A live board of any cities you care about: local time, weekday, date and real UTC offset with daylight saving already applied. Add up to twelve, drag the hour slider to see what one moment looks like everywhere at once, and spot instantly who is asleep. Runs on your device's clock — no server, no tracking.
Each city is an IANA time-zone name (the same identifiers your operating system uses). Times are formatted with
the browser's own Intl.DateTimeFormat in that zone, so summer time is applied from your system's
time-zone database rather than a hardcoded table — nothing here goes stale when a country changes its clocks.
The UTC offset is measured, not assumed: the same instant is rendered in UTC and in the target zone, the difference is taken, and the result is rounded to the minute, which is why half-hour zones such as Kolkata (+05:30) and 45-minute zones such as Kathmandu (+05:45) show correctly.
The scrub slider takes today's date in your zone at the chosen hour and re-renders every city for that single moment, so you can see which side of midnight a call lands on. Your board is remembered in this browser's local storage; no network request is ever made.