I'm in 8th grade and I built a fintech app. Here's what I learned.

#webdev #ai #javascript #beginners

I'm in 8th grade and I built a fintech app. Here's what I learned.

I'm 13 years old and I just shipped a real product.

It's called Think to Buy — a web app that tells you whether you can actually afford something before you buy it. You can try it at himothyjimothy17-tech.github.io/Think-To-Buy

Here's the story of how it happened and what I learned building it.

Why I built it

I kept noticing something. People around me — including people I know — would buy things without thinking about whether they could afford it. Buy something, regret it, repeat.

At the same time I realized nobody actually teaches young people how money works. Not in school, not really at home. There's this massive gap between what people know about personal finance and what they actually need to know.

So I decided to build something that closes both gaps at once — a tool that helps you make smarter spending decisions, and also teaches you the financial concepts behind those decisions.

What it does

The core feature is simple. You type what you're thinking of buying — something like "thinking of buying AirPods for $249" — and it instantly tells you:

Whether you can afford it (green, yellow, or red verdict)
What percentage of your savings it uses
How many weeks of income it takes to recover
Where to buy it cheapest, with the brand's official store first

But it grew into a lot more than that:

Compare mode — type two products and get a real side-by-side comparison with actual specs, pros and cons, and a clear recommendation. It pulls nutritional data from Open Food Facts for food items, and uses AI for everything else.

Financial education — 8 lessons on things school never taught me. Taxes, compound interest, how investing actually works, credit scores, how business and profit work, inflation, budgeting, retirement. Each lesson has a real-world example and a quiz.

AI advisor — answers any money question based on your actual numbers. Uses a rules-based system for common questions (instant, no API call) and Groq + Llama 3.3 for complex ones.

Spending dashboard — tracks money you saved by saying no, compares your spending against the 50/30/20 rule, shows charts over time.

Plus goals, bills, markets with live charts, a streak tracker, shareable verdict cards, and currency auto-detection for 30+ countries.

The tech

Here's the part that might surprise you.

The entire app is a single HTML file.

No React. No Vue. No build step. No framework. Just vanilla HTML, CSS, and JavaScript. The whole thing runs in a browser with no installation.

The stack:

Supabase for auth and database
Groq API (Llama 3.3 70B) for AI
Chart.js and TradingView for charts
Open Food Facts API for nutrition data
Wikipedia API for product info
Netlify for hosting

I chose this approach because I wanted to ship something real, fast. No setup, no toolchain, no configuration. Just open a file and it works.

What I actually learned

Shipping is harder than building.

The hardest part wasn't writing the code. It was making decisions. What features to cut. What to prioritize. When something is good enough to ship versus when it needs more work.

Users find bugs you never imagined.

I tested this app hundreds of times. The moment other people used it, they immediately found things I never thought of. A button that didn't work in a certain order. A feature that made no sense without context. An edge case I'd never considered.

Product decisions are harder than technical ones.

Should the advisor use AI or rules? Should the history tab show a list or a dashboard? Should store suggestions be smart or just show everything? None of these have obvious answers. You have to think about what actually helps the user.

A single HTML file can do a lot.

People assume modern web apps need a framework, a build system, TypeScript, and a CI/CD pipeline. I built something with auth, cloud sync, AI, live charts, and real-time data in a single file. Sometimes simple is better.

Financial literacy is a bigger problem than I realized.

The more I built the education features, the more I realized how much I didn't know. Taxes, compound interest, how credit scores actually work — none of this gets taught properly. Building the lessons taught me as much as it'll teach users.

What's next

I'm launching on Product Hunt this Tuesday. The investment club at a local school is going to demo it to their members. And I'm going to keep iterating based on what real users tell me.

If you try it, I'd genuinely love to hear what you think. What's confusing? What's missing? What would make it actually useful for you?

Try it: himothyjimothy17-tech.github.io/Think-To-Buy

GitHub: github.com/himothyjimothy17-tech/Think-To-Buy

I'm 13 and this is my first real shipped product. Be honest with me — I can take it.