Replaces a shopkeeper’s paper udhaar book with a running per-customer balance and reminders that settle themselves.
A ledger app for shops and small businesses: daily income and expenses, udhaar with a running balance per contact, and payment reminders that settle themselves into real ledger entries when they come due.
Source private
Industry
Retail / SMB Finance
Role
Architect & Full-Stack Engineer
Type
Mobile App
Year
2026
Status
Delivered
Mobile + Web + Admin
Surfaces
Offline-first
Storage
4
Entry Types
Overview
Khatapatra is a digital khata for shopkeepers — the paper ledger, kept properly. It tracks daily income and expenses, and handles udhaar (informal lending) with a running balance per contact, so a shopkeeper always knows both the day's position and who still owes them.
The distinguishing detail is that reminders are not notifications. When a payment reminder comes due and is settled, it becomes a real ledger entry rather than a note the user has to re-enter — the reminder and the accounting are the same object, so the balance stays correct without double-entry by hand.
One NestJS API serves three surfaces: a Flutter mobile app for shopkeepers built offline-first on sqflite, a Next.js marketing site, and a super-admin panel.
The problem
Shopkeepers track income, expenses and udhaar in paper ledgers. Balances drift, who-owes-what is reconstructed from memory, and payment reminders — when they exist at all — are separate from the accounting, so settling one means re-entering it as a transaction.
The solution
A ledger app modelled on how a khata is actually kept: entries by type, a running balance per contact for lending, and reminders that resolve into ledger entries when settled so the books stay correct without duplicate data entry.
Technical stack
Frontend
Flutter
Riverpod
Next.js 15
Tailwind CSS 4
Backend
NestJS 11
Data
sqflite
MySQL 8
Also used
Prisma
Dio
System architecture
1
NestJS 11 API over Prisma and MySQL 8, serving all three surfaces from one contract
2
Flutter mobile app with Riverpod state and sqflite for offline-first storage, syncing through Dio
3
Next.js 15 web app doubling as the marketing site and the super-admin panel
4
Seeded demo book with entries, contacts and reminders for evaluation
Engineering challenges
Challenge
A reminder and the transaction that settles it are usually separate records, so settling a reminder leaves the ledger untouched until someone re-enters the amount.
How I solved it
Modelled the reminder as a pending ledger entry rather than a notification, so settling it commits the entry directly and the running balance updates without a second manual step.
Challenge
Shop connectivity is unreliable, and a ledger that refuses to record a sale because the network is down is worse than paper.
How I solved it
Built the mobile app offline-first on sqflite — entries are written locally and reconciled with the API when connectivity returns, so the ledger is always writable.
Core features
Daily income and expense ledger with four entry types
Udhaar tracking with a running balance per contact
Payment reminders that settle into real ledger entries
Offline-first mobile storage with sqflite
Reports over the ledger period
Multi-book support per business
Super-admin panel over the same API
JWT auth with role separation
Results & impact
A shopkeeper gets the day's in/out position and a per-contact udhaar balance in one place, with reminders that keep the books correct when they settle — and the app keeps working when the connection does not.
Screenshots
What I learned
Modelling a reminder as a pending entry rather than a notification removed an entire class of reconciliation bugs.
For users whose alternative is paper, offline-first is not a feature — it is the minimum bar for being trusted with the data.
