Why a note app is secretly hard

A note app looks like a weekend project until you need offline-first sync. The moment users expect to write a note on the plane and have it show up on their laptop, you are building a conflict resolver, not a form. I hit this on one of my four apps and spent three days on sync alone.

AI is the easy win on top: a "summarize this note" button is genuinely useful and takes an afternoon to wire.

What you actually need to build

• Notes list + detail: Plain text first. Markdown in v1.1. Rich text (bold, images, tables) is v2.
• Offline-first write: The app must work with no network. Write to local storage immediately, queue a sync when online.
• Conflict resolution: Last-write-wins based on updated_at is fine for a personal note app. You do not need CRDTs on v1.
• Search: Full-text search across all notes. Postgres tsvector on the server, local fallback for offline.
• AI summarize: One button on a note that returns a 3-bullet summary. One call per summary, cached on note_hash so repeated taps do not cost again.
• Folder or tag: Pick one. Not both in v1. I picked tags on my app because folders are harder to sync.

The stack I use

• React Native + Expo.
• Supabase — auth, notes table, Postgres full-text search.
• expo-sqlite for local storage and offline writes.
• A sync reducer that replays queued writes on reconnect.
• NestJS — the summarize endpoint with per-user quota.
• Claude Code + 11 AI agents — scaffold the note list, editor, and summary panel.

Real build time

With the boilerplate, first note app in 3 weekends.

• Local SQLite + write queue: ~8 hours.
• Sync reducer + conflict resolution: ~6 hours.
• Notes list, detail, editor: ~6 hours.
• Full-text search (Postgres + local): ~4 hours.
• AI summarize button + cache: ~3 hours.
• Store submission + iCloud backup copy in review notes: ~5 hours.

About 32 hours. The sync layer is most of it.

Where people get stuck

• Write race when typing fast: User types while a sync is mid-flight. Without a proper queue, the sync overwrites in-progress text. Always queue writes as discrete ops, never as a "current note state".
• Startup latency from pulling all notes: Once a user has 500 notes, pulling all of them on launch takes seconds. Paginate on updated_at desc and load the rest in the background.
• AI cost runaway: Without caching on note_hash, summarizing the same note twice costs twice. The cache layer cuts cost by roughly 50% in casual use.

Skip the setup

Offline write queue, Supabase schema with full-text search, summarize endpoint with cache — pre-wired. The 11 AI agents scaffold the editor and list screens.

See pricing