Saifullah AhadHow I built it
Simpulan: Untangle DebtsLive on Google PlaySimpulan: making loops of debt disappear
Untangle Debts, live on Google Play. Friends and family cancel debts that go in a circle — and no money ever moves.
01
The problem
People end up owing each other in loops. You owe your cousin, your cousin owes the corner shop, and the corner shop owes you. The three debts cancel perfectly, but nobody can see it, because each person only knows their own side.
02
The plan I wrote
Each person records what they owe and are owed. The other person taps once to agree, and after that neither of them can change the record.
The app searches the whole group for loops and tells everyone in one: this much can disappear right now, you end up exactly as well off as before, and nobody pays anybody. A clearing happens only when every person in the loop approves it. No money ever moves through the app.
03
The build
AI coding agents built it from my written specification. My work was the specification, the tests it had to pass, and the review.
04
The proof
The signed release build passed on both test devices — an Infinix phone and a Galaxy Tab S3 — including a real two-person pairing, agreement on both sides, and a clearing that everyone approved, all still there after a cold restart.
The security checks passed too: sessions renew themselves, and replayed or forged requests are refused. Zero crashes on either device.
05
The launch
Live on Google Play, with its privacy policy, child-safety standards and store listing checked before release.
What this shows about how I work
- Fairness by design: nothing changes unless everyone agrees.
- Security proven, not assumed: replayed and forged requests are refused.
- A hard group problem made simple: one number, one tap.
How to settle who owes who in a group
Debts between friends and family often go in a circle without anyone noticing:
- Write down every debt, and have both people agree it is right.
- Look for loops. You owe your cousin, your cousin owes the shop, the shop owes you.
- Cancel the smallest amount in the loop for everyone. Each person ends up exactly as well off as before.
- Cancel only when everyone in the loop agrees. Nobody pays anybody for that part.
Simpulan does this for the whole group: each record is agreed by both sides and cannot be quietly changed, the app searches for loops, and a clearing happens only when every person in the loop approves it. No money ever moves through the app.
More build stories: How to check a used phone before buying · How to check if your electricity meter is running fast · Eelj: a fair turn for a village’s one harvester · Practicing stuttering techniques at home · Where and when to look for the new crescent moon · How to split electricity bill with roommates · Milk fat SNF rate calculator, step by step · How to check a link before you click it · How to calculate cattle weight without a scale · Braille translator that explains every cell · Math learning gaps: where to start when a child is stuck · How to describe a car noise so a mechanic can find it · Convert Rumi to Jawi, then check the spelling · How to sync SRT subtitles with video · How to measure land area with phone GPS · Quran pronunciation app, tap any word to hear it · Lipi: Bangla keyboard, side by side with Ridmik · How to check an overseas employment contract · Extract data from graph image on Android · VaporSill: how to tell if damp or condensation · Dinig: doorbell alert for deaf · GlyphFlow: reading apps for dyslexia adults · Tnixxif: how to dry rice after harvesting · Lohkat: kids reading practice at home · PayProof: employer not paying salary, what to do · Oinordetza: how to divide inheritance in Islam · Energy Loom: how to calculate battery backup time · How to find dead spots in wifi, room by room · Beehive inspection checklist: what to check and how often
Open to work
Let's build your AI product system.
Full-time roles — remote anywhere, hybrid in Bangladesh, or on-site abroad: AI Product Builder, AI Product Manager, AI Workflow Orchestrator, Product Delivery Lead.
Based in Dhaka, Bangladesh (UTC+6) · works any time zone · can start now · ready to relocate with visa sponsorship.