Proton, CalDAV/CardDAV, and Android sync

Most people who end up reading this want one simple thing: their Proton Contacts and Proton Calendar showing up in the apps they already use on Android — the system Contacts app, the dialer, Google or Samsung Calendar, their watch — and staying in sync. On most providers you’d reach for DAVx5. With Proton, that route is closed. This explains why, and what works instead.

Does Proton support CalDAV or CardDAV?

No — there is no CalDAV or CardDAV endpoint to connect to. CalDAV (calendars) and CardDAV (contacts) are the open protocols that let apps like Apple Calendar, Thunderbird or DAVx5 read and write your data on a server. Proton doesn’t expose one.

What Proton does offer is narrower:

• Proton Calendar lets you share a calendar via a view-only link that other apps can display, and export/import calendars as .ics files.
• Proton Contacts lets you export and import contacts as vCard.

None of that is live two-way sync, and none of it lets a third-party Android app sync against your Proton account. This is the situation as of June 2026; Proton could add CalDAV/CardDAV in future — it has been requested for years on Proton’s own feedback forum and is still not shipped.

Why DAVx5 can’t reach Proton

DAVx5 is a CalDAV/CardDAV client. It is excellent at what it does, but it needs a server that speaks those protocols to connect to — a Nextcloud, a Fastmail, an iCloud, a generic CalDAV/CardDAV host. Proton is none of those, and Proton does not appear on DAVx5’s list of tested providers. There is simply nothing for DAVx5 to point at.

So “DAVx5 + Proton” isn’t a setup you can fix with the right server URL. The endpoint doesn’t exist.

Why doesn’t Proton just add it?

The explanation usually given is Proton’s end-to-end, zero-access encryption: Proton’s servers can’t read your calendar events or contacts, while CalDAV/CardDAV are server-side protocols that expect the server to read and edit that data. Those two designs are hard to reconcile.

The realistic options

1. A view-only calendar share link. Proton lets you share a calendar via a link another app can display, but it’s read-only, calendar-only, and not real sync.
2. Manual vCard/.ics export and import. A one-time snapshot that goes stale the moment anything changes. Fine for a migration, not for living data.
3. Unofficial bridges. Open-source projects (for example ferroxide and hydroxide) reverse-engineer Proton’s API and expose a local CalDAV/CardDAV server that DAVx5 can then talk to. They can work, but they are unofficial, unsupported by Proton, and you run and trust the bridge yourself. Worth knowing they exist; not for everyone.
4. A native sync adapter — Sync Provider for Proton. Rather than wait for a DAV endpoint, it talks to Proton’s own API directly and writes your contacts and events into Android’s system Contacts and Calendar — two-way, on a schedule, with no server to run.

The trade-off worth understanding

For your Proton contacts to show the right name when someone calls, and your Proton events to appear on your lock screen and watch, the data has to be decrypted and handed to Android’s system providers — where it then lives like any other contact or event. That is true of every sync adapter on Android, Google’s and Samsung’s included.

Sync Provider encrypts credentials at rest and only ever talks to Proton’s API, but the synced data itself lives in Android’s providers by design — that’s what makes it usable everywhere. If you’d rather nothing touched those providers, Proton’s own apps keep everything in-app. The Data & Encryption section on the main page spells out exactly what is stored and where.

In short

• Proton has no CalDAV/CardDAV today.
• DAVx5 can’t reach Proton because there’s no endpoint to connect to.
• Sync Provider syncs via Proton’s API into Android’s own Contacts and Calendar — two-way, no server, on standard Android and on GrapheneOS.

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