HisaabKitaab: bill splitting that settles over UPI

Why I built it

Splitwise moved features behind a paywall, and it never handled the part Indians care about most, which is paying each other back over UPI. I wanted a free app where working out who owes whom and settling up happen in the same place.

My role

• Wrote a 22-section PRD covering personas, success metrics, scope, user flows, data model, API contracts, the UPI integration design, security, release phases, risks and a handoff checklist for the coding agent.
• Directed an AI coding agent (Amazon Quick) that wrote the code from the PRD.
• Ran every build, type-check, database migration, deploy and release myself.

What it does

• Groups for flatmates, trips and office lunches, plus one-on-one tracking with a friend.
• Splits equally, by exact amounts, by percentage, by shares, or by item for restaurant bills, with several payers and recurring bills.
• Works out the fewest payments needed to clear a group, then lets you pay in one tap with GPay, PhonePe, Paytm or BHIM, or with a QR code.
• Sends WhatsApp reminders, handles 16 currencies for travel, works offline, sends web-push notifications, and installs to the home screen.

Product decisions

• A payment counts only when the person paid confirms it. Database triggers keep a payment pending until the payee confirms it, so one side can't settle a balance alone.
• Settling up takes as few payments as possible. The app nets each person's balance and matches the biggest debtor with the biggest creditor until everything clears, so a tangle of expenses becomes a handful of "pay X to Y" steps.
• The database enforces privacy. Membership-based row-level security means only people in a group can read it.
• Offline edits never create duplicates. Every change goes through a saved outbox and replays in order as an idempotent write when the connection returns.

Release history