What Cable is a Bitmoor macOS menu bar app for USB-C diagnostics on Apple Silicon Macs running macOS 14+. It reads the port, cable, charger, adapter, and connected device together, showing speed, power capability, display path, and the weak link using macOS data, not packaging claims. Open source, free, 19 languages, signed and notarized.

Features include charging bottlenecks, mid-session fault warnings, data-speed and display bottlenecks, cable e-marker decoding, active transports (USB 2/3/USB4/Thunderbolt/DisplayPort), engineer mode for raw IOKit properties, and connected device hierarchy. CLI bundled for terminal use with JSON output and watch mode. 125 cable observations in a public database, searchable by vendor, speed, and identity.

Pro version (£9.99 one-time, up to 2 Macs) adds 16 features: cable history with named timelines, live power metering (watts/amps/voltage every 2 seconds), negotiation diagnostics, display diagnostics, port health counters, PD contract inspection, and raw VDO identity. No subscription, no ads, no tracking. Only network calls: version check (free) and license activation (Pro). Diagnostic data never leaves the Mac unless the user contributes.

Works only on Apple Silicon (M1+); Intel Macs lack the port-controller layer What Cable reads. Trust signals flag unusual e-marker data (vendor ID 0x0000, reserved values, mismatched current/speed). Settings: notifications, dock mode, launch at login, hide empty ports.