NimbleCal is built around end-to-end encryption.
What this means
End-to-end encryption means calendar content you save in the app is encrypted on your devices before storage or sync. The keys needed to decrypt that encrypted calendar content do not leave your devices in plaintext, so NimbleCal cannot read it.
Invites are different
Email invites are a separate delivery flow outside the end-to-end encrypted calendar storage path. NimbleCal stores and sends recipient email addresses for delivery, plus the invitation details recipients and email systems need to understand the invite, including the event title, start/end time, timezone, organizer name/email, optional organizer message, and any event location or description.
Email invite details are accessible to anyone with the invite link. Keep invite links private.
See: Invite participants
What might not be encrypted
Some limited metadata may be stored unencrypted so the app can sync records, maintain reminder timing, and support invitation delivery where readable details are needed.
For the detailed, canonical explanation, see: