WhatCable

What can this USB cable actually do?

A command-line tool that tells you, in plain English, what each USB device plugged into your Linux machine can actually do.

WhatCable 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.

This repository is a Rust rewrite forked from Zetaphor/whatcable-linux (originally C++/CMake).

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

Requires Rust 1.74+ (install via rustup) and libudev development headers (used for --watch hotplug support, enabled by default).

# Ubuntu / Debian
sudo apt install libudev-dev pkg-config

# Fedora
sudo dnf install systemd-devel pkgconf-pkg-config

# Arch / Manjaro
sudo pacman -S --needed systemd-libs pkgconf

Build:

cargo build --release                              # default (with --watch)
cargo build --release --no-default-features        # without libudev / --watch
sudo install -Dm755 target/release/whatcable-linux /usr/local/bin/whatcable-linux

Tests

cargo test --no-default-features    # avoids libudev requirement
cargo test                          # full suite, requires libudev-dev

Usage

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

sysfs path	What it gives us
`/sys/bus/usb/devices/`	All USB devices: vendor, product, speed, power, class, interfaces, topology
`/sys/class/typec/`	USB-C port state: connection, roles, cable e-marker, partner identity
`/sys/class/usb_power_delivery/`	PD negotiation: PDO list from charger, active profile, PPS ranges

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

Upstream Linux/KDE codebase: Zetaphor/whatcable-linux.

WhatCable 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

whatcable 0.2.1