What a Unix timestamp is
A Unix timestamp (also called epoch time) is the number of seconds that have elapsed since 1970-01-01 00:00:00 UTC, not counting leap seconds. It's a compact, time-zone-free way to store an instant, which is why logs, databases and APIs use it everywhere.
Seconds vs milliseconds
Unix time is classically in seconds (10 digits for current dates). Many systems — JavaScript's Date.now(), and some Firebase/Java APIs — use milliseconds (13 digits). This tool auto-detects: 13-digit inputs are treated as milliseconds, 10-digit as seconds.
FAQ
Why is my date off by hours?
Timestamps are UTC-based. This tool shows both your local time and UTC so you can tell them apart. An offset usually means you were comparing local vs UTC.
Is anything sent to a server?
No. All conversion happens in your browser.
What's the year-2038 problem?
Systems storing Unix time in a signed 32-bit integer overflow on 19 January 2038. Modern platforms use 64-bit, which pushes the limit far into the future.