What is a Unix timestamp?
A Unix timestamp is the number of seconds elapsed since 00:00:00 UTC on 1 January 1970 (the "epoch"). It is a timezone-independent way to store an exact moment in time.
Seconds or milliseconds — which is it?
Unix time is in seconds; JavaScript and many APIs use milliseconds (1000× larger). This tool auto-detects: 13-digit values are treated as milliseconds, 10-digit as seconds.
Why does the local time differ from UTC?
The same instant is shown in two zones: your browser's local timezone and Coordinated Universal Time (UTC). Servers usually log in UTC, so compare against that.
What is the year 2038 problem?
A signed 32-bit timestamp overflows on 19 January 2038. Modern 64-bit systems and languages avoid this, but legacy systems storing time in a 32-bit integer can still be affected.
