Display Diagnostics

The weakest-link idea now has all three legs. WhatCable already told you why a Mac charges slowly (power) and why a drive or dock runs slow (data). This release adds the third: why a monitor isn't running at its full resolution or refresh, and what's holding it back.

What's new

• Display Diagnostics. Plug a monitor in over USB-C or Thunderbolt and WhatCable works out whether the link is actually carrying the monitor's top mode, or falling short. Every port shows a one-line display verdict. Pro adds a dedicated Display Diagnostics screen with the full breakdown: the monitor's native and maximum modes, what the link is carrying, lanes in use versus available, and the link rate.
• It names the adapter. If your monitor is on a USB-C to HDMI or DisplayPort adapter, the verdict says what the adapter reports itself as, for example "a DisplayPort 1.2 adapter using 2 of 4 lanes", so a monitor stuck at 60Hz finally has an explanation you can act on.
• Honest about what it can and can't say. A link below the monitor's top mode can be a cable or adapter limit, or simply the mode you have selected, and passive data can't always tell those apart. So the verdict points at the likely cause without crying wolf, and only says "not the cable" when the evidence actually shows it (a Thunderbolt tunnel, or every lane already in use).

Privacy

• The optional "Contribute Diagnostic Data" feature now also gathers the model and capabilities of any connected display, read from its EDID, with the monitor's serial number removed before anything is sent. The privacy policy now documents the whole Test Kit feature: what it sends, the one-way hashing, and that it is opt-in.

Under the hood

• Display capability is read from the monitor's EDID, including the CTA-861 extension block, so a top mode declared only there is no longer missed.
• A new DisplayPort probe in the Test Kit gathers real-world link and EDID samples to sharpen detection on hardware we don't have to hand.

Install

brew upgrade --cask whatcable, download from Releases, or update in the app.