How building a simple "middleman" tool for Kindle users turned into a universal learning platform

Hey !

I wanted to share how my side project accidentally evolved from a simple file utility into a full scale learning platform.

The Problem

It started because I make KAnki, which is essentially Anki for Kindles. It lets people study flashcards offline on jailbroken Kindle devices. However, the workflow to get files onto the device was incredibly clunky. People wanted an easier way to get their standard Anki decks formatted, edited, and successfully exported into their Kindle configurations. They needed a middleman.

So, I built a web utility to bridge that gap. The original goal was straightforward: import an Anki .apkg file, edit it cleanly in a web UI, and export a flawless KAnki configuration.

The Pivot

But once people started using it, they didn't just want to pass files through, they wanted to stay.

I started expanding features for language learning, but quickly realized the mechanics of memory are universal. If the UI could handle complex languages, it could handle anything.

That middleman utility grew into Üben (uben.online), a full platform powered by the advanced FSRS spacing algorithm. It still handles the original KAnki Kindle workflow perfectly, but now users can track analytics, earn badges, and study any subject from coding to history directly on the web.

The Tech

To scale from a basic tool to a database heavy platform, I recently migrated the backend completely to Supabase (Postgres and Auth) and kept the frontend fast with React.

Because of the database overhaul, I had to make the tough call to reset early test accounts and ask users to re import their decks. A scary move, but the speed gains made it 100% worth it.

Üben is currently free, bootstrapped, and in a live phase.

If you use a Kindle or study with flashcards, I'd love your brutal feedback! Check it out at uben.online.