Receivables that cannot drift

One self-contained HTML file — no build, no server, no persistence. It is dressed as the working product: a tenant list, a statement panel, an aged-debt report and a ledger. Every action writes an entry to that ledger, and none of them can be taken back.

The question: can rent collection be run as a set of books rather than a running total? Anyone can render an invoice. The doubt worth answering is what happens to the awkward money — the payment that is deliberately 5% short, the round number that does not match any invoice, the charge that is disputed after it was issued.

One prototype, built deep, for the same reason as the other two Operations sets. The interesting part is not the layout; it is whether the books still agree with the bills after you have tried to confuse them.

How to drive it. Pick a tenant, pick a bill, and record something on the right — a payment, a certificate, a credit note. The Demo drawer along the bottom holds five guided scenarios and a live list of what it guarantees, and resets the books to September 2026.

1. 01 CollectionsPrototype Casa Verde Property Management · three tenants · four months of books

   Every change written down twice, counted in whole centavos, and never edited afterwards. A company tenant holds back 5% of the rent and pays it to the BIR itself, so the money that lands is short on purpose — the bill reads awaiting-certificate rather than overdue, and clears when the BIR 2307 arrives. A round-number payment goes against the oldest bill first, and whatever is left over is held as that tenant’s credit. A disputed charge gets a credit note, because there is no way to edit a bill that already went out. Late fees are added alongside rather than folded in, so the original bill still reads exactly as it was sent.

   Doubt

   Can they handle money?

   Model

   Nothing is ever edited; every figure is worked out from what actually happened

   Proof

   Six checks, including that the unpaid bills and the books always agree