It started with distrust. I'd been using a couple of popular finance apps — the kind you sign up for, link your bank, and hope for the best. They worked fine. But there was always this low-level discomfort: somewhere on a server I've never seen, in a database I'll never inspect, sits every salary credit, every embarrassing impulse purchase, every month I blew the grocery budget. That felt wrong. So I built my own. This is the story of how it works, the decisions I made, and the things that surprised me along the way. The Constraint That Shaped Everything Before writing a single line of code, I made one rule: The app will have no backend. My data stays in my Google account. That sounds simple. It isn't. Almost every interesting feature in a finance app — sync, multi-device access, historical data — assumes a server somewhere. Removing the server meant I had to find creative replacements for things I'd been taking for granted. The answer turned out to be something hiding in plain sight: Google Sheets .…