WhatCable — macOS Menu Bar App That Identifies USB-C Cable Capabilities

Introduction

WhatCable is an open-source macOS menu bar app that reads USB-C cable metadata through IOKit and displays, in plain language, what each connected cable supports — data speed, charging wattage, video output, and Thunderbolt compatibility. It solves the universal frustration of not knowing which USB-C cable does what.

What WhatCable Does

• Detects all USB-C cables currently connected to your Mac
• Reports maximum data transfer speed (USB 2.0, 3.x, 4.0, Thunderbolt)
• Shows maximum power delivery wattage the cable supports
• Indicates video output capability (DisplayPort Alt Mode, Thunderbolt)
• Presents all information in a clean, human-readable menu bar popover

Architecture Overview

WhatCable is a native SwiftUI macOS app that queries the IOKit framework to read USB Power Delivery and Billboard BOS descriptors from connected cables. It maps raw USB descriptor fields to human-readable capabilities using Apple's IOUSBHostDevice APIs. The app runs as a lightweight menu bar agent with minimal memory and CPU footprint, polling for cable changes on connect/disconnect events.

Self-Hosting & Configuration

• Install via Homebrew Cask or download from GitHub Releases
• Requires macOS 13 Ventura or later
• No configuration needed — launches as a menu bar icon automatically
• Optionally set to launch at login via System Settings
• Works on both Intel and Apple Silicon Macs

Key Features

• Instant identification of USB-C cable specs without any manual lookup
• Native SwiftUI interface that matches macOS design language
• Zero configuration — plug in a cable and read the result
• Lightweight menu bar agent with negligible resource usage
• Open-source with no telemetry or network access required

Comparison with Similar Tools

• System Information (macOS) — shows USB devices but not cable-specific capabilities; WhatCable focuses on cable specs
• USB Prober — Apple developer tool for raw USB descriptors; WhatCable translates these into plain English
• USBDeview (Windows) — Windows USB device viewer; WhatCable is macOS-native and cable-focused
• Cable labeling — physical labels fade or are absent; WhatCable provides instant digital identification
• Thunderbolt Accessories — macOS settings panel shows Thunderbolt devices but not cable wattage or USB details

FAQ

Q: Does WhatCable work with all USB-C cables? A: It works with cables that expose USB PD and Billboard descriptors. Very cheap cables with no electronic marker chip may show limited information.

Q: Can it detect cable length or brand? A: No, cable length and brand are not stored in USB descriptors. WhatCable reports electrical capabilities only.

Q: Does it work with USB-C to USB-A adapters? A: It detects the adapter as a connected device but cable-specific metadata depends on the adapter's descriptor support.

Q: Is there a Windows or Linux version? A: No, WhatCable is macOS-only, built on Apple's IOKit framework.

Sources

• https://github.com/darrylmorley/whatcable