How cloud sync works

Manga Vault stores your data in the cloud so it syncs across all your devices and stays safe even if you lose your phone. Here’s how cloud sync works.

What syncs to the cloud

Your collection — Every owned and wishlisted volume, with their conditions, custom values, quantities, and reading progress.
Your shelves — Every shelf you’ve created, with which volumes are on it.
Your reading progress — Current page, status (Unread/Reading/Completed), times read, started/finished timestamps.
Your profile — Display name, username, bio, avatar, cover image, favorite genres, privacy settings.
Your friends — Friend list, pending and sent requests.
Your achievements — Unlocked achievements and XP.
Your gamification stats — Streaks, total scans, level info.
Your lending records — Active and returned loans.
Your subscription status — PRO or FREE, expiration date.

What’s local-only

A few things stay only on your device:

App preferences (sort order, view mode, filter selections) — these sync but are also locally cached.
Local cache of cover art and catalog data.

If you sign out and back in, locally-cached preferences may not return — that’s expected.

When sync happens

On app launch — Pulls latest data from the cloud and pushes any pending local changes.
On returning from background — Same.
After most actions — Adding a volume, marking as read, etc., trigger a near-real-time sync.
On pull-to-refresh — Manual full sync.

Conflict resolution

If you make changes on two devices simultaneously (e.g., add a volume on your phone and a different volume on your tablet at the same time), Manga Vault uses timestamp-based merging to resolve:

The most recently modified version of each field wins.
For shelves (which are tag-like), we use union merging — your shelf assignments from both devices are combined, never replaced. This prevents accidental shelf-loss during sync.
Deletions are respected — if you deleted a volume on one device, it stays deleted across.

Pending changes

When you’re offline or temporarily unable to reach our servers, your changes queue up locally as pending changes. The next time you have a connection, they sync automatically.

Pending changes are persisted to disk so you don’t lose them if the app force-closes or your phone restarts.

Cross-device sync

Sync security

All sync data is sent over HTTPS (encrypted in transit). Our servers store your data encrypted at rest in AWS. Only you can read your own data — friends see what you’ve made visible via privacy settings, but that filtering happens server-side.

Where data lives

Manga Vault uses AWS infrastructure:

Cognito — Account authentication.
DynamoDB — Your collection and account data.
S3 + CloudFront — Catalog data and uploaded images.
Lambda — Backend processing.

We don’t sell your data. We don’t share it with third parties for advertising.

Sync status

The Settings screen has a Sync Status section (when relevant) that shows when your last sync happened and any pending changes count.

What if sync breaks?

See Sync failure banner and Working offline.

Privacy

Friends never see your data unless you allow it via privacy toggles. We never look at individual user data except in support cases (and only with your explicit permission).