Share at the narrowest level each app offers and put the coordination fact in the entry title. In Google Calendar that level is "See only free/busy (hide details)", which shows when you are busy without event names or details, and the same page says an administrator can have special permissions to find your calendar and all event details even when you have not shared it (Share your calendar). Outlook's equivalent is "Can view when I'm busy" (Share an Outlook calendar as view-only with others), and iCloud's is Read-Only, which Apple describes as letting the invitee view but not edit the calendar (Share a calendar on iCloud.com).
The narrowest setting in each of the three apps
The three apps do not offer the same ladder, and the middle rung is where they differ. Outlook has a level between busy and everything: "Can view titles and locations" shows when you are busy plus the titles and locations of items, while "Can view all details" shows all details without allowing changes (Share an Outlook calendar as view-only with others).
Google Calendar has no titles-only rung. Its levels run from "See only free/busy (hide details)" straight to "See event details", then through three editing levels up to "Make changes and manage sharing" (Share your calendar). So the choice in Google is binary: the block, or the whole event.
iCloud splits on a different axis. A private share requires the invitee to have an Apple Account and use iCloud, and gives them either Read-Only or Allow editing, which lets them create, edit and delete events and track invitation responses. A public calendar is a link that anybody can view without an account (Share a calendar on iCloud.com).
Scroll sideways to see the full table →
| App | Shows only that you are busy | Shows titles and locations | Shows everything or allows changes |
|---|---|---|---|
| Google Calendar | "See only free/busy (hide details)" | No separate level | "See event details", up to "Make changes and manage sharing" |
| Outlook | "Can view when I'm busy" | "Can view titles and locations" | "Can view all details"; editing is handled through delegation |
| iCloud | No separate level | No separate level | "Read-Only", or "Allow editing" |
Read the row for the app you actually have, on the account you actually have. A personal account and an employer-managed account behave differently, and the difference shows up on the day it matters.
What the setting does not cover
The permission controls one view. It does not control the copy. A screenshot, a forwarded invitation, a notification on a lock screen and a printed week all leave the view you configured, and none of them change back when you tighten the setting.
Fields other than the description carry information too. The location, the name of an attachment and the list of people invited each say something. So does a title, which is why Outlook keeps titles and locations on the same rung (Share an Outlook calendar as view-only with others).
A paper calendar follows the same purpose test. A kitchen wall, a break room and a front desk have three different audiences. Put the block on the wall and keep the reason in a notebook.
Put the coordination fact in the title, not the reason
An entry reading only "Busy" is private and useless. The person reading it still has to ask a question, which is the thing the calendar was supposed to prevent. "Unavailable until noon, Alex has pickup" is the same privacy with the answer included.
Three rules make the titles work: name the hours, name the owner of anything that has to happen, and name the time you will update an uncertain finish. Only put another person's name or number in an entry with their agreement. Explaining availability without the personal details covers the same move in a message rather than a calendar, and the household version is in sharing a calendar across different shifts.
An example: a Thursday morning appointment
Example. A 9:30 am appointment, 25 minutes each way, expected to run 45 minutes, on a day with a 1:00 pm shift. Three audiences get three different things from the same event.
The work calendar gets free/busy only: a block from 9:00 am to noon with no title, under Google's "See only free/busy (hide details)" (Share your calendar). The relative driving gets a message with the address and a pickup time of 9:00 am. The household calendar gets "Sam unavailable 9:00 am to noon, home by 12:30".
Before trusting any of it, make one ordinary test event with no personal detail in it and ask somebody who holds the access to read back the title, the location and the notes. When access ends, remove it through the app's own process rather than deleting events, and tell the person what replaces it.
Write the entry this way: "Unavailable 9:00 am to noon Thursday, home by 12:30, Alex has the 3:15 pickup."