Select, tap, listen
Select text anywhere on your Mac, tap the right Option key on its own, and Chippy reads it back with the word it is speaking lit.
Chippy is a small app in your Mac's menu bar. Select text in any app, tap the right Option key, and a voice reads it back with the word it is speaking lit.
Install it
Open the download, drag Chippy to Applications, and open it from there. Chippy appears in the menu bar, and in the Dock until you untick Show in Dock in its menu. The first run is a walk of six cards, one of which is your own first read.
The one permission
To read something you selected in another app, macOS has to trust Chippy. The permission is called Accessibility, and it is the only one Chippy asks for. Press Continue on the permission card and allow Chippy when macOS asks. If macOS does not ask, the other button on that card opens the Accessibility row of System Settings, where you switch Chippy on by hand. Turn it off again later and the walk comes back at that card and tells you.
The key, exactly
Nothing about the key is guessable, and everything else depends on it.
It is the Option key to the right of the space bar, tapped on its own and let go. The left Option key does nothing for Chippy. The tap is counted when you release the key, and only if you pressed nothing else while it was down. So holding Option and pressing another key is that shortcut, exactly as it was before you installed Chippy: nothing you already type with Option changes, and no accent starts a read by accident.
When you tap, Chippy asks the app in front for your selection the same way Command C does, so it works anywhere you can copy.
What happens
The panel opens at the bottom right of the screen with your text in it, and the word being spoken is lit as the voice moves through it. Tap again on a different selection and the panel stays where it is and reads the new text.
Tap with nothing selected and the panel says there is nothing to speak, quietly, and makes no sound.
The space bar pauses and plays. The panel's header has Settings, History, Feedback and Close, and Stop is in Chippy's menu in the menu bar.