What can this USB-C cable actually do?

Website: whatcable.uk (overview, screenshots, and CLI docs)

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.

Per port, in plain English:

• At-a-glance headline: Thunderbolt / USB4, USB device, Display connected, 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
• Cable trust signals: an orange card appears when the e-marker reports values that look unusual against the USB-PD spec, like a zero vendor ID, a reserved bit pattern in the speed / current / cable-latency fields, or a VID that isn't in USB-IF's published list. Wording is hedged on purpose: a flag means "this looks unusual," not "this cable is fake."
• 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
• Thunderbolt fabric: when a Thunderbolt / USB4 link is active, shows per-lane speed, generation (TB3, TB4, TB5), and the full switch topology for multi-hop connections through docks
• Cable identification: if the cable's e-marker fingerprint matches a known cable in the bundled database, the brand and model are shown alongside the raw specs
• Active transports: USB 2 / USB 3 / Thunderbolt / DisplayPort
• Desktop widget: small, medium, and large WidgetKit widgets showing live cable status on your desktop
• ⌥-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
• Adjust the font size
• Switch language (English, Armenian, Italian, Polish, Simplified Chinese, or follow your system default)
• 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.

WhatCable is free and open source. If you find it useful, you can support the project by picking up WhatCable Pro, which unlocks a ton of extra features: live power metering, PD contract inspection, port health counters, pin diagrams, cable resistance estimation, liquid detection status, and a dedicated power monitor window. One-time purchase, works on up to 2 Macs.

Visit whatcable.uk for an overview and screenshots, or install directly below.

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

The app is signed with a Developer ID and notarised by Apple, so there are no Gatekeeper warnings.

It's not on the Mac App Store on purpose: App Sandbox blocks the low-level IOKit reads WhatCable depends on, so it ships signed and notarised outside the store instead.

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.

brew tap darrylmorley/whatcable
brew install --cask whatcable

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

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

$ whatcable

USB-C Port 1
  ✓ Charging well at 96W
  Cable: 5A, 100W, USB4 40 Gbps
  Charger: 5V / 9V / 15V / 20V PDOs

USB-C Port 2
  ! Cable is limiting charging speed
  Cable: 3A, 60W, USB 2.0
  Device: External SSD, USB 10 Gbps

Flags:

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 --report       # open a pre-filled GitHub issue for the connected cable
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.

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

Cable speed and power decoding follow the USB Power Delivery spec (aligned to USB-PD R3.2 V1.2, March 2026). Vendor names come from a bundled SQLite database (whatcable.db) that merges USB-IF's published vendor list (~13,700 entries), the community usb.ids list, and a curated set of cable fingerprints reported by users.

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

Requires Swift 5.9+ (Xcode 15+).

./scripts/smoke-test.sh

Builds, signs, notarises (if configured), and smoke-tests the app. Produces dist/WhatCable.app and dist/WhatCable.zip. Safe to run on any branch, any time. Does not touch the Homebrew tap.

Modes:

Cutting a release:

# write release-notes/v<version>.md first, then:
./scripts/release.sh <version>

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

• 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.
• Some cables only reveal their e-marker once something is plugged in at the other end. The chip in the cable's plug runs off VCONN (a small power rail your Mac feeds into the cable) and only answers when the host issues a "Discover Identity" message. With nothing attached, some Macs read the e-marker straight away, others wait until they see a real partner to negotiate with. If a cable shows up as basic when bare, plug a charger, dock, or device into the far end and check again.
• WhatCable trusts the e-marker for capabilities. Cable speed, current rating, and vendor come straight from the chip in the cable's plug, and software cannot verify what's inside the jacket. If a cable claims 240W / 40 Gbps but performs poorly, the chip is lying, not WhatCable. The trust-signals card flags a small set of internal-consistency tells (zero VID, reserved bit patterns in the Cable VDO, a VID not in the USB-IF list) that often appear on counterfeit or mis-flashed cables, but those flags are hedged signals, not proof.
• PD spec coverage: the decoder is aligned to USB-PD R3.2 V1.2 (March 2026). Earlier 3.0 / 3.1 cables work fine.
• Vendor name lookup uses a bundled database (~13,700 USB-IF entries plus the community usb.ids list). VIDs assigned after the bundled snapshot will show as "Unregistered / unknown" and trip a trust-signal flag until the database is refreshed.
• 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.

@abrauchli built a Rust port for Linux called usbeehive. Really nice work. Install it with cargo install usbeehive. It started life as a whatcable crate on crates.io before being renamed to avoid confusion with this repo. He's also working on usbee, a GNOME UI for it (early stage, but the basics work).

WhatCable reads USB-C port state directly from IOKit on your Mac. All of that happens locally. Nothing is sent anywhere automatically.

Cable reports: If you use the "Report this cable" button on an e-marked cable, WhatCable builds a pre-filled GitHub issue containing the cable's vendor ID, product ID, and capability flags (VDOs). Your browser opens with that data in the issue form. Nothing is submitted until you click the button in GitHub yourself. Once submitted, the issue is public.

Update checks: WhatCable periodically checks the GitHub Releases API to see if a newer version is available. No personal data or hardware info is included in that request.

Issues and PRs welcome. The code is small and tries to stay readable.

Where to start:

• Sources/WhatCable/ContentView.swift for the UI
• Sources/WhatCableCore/PortSummary.swift for the plain-English diagnostic logic
• Sources/WhatCableCore/PDVDO.swift for USB-PD bit decoding
• Sources/WhatCableDarwinBackend/ for the IOKit watchers (port state, PD identity, power sources, USB devices, Thunderbolt fabric)
• Sources/WhatCableCLI/ for the CLI, which shares WhatCableCore with the menu bar app

WhatCable uses .lproj/.strings files for localisation. Each module (WhatCable and WhatCableCore) has its own set under Sources/<module>/Resources/<lang>.lproj/Localizable.strings.

To add a new language:

1. Copy en.lproj/Localizable.strings from both modules into a new <lang>.lproj/ directory
2. Translate the values (leave the keys as-is)
3. Make sure format specifiers (%@, %lld, %1$@, etc.) match the English originals exactly
4. Run plutil -lint on your files to check for syntax errors
5. Add the language to the picker in Sources/WhatCable/SettingsView.swift

If you have a cable with an e-marker, the "Report this cable" button in the app (or whatcable --report from the CLI) opens a pre-filled GitHub issue with the cable's fingerprint. This helps build the bundled cable database so future users see brand/model info for known cables.

Built by Darryl Morley.

Contributors:

• @rolandgroen - option-click technical details, gear menu in popover
• @0x687931 - UI polish, hardware matching, updater hardening, USB-C/MagSafe fix
• @blech - USB device matching for hubs, settings view, Cmd+R refresh shortcut
• @willhsieh - window/Dock mode
• @hobostay - SIGTERM handling, charging threshold fix, installer temp file leak fix
• @JimmFly - localisation infrastructure, Simplified Chinese translation
• @IonBazan - i18n migration to .lproj/.strings, Polish translation, obsolete vendor IDs
• @bovirus - Italian translation
• @Vardan933 - Armenian translation
• @abrauchli - screenshot fix
• @durul - updater security audit
• @nervous-inhuman - USB device matching and port state bug reports
• @hgschmie - e-marker and Thunderbolt cable documentation that led to e-marker detection
• @joeshaw - dual power source bug report, Thunderbolt data samples
• @jlbyrne-76 - M4 Mac Mini front port e-marker bug report, cable reports
• @stevetrease - M3 and M4 ioreg dumps, TB3 data samples
• @jshier - M3 Ultra Thunderbolt data, AppleSmartBattery dumps
• @NoFr1ends - TB5 hardware confirmation (JHL9580 dock, M5 Pro)

Sponsors:

• @1A1zRyan
• @SpartanDavie
• @zippykeyop

Thanks to everyone who has filed cable reports, bug reports, and IOKit dumps. These contributions directly improve the cable database and help WhatCable handle more hardware correctly.

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