Proton Calendar is built so that nothing outside Proton can sign in to it. That includes calendar tools. It has no CalDAV connection, so Keeper.sh cannot log in to your Proton account the way it does for iCloud or Fastmail.
What Proton does offer is a share link. Keeper.sh reads a calendar link, so your Proton events can show up on Google Calendar or Outlook as busy time.
What does this do, and what does it not?
Proton events are copied onto a Google or Outlook calendar. That is the whole of it.
It only works one way. A calendar read from a link is read-only, so Keeper.sh can send Proton's events out but never write into Proton. Events you add in Google or Outlook will not appear in Proton Calendar.
If you need two-way sync with Proton, Keeper.sh does not do it.
How do you get the link from Proton?
In Proton's steps, open the calendar's settings, go to Calendars, pick the calendar and click Create link under Share with anyone. Then choose how much it shows:
- Limited view shows only busy and free.
- Full view shows titles, descriptions, participants and locations to anyone holding the link.
For avoiding double-booking, choose Limited view. Keeper.sh only needs the time, and a leaked link then shows no detail. What the copy shows is a separate setting, covered in what a copied event shows.
How do you add it to Keeper.sh?
Open Import Calendars and paste the link as a calendar link. Add your Google or Outlook account from the same screen.
Then open the Proton calendar in Keeper.sh and tick the Google or Outlook calendar under Send Events to Calendars.
How quickly do changes arrive?
Slowly, and the delay starts at Proton. Proton says updates may take up to eight hours to appear for anyone reading the link. Keeper.sh copies what the link shows, so the copy is never ahead of that.
That makes this setup good for blocking time you know about in advance, and poor for last-minute changes.
Why isn't it working?
The calendar stops updating. Proton warns that apps reading a link may stop fetching updates, and that you may need to regenerate the link. Create a new link in Proton and replace the old one.
Nothing from Google appears in Proton. A link is read-only, so this direction is not possible.
What does the free plan cover?
Two linked accounts and three connections. A pasted calendar link counts as one account and Google or Outlook is the second, so this uses the whole allowance with one connection.
Where to go next
- Linked accounts and calendars, for how a link differs from a signed-in account
- Sync Google Calendar with Outlook
- Best open-source calendar sync tools