Ask people why they don't track their spending and you hear the same reasons: budget apps feel heavy, many want bank logins, and nobody wants their salary sitting readable on a company's server. Then there are shared costs (trips, PG rent, flat bills) living in WhatsApp threads where someone is always out of pocket.
Hisab is our answer: one app to track spending and split costs, built so that even we can't read your money. Here's what building it taught us.
1. Make privacy structural, not a promise
A privacy policy is a promise. Encryption is a fact. In Hisab, every amount, merchant and note is encrypted on the phone with AES-256-GCM before it leaves, so the server holds only ciphertext. Each person's key is backed up to their own Google Drive, never to our servers.
If the server can't read the data, it can't leak it, sell it or be forced to hand it over.
2. Privacy must not cost simplicity
Strong security often makes products painful. We refused that trade. Unlocking uses a PIN or fingerprint people already know; adding a spend takes seconds, with bank SMS that fills itself in. The encryption is invisible; the calm is not.
3. Use words people already trust
We used words from the payment apps people use every day: Split, Spent, Bills. Familiar language lowers the effort of learning something new, and it signals that the app works the way people expect.
4. Design for real life, not the textbook
Splitting is never just "equally". Trips, PG rooms and messes split by amount, percentage or shares. Debts settle with the fewest payments, each a one-tap UPI link, and each person's share flows into their own spending report.
Products win when they handle the messy cases people actually live with.
5. Prove it with tests
Claims like "secure" and "accessible" mean little without evidence. Hisab has 48 unit tests on encryption, splitting and imports, 15 security rule test suites, and zero accessibility violations across 32 screens in light and dark mode. Our heuristic evaluation found 8 issues; all 8 are fixed.
What this means for your product
If your product handles money, health or personal data, privacy can be a feature people feel, not just a page they never read. Build it into the architecture, keep the experience simple, and test what you promise.
Handling sensitive data in your product? Talk to us about designing privacy in from the start.
- Make privacy structural: if the server can't read data, it can't leak it.
- Borrow the words people already know from apps they trust.
- Prove what you promise with tests, not adjectives.