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I Built a Habit Tracker in 30 Minutes with Claude Opus 4.5

My daily fitness habits are lackluster compared to where I was at the beginning of this year. When you’re out of practice, the hardest thing to do is get started again. To that end, I’ve been attempting to build some momentum by setting some tangible fitness goals that are laughably easy to accomplish. So much so that it would be silly not to do them. All I set myself up to do is 5 push-ups, 5 sit-ups, and 5 air squats. The idea is if I can string enough of these together, I’ll find myself back into a rhythm and I can increase the intensity over time.

I wanted to build a tracker for myself to stay accountable, try out Claude Opus 4.5 in Cursor, and practice my shipping skills - so I gave myself 30 minutes to build and deploy it.

My tech stack was Next.js, Clerk, and Convex - I set these up by hand first since doing the initial config takes guesswork away from the agent. After the setup I fired up Cursor with Claude Opus 4.5, laid out my prompt and let the agent go to work.

I used planning mode because it tends to yield better one-shot results. I was surprised how concise, but well articulated the plan was. Other models I’ve used create massive plans full of redundant details, but Opus was concise and readable.

A shocking move since I last used Cursor was that the agent opened up a browser window after it finished to check its work. It ended up catching a runtime error and fixing it which I would have previously needed to hand check and ask it to fix. That saved me a decent amount of time and was genuinely impressive.

It cost $0.56 total (Opus currently billed at Sonnet 4.5 rates on Cursor), basically one-shot the whole app, and I deployed to Vercel within my 30-minute window.

What I learned:

  • Models have come a long way and can one-shot simple apps (and for cheap).
  • It’s easier than ever to go from idea to shipping something.
  • Opus 4.5 is not as quick as my previous favorite model (Cursor’s Composer model), but the time to effectiveness trade-off seems very worth it.
  • The agent’s ability to open a browser and run its own testing is a game changer.

I’ve been using my tracker daily. Now I’m wondering what else I can ship in 30 minutes.