MoneyKoi Budget book app

After more than ten years of managing my own finances I wanted a budget book without a bank login, without cloud AI and without ads, that does everything in airplane mode. Today MoneyKoi comes as Free, Pro and Cloud plans: without an account the whole book lives on the phone; with Cloud a household shares one book across phones, tablets and the browser.

1. 01

   The local database is the source of truth

   The app reads and writes only to SQLite. Changes go into a persistent outbox that pushes them one at a time, coalesced and with retries. Changes from other devices come back through a single delta sync; realtime events only trigger a pull, and the data itself always arrives the same way.

2. 02

   A budget book is a tenant

   Before every request a PostgREST hook checks that the user is a member of the book. Row-level security is deliberately asymmetric: reads are limited to the active book, writes are checked against the row's own book. Bookings queued offline still go through after the user has switched to another book.

3. 03

   The receipt scanner stays on the device

   ML Kit reads text and QR codes on the phone, shop-specific parsers for SPAR, BILLA, Lidl and others extract the line items, and a reconciler checks that they add up to the total. All rule-based, no LLM – the photo and its text are never sent to an AI service.

4. 04

   No floats for money

   Amounts are NUMERIC on the server and a Decimal value object in Dart; triggers maintain balances incrementally. The forecast, recurrence rules and loan maths exist in both Dart and TypeScript – shared test fixtures make sure app and web return exactly the same numbers.

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