Daybook: Privacy-Centric Personal Finance & Expense Tracker
Instant expense logging through automated SMS transaction parsing, biometric authentication, and an encrypted offline-first SQLite database.
Key Project Metrics and Results
01 / System Overview
Background & Problem Space
Users abandon expense tracking apps because manual entry is tedious, and cloud-first personal finance apps jeopardize user financial privacy. Daybook automates the friction of expense tracking by reading transactional bank SMS locally and storing all financial records inside an encrypted on-device SQLite database.
02 / Technical Challenge
Core Bottlenecks
Bank and UPI transaction SMS messages come in hundreds of unstructured formats from dozens of financial institutions. The app must parse merchants, amounts, debit/credit types, and account balances accurately on-device without sending sensitive messages to an external server.
03 / Engineering Solution
Architectural Approach
We developed an intelligent on-device regex parsing engine in React Native that categorizes expenses instantly upon SMS arrival. Daybook is fortified with biometric Face ID / Fingerprint locking, zero-knowledge cloud backup, and interactive budget visualizations.
04 / Architecture Breakdown
Key Engineering Decisions
Local-first React Native Expo mobile architecture powered by an embedded SQLite database, background task workers for SMS ingestion, and optional encrypted Supabase cloud synchronization.
On-Device SMS Parsing: All SMS transaction parsing occurs directly within the phone OS sandbox. No raw SMS text ever leaves the user’s device.
Biometric Secure Store: App launch requires local authentication via Face ID or Fingerprint; encryption keys reside securely in iOS Keychain / Android Keystore.
Instant Offline Ledger: High-performance SQLite database delivers silky 120fps chart animations and instantaneous search across years of historical transactions.
05 / Delivered Ecosystem Modules
Full Multi-Module System (4 Applications & Services)
Every client, role, and stakeholder received a purpose-built application engineered for their specific workflow.
Daybook Cross-Platform Mobile App
Fluid mobile application featuring interactive monthly budget wheels, category breakdown bar charts, and quick manual transaction inputs.
Technical Highlights:
- ✦120fps fluid chart animations
- ✦Custom category & tag creation
- ✦Dark / light theme adaptation
Automated Bank SMS Parser Engine
On-device parsing module that monitors incoming bank and UPI debit alerts, extracting the merchant name and exact amount with zero manual intervention.
Technical Highlights:
- ✦Multi-bank format heuristics
- ✦Zero-cloud local privacy
- ✦Duplicate transaction avoidance
Biometric Security Module
Hardware-backed biometric lock that shields financial data with Face ID and Fingerprint authentication whenever the app is backgrounded.
Technical Highlights:
- ✦Instant auto-lock on app minimize
- ✦Keychain-secured encryption keys
- ✦Haptic feedback on authentication
Offline-First SQLite Ledger Database
Embedded SQL database allowing users to query, filter, and export thousands of transactions without requiring an active internet connection.
Technical Highlights:
- ✦Instant sub-millisecond queries
- ✦CSV & Excel statement export
- ✦Automated recurring bills scheduler
Core Technology Stack
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