cloud / systems
For months, I looked for an app to record my progress in dumbbell training. Some were expensive. Others had too many ads. And some simply did not do what I was looking for. Eventually, I picked up a notebook.
The notebook did the job
I started recording my training progression by hand. Exercise, weight, repetitions: the information I wanted to keep was straightforward. A notebook did not interrupt me with advertising or ask me to adapt to somebody else’s idea of a training app.
But as the entries accumulated, I wanted more than a record of individual sessions. I wanted to see how my training developed over time. The history was there, spread across handwritten pages.
Why not build it myself?
That was the turning point. Instead of continuing to search for the right app, I asked myself: why not build exactly what I need?
For the start, I already had my OpenAI subscription, my MacBook and Codex. I could describe what mattered to me and use Codex to help turn those requirements into an app. I called it Kraftwerk.
The starting point was a small, practical question: what do I want to enter after an exercise, and what do I want to understand when I look back?
My training history was already on paper
Building an app did not mean I wanted to start again from zero. Months of handwritten entries were part of the story.
I photographed my existing notes, imported the photos and had Codex read the training data from them. The notebook became the starting point for the digital history rather than an archive I had to leave behind.
For me, that was one of the most useful parts of the project: the work I had already put into documenting my training could carry forward into the new app.
Enter the session. See the progression.
In Kraftwerk, I select an exercise and enter weights and repetitions for each set. Saved sessions become a history I can revisit, with charts showing training volume and development over time.
The screenshots below show the original entry interface and a progress view with my recorded training data. The app itself is private; the public Kraftwerk page on this website presents selected results as a read-only view.
From logging a set to seeing the trend
A personal problem became a software project
I had been looking for a product that fitted my routine. In the end, my own routine supplied the requirements for building one.
That is what I like about this project. It connects something I do away from the laptop with the pleasure of building software. Codex helped me turn an idea into something I can use, including the handwritten history that came before it.
The notebook was a good beginning. Kraftwerk is the next chapter.
This article tells my personal development story. Codex supported development and preparation of this article; the experience and project are my own.