The timestamp tool covers four jobs in one page: a live Unix clock, timestamp-to-date conversion, date-to-timestamp conversion and a fixed multi-time-zone readout. Auto mode judges seconds, milliseconds or microseconds from the magnitude of the number and converts everything into JavaScript milliseconds; a date you type in is interpreted in the browser's local time zone.

1. 01Read the current seconds or milliseconds value and pause the live refresh if you want to copy a value that is not moving.
2. 02Enter a timestamp and choose Auto, Seconds, Milliseconds or Microseconds to see the local date, the UTC ISO string and the relative time.
3. 03Pick a local date and time with datetime-local to work back to Unix seconds and milliseconds.
4. 04Compare the same instant as shown locally, in UTC and in New York, London and Tokyo.

• The auto-detection thresholds are fixed: below 1e11 seconds, below 1e14 milliseconds, everything else microseconds; unusual historical or far-future values near a boundary should be given an explicit unit.
• Commas, whitespace and underscores are stripped from the input, and negative numbers and decimals are accepted.
• A converted value whose absolute millisecond count exceeds 8.64e15 is rejected, which is the limit of JavaScript's Date.
• datetime-local has no time zone field, so it is read in the current browser's local zone; the ISO output is then converted to UTC.
• The multi-zone panel uses the browser's Intl.DateTimeFormat and shows “not supported” for an IANA time zone the browser does not carry.

Time values are calculated and formatted locally in the browser and are never sent to a time service.