WhatCable-Linux

What can this USB cable actually do?

A KDE Plasma 6 system tray widget and CLI tool that tells you, in plain English, what each USB device plugged into your Linux machine can actually do.

WhatCable-Linux is a Linux port of WhatCable, a macOS menu bar app by Darryl Morley. This port expands the original USB-C focus to cover all USB devices, while preserving the rich USB-C Power Delivery diagnostics from the original.

What it shows

All USB devices

• Device identity: vendor, product name, serial number
• Speed: negotiated link speed (1.5 Mbps to 20 Gbps)
• USB version: 1.1, 2.0, 3.0, 3.1, 3.2
• Power draw: how much power the device is consuming
• Device type: HID, Audio, Mass Storage, Hub, etc.
• Driver: which kernel driver is handling the device
• Topology: hub hierarchy showing what's plugged into what

USB-C ports (additional detail)

• Port roles: data role (host/device), power role (source/sink)
• Cable e-marker info: cable speed capability, current rating (3A/5A), active vs passive, cable vendor
• Charger PDO list: every voltage/current profile the charger advertises, with the active profile highlighted
• Charging diagnostics: identifies bottlenecks — cable limiting speed, charger undersized, etc.
• Partner identity: decoded from PD Discover Identity VDOs

Install

Build from source

# Install dependencies (Fedora)
sudo dnf install cmake extra-cmake-modules qt6-qtbase-devel qt6-qtdeclarative-devel \
    kf6-kirigami-devel kf6-ki18n-devel kf6-kcoreaddons-devel kf6-kpackage-devel \
    libplasma-devel plasma-workspace-devel systemd-devel

# Install dependencies (Arch/Manjaro)
sudo pacman -S cmake extra-cmake-modules qt6-base qt6-declarative \
    kirigami ki18n plasma-workspace systemd-libs kpackage

# Build
cmake -B build -DCMAKE_INSTALL_PREFIX=/usr
cmake --build build
sudo cmake --install build

# Or install just the plasmoid for your user
kpackagetool6 -t Plasma/Applet -i build/pkg/org.kde.whatcable

CLI only

After building, the whatcable-linux binary is in build/src/cli/:

whatcable-linux              # human-readable summary of every USB device
whatcable-linux --json       # structured JSON output
whatcable-linux --watch      # stream updates as devices come and go
whatcable-linux --raw        # include raw sysfs attributes
whatcable-linux --version
whatcable-linux --help

How it works

WhatCable-Linux reads three areas of the Linux sysfs virtual filesystem. No root access required for basic info:

Hotplug monitoring uses libudev to detect connect/disconnect events in real time.

Cable speed and power decoding follow the USB Power Delivery 3.x spec, ported from the original WhatCable's Swift implementation.

Caveats

• USB-C/PD data availability varies by hardware. The Type-C connector class and USB PD sysfs interfaces depend on the kernel driver (UCSI, TCPM, platform-specific). Some systems expose full PD negotiation data; others expose only basic port info or nothing at all.
• Cable e-marker info only appears for cables that carry one. Same as the original — most USB-C cables under 60W are unmarked.
• WhatCable trusts the e-marker. Counterfeit or mis-flashed cables can lie about their capabilities.
• Vendor name lookup is not exhaustive. Common vendors are recognized; others show the hex VID.

Credits

WhatCable-Linux is a port of WhatCable by Darryl Morley. The USB Power Delivery decoding logic, charging diagnostics, vendor database, and plain-English summary approach are derived from the original macOS app.

License

MIT