Rentals without spreadsheets, with an assistant that understands your numbers.

The problem

People with a few rented flats usually manage them in a spreadsheet. That works until you need to raise the rent in line with inflation, find out which tenant owes money, work out what each property really earns or prepare your tax return.

What I did

All of it: the Android and iOS app, the web app, the admin panel, the server and the store releases.

• 38 screens in the app, and a web app with the same features on the same backend.
• ClaraAI, an assistant with 50 tools that reads and changes your data. Before changing anything, it shows you what it is about to do and waits for your approval.
• Tax report for Spanish personal and corporate income tax, in PDF and Excel.
• Rent updates using the official indices of Spain’s statistics office (INE), with the letter to the tenant already written.
• Alerts for late payments and expiring leases, and returns per property.
• Free, Pro and Max subscriptions.

Three decisions

1. Several AI providers behind a single interface. Anthropic, Gemini and DeepSeek: the model is chosen per plan from the admin panel, there is automatic fallback if one fails, and spending is controlled on the server.
2. The app works offline. Data is stored on the phone and refreshed in the background, so it shows up instantly even without a connection.
3. An admin panel that can’t break anything. It connects to the database in read-only mode. Anything that changes data goes through server functions, and anything that affects real users asks you to type PROD, which the server checks again.

And the infrastructure

My own server, encrypted backups every six hours, Android and iOS builds on my own machines, and a server migration with about four minutes of downtime.