Auto reads the magnitude: 1e11 or above is milliseconds. Set the unit explicitly if that guess is not what you meant.
Nothing here yet
Convert epoch seconds or milliseconds to a date and back. Local time and UTC are shown together, ISO 8601 is given both with an offset and in UTC, and the current Unix time is always on screen.
Questions
Where does "this device" come from?
The time zone the browser reports, which follows your computer or phone settings. The zone name (Asia/Tokyo and the like) and the offset are shown at the top so you can confirm it is the setting you expected. To compare against a server, use the UTC row — it does not depend on this device at all.
Does it handle daylight saving?
Yes. The offset is taken from the instant in question, so it switches by itself between summer and winter. Note that at a transition one hour either does not exist or happens twice; a time inside the missing hour is nudged to a nearby instant by the browser’s own rules, and a time inside the repeated hour is read as one of its two possible instants. Write the offset into the text (+09:00) or enter it as UTC when the difference matters.
Negative values and fractions?
Negative values are dates before 1970 and work normally. A fractional number of seconds (1786500000.5) is accepted and converted to milliseconds; the displayed clock time is whole seconds, so read the milliseconds row for anything finer. A number far outside the representable span is reported as out of range rather than printed as nonsense.
Which date formats are accepted?
2026-08-15, 2026-08-15 12:34:56, 2026/8/15 12:34, 2026-08-15T12:34:56Z and 2026-08-15T12:34:56+09:00. When the text carries a Z or an offset, that takes precedence over the zone switch. With the time omitted, midnight is assumed. A date that does not exist — 30 February — is rejected rather than rolled forward to 2 March, because saying the input is wrong is safer than silently changing it.
Is anything uploaded?
No. Every calculation happens in the page, so timestamps out of logs you cannot share are fine to paste here. The clock at the top comes from your own device, not from a time server.