Paste a Unix timestamp to see it as a date in UTC, in your local time zone and in ISO 8601 format, or go the other way and turn a date into a timestamp. Seconds and milliseconds are detected automatically, and the current timestamp ticks live at the top.
The number of seconds elapsed since 1 January 1970 at 00:00:00 UTC, ignoring leap seconds. Because it is a single integer in UTC, it sidesteps time zones and formatting entirely, which is why it is used everywhere in software.
A 10-digit number is seconds; 13 digits is milliseconds. JavaScript works in milliseconds while most other languages and databases use seconds, which is a very common source of dates landing in 1970 or in the year 55000.
A signed 32-bit timestamp overflows on 19 January 2038 and wraps to a negative number, putting the date in 1901. Modern systems use 64-bit timestamps, which do not overflow for another 292 billion years, but legacy systems and embedded devices remain a concern.