The 1.4 Million Line Delete

The numbers speak for themselves:

• -1,392,860 lines deleted
• +334,224 new lines written
• 181 commits
• 3 weeks of work

I just finished a complete backend rewrite for Kvalty.cz. Threw out Directus and replaced it with a custom solution.

Why?

I won’t lie — it was a ride. For a single person, this would normally be a nightmare lasting at least half a year, with a serious risk of nuking the entire production. But I build all of Kvalty using vibe engineering methodology, so instead of fearing the migration, I just grabbed Claude Code and we went for it.

The Reality

It wasn’t “first try, perfect result.” A few times, AI and I seriously misunderstood each other, and some of the more complex parts needed iteration to actually work in production. No magic autopilot happened.

It worked like extremely intensive pair programming. I played the architect, set the guardrails, and Claude did the raw heavy lifting. I had to do honest code reviews, push back, and hold the direction when it started coming up with nonsense.

The Result

Worth the nerves. The backend is now much higher quality, the code is clean, and most importantly — it’s a joy to work with now.

Claude Code just had its birthday — one year — and I’ve come an enormous distance with it during that time. I created all of Kvalty with it — a project that’s already huge and growing, but we’re really still at the beginning.

This rewrite was the biggest challenge so far, one I definitely couldn’t have pulled off without that year of experience and mutual calibration.

The Lesson

AI is an incredibly powerful tool. But you have to know how to work with it.

There’s no shortcut around understanding your own system. The rewrite worked because I knew what the old backend did wrong, what the new one needed to do right, and I could verify every decision Claude made. Without that context, the same rewrite would have been a disaster.