Advanced Finance Tracker — offline-first personal finance app

The problem

Most finance apps keep the user's ledger only in the cloud, so the app is slow without a connection and the data depends on a remote server.

Advanced Finance Tracker keeps the ledger on the phone and treats the cloud as an optional sync target.

Architecture and approach

• Mobile client in React Native with Expo and Expo Router, storing every record in an embedded SQLite database with schema migrations.
• NestJS API with Prisma and PostgreSQL acting as the sync engine for multiple devices, with offline change queuing.
• pnpm monorepo with shared packages for TypeScript types, Zod validation schemas, a typed API client and configuration.

Key features

• Accounts (bank, cash, cards, savings), multi-currency balances and transfers between accounts.
• Income/expense ledger with recurring rules, budgets per category and savings goals.
• Lending and borrowing tracking.
• Scoped soft-deletion (month, year or all-time) that propagates through sync.

Engineering decisions

• Money is handled as integer/scaled-decimal strings rather than floating point, so totals never accumulate rounding errors.
• Deletions are soft-delete tombstones (deleted_at) that sync to the server, so a record deleted on one device cannot be resurrected by another device's sync.
• Parameterised SQL everywhere on the device database.

Technology stack

Mobile

• React Native
• Expo
• Expo Router
• TypeScript
• SQLite (expo-sqlite)

Backend

• NestJS
• Prisma
• PostgreSQL
• Redis

Tooling

• pnpm workspaces
• Zod
• Jest
• ESLint

Links