The idea of the app: With the fewest clicks possible, you can log: who, what and how much. Of anything actually but I used it for tracking fever and medicine intakes. The entries get timestamped and it shows you how long ago each entry was. You can filter by who and what. And that list, you can export or even create a PDF (more about that later). No account, installation or anything else needed.

Backstory:

When my kids were small they were often sick, sometimes both at once, and I lost track of which medicine I'd given to whom and who had how high a fever. During the day I could just about manage. At night, hopeless.

So I built a small phone app for myself, to log their temperature and what kind of medication I gave them. It was a local-only app (data stored in localStorage) and I used it for years. Then, my phone got damaged during a battery replacement and the data was gone (yay, local-only). It's not that I needed the data but sometimes, I felt nostalgic when scrolling through the old entries and started to think back to when my kids were smaller. It became a small diary of my kids (albeit only for their illness history haha but still). For example: Remember January 2020, when everyone was sick? I wonder what that was...

Fast-forward to this week: I rebuilt it (the original was Vue 2; I used Claude for the rewrite) and kept it local-only, but added import and export so I wouldn't lose the data again.

Technical background:

Everything lives in localStorage. No account, no backend, no analytics, no sync. It's also dark-themed by default, since I was often giving my kids some medicine at 3am and I didn't want to get blinded by my smartphone.

Lessons learned:

- Safari and the Home Screen app don't share storage. You enter data in Safari, add the app to your Home Screen, open it: empty. So there's a "copy my log" button, and the installed app offers to paste it on first launch. No idea how it works on Android since I don't have an Android phone to test. Sorry.

- Safari can delete localStorage after 7 days without a visit. Hence JSON/CSV export. Home Screen apps are exempt from this, so your data should be safe there, but I'm not 100% sure.

- window.print() does nothing in an installed PWA on iOS. So the app generates a PDF (a small custom generator instead of pulling in jsPDF, which is about 270 KB) and opens it in the share sheet, and you can print from there. Or you just show the doctor your phone.

Nothing you enter ever leaves your phone. It does check if there is an update of the PWA but that's about it. You can check it in the Network tab yourself.

If you've got curl, you can do something like this:

  curl -sI https://sesku.app | grep -i content-security

and then you'll see the CSP:

  content-security-policy: default-src 'self'; script-src 
  'self'; style-src 'self' 'unsafe-inline'; img-src 'self'; font-src 'self'; connect-src 'self'; manifest-src 'self'; worker-src 'self'; object-src 'none'; base-uri 'none'; form-action 'none'; frame-ancestors 'none'

connect-src 'self' means it can only talk to sesku.app itself, which only serves static files.

When you go to https://sesku.app and you see the demo animation, I used "fever" and it shows Celsius instead of Fahrenheit. So if you're European, and you see 39.6 on the thermometer, you'll be shocked. If you're American and the thermometer shows 39.6 you might be shocked as well...

So, happy to hear any feedback!

And for any Android users: Do you see the same entries when entered on sesku.app in the browser and also when installed as PWA?