I Built a Free Debt Payoff App - Here's What I Wish I Knew About Personal Finance APIs

Luis Tannous — Tue, 26 May 2026 23:25:43 +0000

A few months ago, I got tired of juggling multiple spreadsheets to track my debt payoff journey. So I built The Golden Grizzly (thegoldengrizzly.com) — a focused debt management app. Here's what I learned building it, especially around the challenge of connecting to financial data.

The Problem: Most Finance Apps Try to Do Everything

Mint, YNAB, Personal Capital — they're great apps, but they try to be everything: budgeting, investing, net worth tracking, and debt management all in one. The problem? When your main goal is getting out of debt, you need laser focus, not feature bloat.

I wanted to build something that only does one thing: help you visualize and execute your debt payoff strategy, whether snowball or avalanche.

The Tech Stack

The app is built with a modern web stack:

Frontend: React + TypeScript
Backend: Supabase (PostgreSQL + Auth)
Payments: Stripe
Bank connectivity: SimpleFIN Bridge

The Hardest Part: Connecting to Bank Data

This is where things get interesting for devs. Most financial APIs (Plaid, MX, Finicity) charge $500+/month for production access. That's a non-starter for a bootstrapped app.

Enter SimpleFIN Bridge — an open, user-controlled protocol that lets users share their own financial data without giving a third party full access to their accounts. The user sets up a SimpleFIN Bridge access URL themselves, and your app reads from it. It's privacy-preserving and costs pennies.

The integration looks roughly like:

// User provides their SimpleFIN bridge URL
const response = await fetch(simplefinBridgeUrl);
const accounts = await response.json();
// Map accounts to debt objects in your app

Much simpler than OAuth flows with Plaid, and users understand exactly what they're sharing.

The Debt Algorithms

Implementing snowball vs. avalanche was surprisingly fun. Both algorithms take the same inputs (debts with balance, APR, minimum payment) and produce a payoff schedule, but with different ordering:

Snowball: Sort by balance ascending, attack smallest first
Avalanche: Sort by APR descending, attack highest interest first

The visual calendar that shows projected payoff dates ended up being the most-praised feature in user testing.

The Free Tier Strategy

I made a deliberate choice: the free plan lets users track up to 3 debts forever. No credit card required, no expiring trial. The paid Gold Member plan ($4.99/month) unlocks unlimited debts, bank sync via SimpleFIN, AI-powered insights, and smart payment reminders.

The reasoning: most people with serious debt anxiety have more than 3 debts. Letting them start free, see the value, and then upgrade when they're ready to tackle everything has been the right call.

Try It

If you're dealing with debt yourself or building something in the fintech space, check it out at thegoldengrizzly.com. Feedback from devs especially welcome — there's a lot of interesting technical ground to cover in this space.

Happy to answer questions about the SimpleFIN integration or the debt calculation algorithms in the comments.