What is a Unix timestamp?
A Unix timestamp counts time from 1 January 1970 at 00:00:00 UTC. It is commonly used in logs, APIs and databases because a numeric value is easy to store and compare. Negative values can describe dates before that starting point.
Are timestamps in seconds or milliseconds?
Both conventions appear in software. JavaScript dates commonly use milliseconds, while many APIs use seconds. Choose the input unit explicitly. A timestamp of 1,700,000,000 seconds is a different date from 1,700,000,000 milliseconds; extra digits are not simply a formatting preference.
Does a timestamp have a time zone?
The same instant can be displayed in different time zones. This tool shows both UTC and the time zone reported by your device. When converting a typed date, choose whether that date means UTC or your device’s local time.
What happens when clocks change?
Some local times do not exist during the spring change, while others occur twice in autumn. The converter rejects local times that roll into a different time. Use UTC when you need an unambiguous comparison; an ambiguous local autumn time follows the browser’s interpretation.
Read MDN’s JavaScript Date reference. For a support request, the main checker also reports your device’s time zone.