GitHub - darrylmorley/whatcable: macOS menu bar app that tells you, in plain English, what each USB-C cable plugged into your Mac can actually do

What can this USB-C cable actually do?

A small macOS menu bar app that tells you, in plain English, what each USB-C cable plugged into your Mac can actually do, and why your Mac might be charging slowly.

USB-C hides a lot under one connector. Anything from a USB 2.0 charge-only cable to a 240W / 40 Gbps Thunderbolt 4 cable, all looking identical in your drawer. macOS already exposes the relevant info via IOKit; WhatCable surfaces it as a friendly menu bar popover.

What it shows

Per port, in plain English:

At-a-glance headline: Thunderbolt / USB4, USB device, Charging only, Slow USB / charge-only cable, Nothing connected
Charging diagnostic: when something's plugged in, a banner identifies the bottleneck:
- "Cable is limiting charging speed" (cable rated below the charger)
- "Charging at 30W (charger can do up to 96W)" (Mac is asking for less, e.g. battery near full)
- "Charging well at 96W" (everything matches)
Cable e-marker info: the cable's actual speed (USB 2.0, 5 / 10 / 20 / 40 / 80 Gbps), current rating (3 A / 5 A up to 60W / 100W / 240W), and the chip's vendor
Charger PDO list: every voltage profile the charger advertises (5V / 9V / 12V / 15V / 20V…) with the currently negotiated profile highlighted in real time
Connected device identity: vendor name and product type, decoded from the PD Discover Identity response
Attached USB devices: storage, hubs, and peripherals listed under the physical port they're plugged into, with their negotiated speed
Active transports: USB 2 / USB 3 / Thunderbolt / DisplayPort
⌥-click the menu bar icon (or flip the toggle in Settings) to reveal the underlying IOKit properties for engineers

Click the gear icon in the popover header to open Settings, where you can:

Hide empty ports
Launch at login
Run as a regular Dock app instead of a menu bar icon
Get notifications when cables are connected or disconnected

Right-click the menu bar icon for Refresh, a Keep window open toggle (handy for screenshots and demos), Check for Updates…, About, WhatCable on GitHub, and Quit.

Install

Download the latest WhatCable.zip from the Releases page, unzip, and drag WhatCable.app to /Applications.

The app is universal (Apple silicon + Intel), signed with a Developer ID, and notarised by Apple, so there are no Gatekeeper warnings.

Requires macOS 14 (Sonoma) or later. Apple Silicon only. On Intel Macs, the USB-C ports are driven by Intel Titan Ridge / JHL9580 Thunderbolt 3 controllers, and the USB-PD state and cable e-marker data WhatCable depends on are not exposed through any public IOKit accessor.

Note: The manual install gives you the menu bar app only. The whatcable CLI is bundled inside the .app and is not on your PATH by default. If you want to use it from the shell, see the Command-line interface section below for the one-line symlink. Or install via Homebrew, which sets up the CLI automatically.

Homebrew

brew tap darrylmorley/whatcable
brew install --cask whatcable

This installs the menu bar app and symlinks the whatcable CLI into your PATH.

Command-line interface

A whatcable binary ships alongside the menu bar app, driven by the same diagnostic engine:

whatcable                # human-readable summary of every port
whatcable --json         # structured JSON, pipe into jq
whatcable --watch        # stream updates as cables come and go (Ctrl+C to exit)
whatcable --raw          # include underlying IOKit properties
whatcable --version
whatcable --help

If you installed the .app manually rather than via Homebrew, the CLI lives at WhatCable.app/Contents/Helpers/whatcable. Symlink it into your PATH if you want it on the shell:

ln -s /Applications/WhatCable.app/Contents/Helpers/whatcable /usr/local/bin/whatcable

The Homebrew install does this for you automatically.

How it works

WhatCable reads four families of IOKit services. No entitlements, no private APIs, no helper daemons:

Service	What it gives us
`AppleHPMInterfaceType10/11/12` (M3-era) and `AppleTCControllerType10/11` (M1 / M2)	Per-port state: connection, transports, plug orientation, e-marker presence. `Type11` is what M2 MacBook Air uses for its MagSafe 3 port.
`IOPortFeaturePowerSource`	Full PDO list from the connected source, with the live "winning" PDO
`IOPortTransportComponentCCUSBPDSOP`	PD Discover Identity VDOs for SOP (port partner) and SOP' (cable e-marker)
XHCI controller subtree	Each connected USB device is paired to its physical port via the XHCI port node's `UsbIOPort` registry path, falling back to a bus-index derived from the controller's `locationID` upper byte and the port's `hpm` SPMI ancestor on machines that don't expose `UsbIOPort`.

Cable speed and power decoding follow the USB Power Delivery 3.x spec.

Build from source

swift run WhatCable          # menu bar app
swift run whatcable-cli      # CLI

Requires Swift 5.9 (Xcode 15+).

Build a distributable .app

Produces a universal dist/WhatCable.app (arm64 + x86_64) and dist/WhatCable.zip.

Modes:

Configuration	Result
No `.env`	Ad-hoc signed. Works locally; Gatekeeper warns on other Macs.
`.env` with `DEVELOPER_ID`	Developer ID signed + hardened runtime.
`.env` with `DEVELOPER_ID` + `NOTARY_PROFILE`	Full notarisation + stapled ticket. Gatekeeper-clean for everyone.

Cutting a release:

# write release-notes/v0.5.3.md first, then:
./scripts/release.sh 0.5.3

The wrapper does the whole pipeline: bumps the version, runs build-app.sh (which builds, signs, notarises, smoke-tests, and bumps the local cask), tags and pushes the commit, creates the GitHub release with the notes file, verifies the uploaded asset's sha matches the local zip, copies the notes into the tap, and pushes the tap. Use --dry-run first to validate state. Requires gh (auth'd) and the env vars from .env.example.

One-time setup for full notarisation:

# 1. Find your signing identity
security find-identity -v -p codesigning

# 2. Store notarytool credentials in the keychain
xcrun notarytool store-credentials "WhatCable-notary" \
    --apple-id "you@example.com" \
    --team-id "ABCDE12345" \
    --password "<app-specific-password>"   # generate at appleid.apple.com

# 3. Create your .env from the template
cp .env.example .env
# ...and fill in DEVELOPER_ID

Caveats

Cable e-marker info only appears for cables that carry one. Most USB-C cables under 60 W are unmarked. Any Thunderbolt / USB4 cable, any 5 A / 100 W+ cable, and most quality data cables will be e-marked.
WhatCable trusts the e-marker. The cable speed, current rating, and vendor are read straight from the chip in the cable's plug. Counterfeit or mis-flashed cables can advertise capabilities they don't actually deliver, and there's no way for software to verify what's inside the jacket. If a cable claims 240W / 40 Gbps but performs poorly, the chip is lying, not WhatCable.
PD spec coverage: the decoder targets PD 3.0 / 3.1. PD 3.2 EPR variants may need tweaks once we see real data.
Vendor name lookup is bundled but not exhaustive: common cable, charger, hub, dock, and storage vendors are recognised; others fall back to the hex VID.
macOS only. iOS sandboxing makes USB-C e-marker access much harder.
Apple Silicon only. Intel Macs route USB-C through Intel Thunderbolt 3 controllers (Titan Ridge / JHL9580). Apple's IOKit driver for those chips does not expose the USB-PD negotiation state or the cable e-marker VDOs, so there's no path to surface the same information on Intel hardware.
Not on the App Store. App Sandbox blocks the IOKit reads we depend on.

Contributing

Issues and PRs welcome. The code is small and tries to stay readable. Start at Sources/WhatCable/ContentView.swift for the UI, Sources/WhatCableCore/PortSummary.swift for the plain-English logic, or Sources/WhatCableCore/PDVDO.swift for the bit-twiddling. The diagnostic engine lives in WhatCableCore, which is shared by the menu bar app and the whatcable CLI in Sources/WhatCableCLI/.

Credits

Built by Darryl Morley.

Inspired by every time someone has asked "is this cable any good?".