Turn a Unix timestamp into ISO, UTC and your own time zone at once, or paste a date and read the epoch back. Seconds and milliseconds both.
Unix time is defined in seconds, and most backends store it that way, but JavaScript's Date.now returns milliseconds. A ten digit number is almost always seconds and a thirteen digit one milliseconds; the switch here decides how a plain number is read.
Yes. Anything the browser can parse works in the same field, so an ISO string such as 2026-08-18T09:30:00Z gives you the epoch back, along with the UTC and local readings.
Your own, as the browser reports it. The ISO and UTC rows never move, which is what makes them the pair to quote in a bug report: a timestamp read in two time zones is how most scheduling bugs start.
A signed 32-bit timestamp runs out on 19 January 2038, and rolls over to 1901. Anything still storing seconds in an int is affected, which is mostly old C, embedded systems and a few database columns. A 64-bit integer fixes it, and most modern stacks already use one.