present, what it declares, and what the current connection is actually running at.

Why did the app report my Thunderbolt cable as USB 2.0?

Because it reports the link, not the cable in isolation. A connection settles at the lowest common capability of host port, cable and peripheral, so a Thunderbolt cable attached to a non-Thunderbolt device really is a USB 2.0 link at that moment. Retest the same cable on a port you know supports Thunderbolt or USB4 to see its own capability.

Can an app tell whether a USB-C cable is lying about its rating?

No. The app reads the eMarker, which is firmware holding declared values, and reports them faithfully. Nothing in a software read-out measures the conductors, the shield or the connector. A mis-programmed chip therefore reads as clean. Confirming a rating physically requires load testing and signal measurement on an instrument, not a host-side query.

Why does the app show no data rate for some cables?

Those cables have no eMarker. Power information still appears, because a cable declaring nothing is limited to 3 A by the specification and the host assumes that default, but there is no chip to report a speed. On a cable sold as 100 W or 240 W this is a red flag: without an eMarker it cannot negotiate above 3 A and a charger will cap it at 60 W.

Does reading the eMarker tell me the cable is safe?

It tells you the cable claims a rating and that a charger will act on that claim. It does not confirm the conductors, crimps or shield can sustain it. Safety at high current depends on conductor gauge, termination quality and heat behaviour under sustained load, none of which a host-side read-out can observe. Treat the read-out as identification, not certification.

2026-07-13

TT作者Tonetron Engineering Team · Dongguan Taitron Electronic Limited

免费应用揭示适用于 MacBook Air 等设备的 USB-C 线缆性能

USB-C 线缆的性能差异显著：数据传输速率从 480 Mbps 到 120 Gbps，供电功率从 5 W 到 240 W。WhatCable 这款免费 macOS 应用可识别每根线缆的具体能力。

USB-C 本应让生活更简单，但无标识的线缆却让这一标准变得不必要地复杂。从 480 Mbit/s 到 120 Gbit/s、从 5 瓦到 240 瓦——USB-C 线缆的性能可能差异显著。WhatCable 是一款免费的 macOS 应用，可显示一条线缆具备哪些能力。

关于作者

Tonetron Engineering Team· Dongguan Taitron Electronic Limited

Tonetron is the export brand of Dongguan Taitron Electronic Limited, a cable and connectivity manufacturer in Dongguan, Guangdong, China. Our engineering and QA teams write these guides from our own production and test experience — including HDMI Forum ATC confirmations (certificates 5QSIMQP4DLG, 2JCHSF3SL1X, MG3CQ3Z4BAG) and USB-IF USB4 certification testing passed under TID 6801. Our USB-IF membership has since lapsed, so that entry is no longer in the public USB-IF product search; the certificate itself is published on our credentials page. The credential you can verify yourself right now: we have been a licensed HDMI Adopter since June 2005 — searchable under “Taitron” in the official HDMI Adopter directory.

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