I built this because I was sick of doing timezone math by hand every time I had to schedule something with someone in another country. I kept opening tabs, converting “3pm PT” to five different cities, then hand-typing the result into Slack. Small annoyance, but it happened constantly. So now there’s Worldline: drag one slider, see everyone’s local time update live and color-coded, hit “find a good time” to get a few suggested windows, and copy a ready-made message instead of typing it out again.

I wrote the actual logic myself: the timezone conversion, the slider, the scoring for what counts as a “good” time. But I leaned on Claude a fair amount along the way. It helped me debug a nasty DST-related bug where everyone’s time except mine was off by an hour depending on the date; I could tell something was wrong but Claude spotted that I was building the reference date in the wrong spot relative to the timezone conversion. It also did most of the heavy lifting on styling, left alone this would’ve been black text on white with default buttons, so the color palette, spacing, and the slider actually looking like a slider is basically all Claude’s doing on the CSS side. I’m sorry I don’t know how to style ok? 🫠

It’s rough in places, the timezone dropdown is a shortlist of ~30 common zones, not the full IANA list, and “good time” just means 9–6 for everyone with no real concept of actual work schedules. But it does the one thing I built it to do: drag, copy, paste, done. v1.0, shipped.