KMP sync — Supabase + PowerSync for offline-first cross-platform
2026-04-07 summary kotlinkmpsyncoffline-firstsupabasepowersyncmobile
Key Takeaways
For family/cross-platform apps needing offline-first sync between Android + iOS: Supabase + PowerSync is the recommended stack. MongoDB Realm Sync was deprecated Sep 2025 — no longer an option.
| Solution | Offline-First | MVP Timeline | 5K MAU Cost |
|---|---|---|---|
| Supabase + PowerSync | Native | 1-2 weeks | ~$75/mo |
| Firebase (GitLive) | Cache only | 1 week | Free-$25/mo |
| Couchbase (Kotbase) | Native | 2-3 weeks | Free-$50/mo |
| Supabase alone | None | 3-5 days | $25/mo |
PowerSync maintains local SQLite on each device, syncs bidirectionally with Supabase Postgres. supabase-kt SDK (v3.3.0) provides full KMP support.
If budget is tight and offline isn’t critical: Firebase via GitLive SDK (simpler, online-first with cache).
Connections
- privacy-as-architecture — local SQLite + selective sync = user controls what data leaves device
- infra-two-tools — Supabase as backend aligns with the shared auth infrastructure