I Resurrected Malaysia's Buku 555 Debt Notebook with Kiro

This post is part of a contribution for the Kiroween 2026 hackathon competition. The hackathon focused on resurrecting Malaysia's iconic Buku 555 debt notebook, traditionally used by market traders to track credit given to regular customers. The notebook, known for its durability issues in wet conditions and frequent page loss, was brought back to life in a new form called Buku 555 Berhantu, or the haunted debt book.

When used, a trader inputs entries in Bahasa Melayu, such as "Kak Ros ambil 2 kilo kembung RM18, bayar Jumaat," which the Malay parser extracts information like customer, item, amount in Ringgit Malaysia, and the due date, including honorifics and Malay number words. Overdue customers are accompanied by a friendly ghost, and a single tap prepares a polite reminder in WhatsApp, with the trader confirming the reminder by pressing 'send.'

No automatic reminders are sent, and marking a debt as paid exorcises the ghost. The system was designed with a 60-year-old fish seller in mind, featuring Malay-first design elements, large tap targets, no login requirements, no server dependence, and offline functionality post-installation.

The creation process utilized the Kiro CLI and adhered to a spec-first approach. Steering documents outlining Malay-first copy, absence of server or tracking mechanisms, and large buttons for older traders were created prior to any coding. Kiro used these documents to guide the development process, ultimately generating three spec files: requirements.md containing user stories, design.md detailing the data model, parser grammar, and correctness properties, and tasks.md listing tasks from T-1 to T-27.

Two key agents supported the development process: run-tests-on-save, which automatically tests JavaScript files upon modification and fixes failures without compromising tests, and i18n-check, ensuring every string in the i18n.js file has both Malay and English versions. Property-based testing was also employed to validate correctness properties, including preventing negative amounts, ensuring total outstanding matches unpaid entries, and verifying total reduction upon marking an entry as paid.

These tests caught edge cases that would have otherwise gone unnoticed with hand-written unit tests.

The author of the project learned that spec-driven development initially seemed slower but became much faster as the requirements and properties were explicitly documented. This allowed Kiro to independently verify its work, while the author focused on improving the trader's experience and making the debt chasing process less awkward. The demo and code for the project are available at the provided links for exploration and interaction.