I found a 23-second API response in my side project

I built AlmsTins, a crypto portfolio and tax tracking app, and finally load tested it with k6.

The results were humbling.

My diagnostics endpoint came back at 23.6 seconds on the first hit. Needs-attention was 3.2s, portfolio was 2.8s, and net worth was 1.8s.

The issue was not some mysterious infrastructure problem. I simply had almost no caching.

I added a three-layer cache:

After that, diagnostics dropped from 23,600ms to 441ms p95. The other endpoints all landed around 440–520ms.

The biggest lesson: if an app “works” locally, that does not mean it is ready for real users.

Load testing took about 20 minutes to write and exposed one of the biggest user-experience problems in my app.

For those of you building side projects: when did you first load test your app, and what did it reveal?