2026-10-19 · 8 min read
- time
- unix
- iso8601
The timestamp page converts two independent fields. The Unix field is seconds: the number is multiplied by 1000 and shown as an ISO instant. The ISO field is parsed by itself, and the seconds under it are the floor of that instant divided by 1000. Typing in one field does not rewrite the other. The Now button is the control that writes both, from the current clock.
Label the unit in the note before you paste. Ten digits are seconds. Thirteen digits are milliseconds and will be wrong in the Unix box, because the box multiplies again.
An empty Unix box is the epoch
The Unix value is passed to the number parser. An empty string becomes 0, and 0 is finite, so the line under the box is 1970-01-01T00:00:00.000Z. That is the same result as typing 0. It is not an unset field and it is not Invalid.
Spaces around a number are ignored by that parser. A padded 10 is ten seconds past the epoch. 1.9 seconds keeps the 900 milliseconds in the ISO line. 1e9 is one billion seconds, and the instant is 2001-09-09T01:46:40.000Z. Scientific notation is accepted on this field. abc and Infinity are Invalid. A 13-digit finite number is not Invalid. 1700000000000 prints a year of 55840, +055840-11-08T22:13:20.000Z. The seconds form of that instant is 1700000000, 2023-11-14T22:13:20.000Z.
- Count digits before you blame a timezone.
- Treat a blank Unix box as 1970.
- Divide a millisecond log by 1000 before you paste it.
- Keep the fractional second if the Unix text had one.
Floor the ISO side, and write the zone
2026-10-19T00:00:00.900Z is an instant with 900 milliseconds. The seconds field under it is 1792368000. The floor discards the fraction. It does not round to 1792368001. If you need the milliseconds, they are in the ISO text, not in that integer.
A date-only value such as 2026-10-19 is UTC midnight, the same 1792368000. A date-time with no offset is local. On 19 October 2026 in America/New_York, where the offset is four hours, 2026-10-19T00:00:00 is 2026-10-19T04:00:00.000Z. The Z form and the bare form are different instants. Put the offset in the string you copy.
Do not mix this clock with the cron clock
The cron tool previews the next five runs of a five-field expression in a timezone you type, and it starts from the current time. It does not interpret a Unix field, and it does not read an offset out of an ISO string. A job that should fire at a UTC second needs both: the expression in the cron tool, and the resulting ISO checked in the timestamp tool.
Copy Unix copies the Unix box text. Copy ISO copies the ISO box text. Neither copies the converted line under the field. If the boxes have drifted because you edited only one, the copy is the stale box, not the conversion.
Put the unit next to the claim
JWT exp and iat values are NumericDate seconds. A JSON payload that stores milliseconds will look expired, or far future, when a verifier treats them as seconds. Format the JSON, read the number, and convert it in the Unix box only after you have counted digits.
Use the timestamp tool for the conversion, the JSON formatter for the claim, the cron tool for the schedule, and diff for the original digits against the ISO line you are about to quote. The note should include the unit, the zone, and whether the Unix box was empty.