What the diary reads
The time of your visit, your browser and operating system, your screen size, the page you arrived from, whether you have visited before, how long you stayed and how far you scrolled.
All of it stays in this browser. The diary is stored in local storage on this device. It is never sent to any server. If your browser blocks local storage, the entry exists only for this page load.
Test hooks, used by the operator: ?visit=N previews the Nth visit without touching the diary, ?reset=1 erases it.