Select the “Mail Plus” or “Proton Unlimited” paid plans for more features.
Reviewed by Gabriel Bachmann
Proton Calendar
proton.me/calendar 2 ratings so far*
Rate Proton Calendar: No account needed
Threat level
Covered
A covered pick. Anyone can use it as a private drop-in, with no setup or know-how. Enough for most people. Threat levels
Our take
An end-to-end encrypted calendar where even event details and titles are hidden from the provider, which is rare and genuinely valuable, especially if you already live in the Proton ecosystem. The honest limits are practical: the best features sit behind a paid plan, and a fully encrypted calendar trades away some of the slick sharing and integration you get from Google. Pick it if you treat your schedule as sensitive data. Mainstream convenience seekers may find it more locked-down than they expect.
GitHub at a glance
ProtonMail/WebClients
Stars
5,505
+ 53 this week
Last commit
8d ago
healthy
License
GPL-3.0
Latest release
proton-authenticator@1.1.6
1mo ago
Stars, last 31d
Website at a glance
proton.me
B+ score 80
Solid website security headers
Graded by Mozilla HTTP Observatory, tested 14d ago
Inspect this site yourself
Measures the security configuration of the tool's own website, not the privacy of the product itself. A strong tool can still score low here.
Proton Calendar alternatives
Tuta Tuta: Free, Cross-Platform and Zero-Knowledge Calendar
EteSync If you decide to self-host EteSync you won't have to pay for the subscription. Tutorial here .
Radicale A simple self-hosted CalDAV and CardDAV server for calendars and contacts, written in Python and licensed under GPLv3.
Peergos Audited by Cure53 in May 2019.
Proton Calendar license, in plain English
GPL-3.0 Strong copyleft
Free to use and modify, but anything you distribute that is built on it must also be open under the same license.
Permits
- Commercial use
- Modification
- Distribution
- Patent use
- Private use
Requires
- Disclose source
- Same license
- State changes
- License and copyright notice
Does not provide
- Liability cover
- Warranty
Why it matters: Strong copyleft keeps every distributed version open. A vendor cannot fold this into a closed product and ship it without releasing their changes.
Plain-language summary of the project's license, not legal advice. Read the full text for the exact terms.
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