Shipping PointerSense: building a tool that disappears into the Mac

PointerSense is live. The idea is simple: hover over any text on your Mac and get an AI explanation near your cursor — no copy-paste, no app-switching, no new window. The implementation is not simple at all.

The constraint that shaped every design decision was invisibility. A menu bar app that announces itself, fires on every cursor movement, or adds visual noise is worse than nothing. The product had to feel like the computer can explain itself, not like another app you manage.

macOS Accessibility APIs are the lever here. Tauri gives you Rust for the native shell and direct access to AXUIElement — cursor position, focused app, hovered or selected text. The integration is fragile: every app exposes different attributes through the Accessibility tree, and some expose nothing useful at all. Detection quality is a feature surface you can never fully control.

The dwell timer is where product intuition matters more than engineering. Too short and it fires on every scroll. Too long and the delay kills the feeling of instant understanding. The right number is not a technical constant — it is a judgment call you can only tune by using the app for a week and watching where it misfires.

Keychain storage for API keys, no explanation history saved by default, app exclusion lists — each of those is a trust feature. They cost one sentence to explain to a user and months to earn back if you get them wrong.