Is this timestamp converter free to use?

Yes. Converting timestamps is completely free with no limits or sign-up required.

What is a Unix timestamp?

A Unix timestamp is the number of seconds (or milliseconds) that have elapsed since January 1, 1970, 00:00:00 UTC, known as the Unix epoch.

Is my data sent to a server?

No. All conversions happen locally in your browser using JavaScript's Date object — nothing is uploaded or stored.

Should I store timestamps in seconds or milliseconds?

Unix time is traditionally measured in seconds, and most databases and APIs (like PostgreSQL's epoch or Python's time.time()) use seconds. JavaScript's Date.now() uses milliseconds instead. Pick whichever your stack already uses consistently, and this tool auto-detects which one you've pasted based on its length.

Why did my timestamp turn into a date in 1970 or far in the future?

The unit was probably misread. Auto mode treats up to 10 digits as seconds and longer values as milliseconds, so microsecond (16-digit) or nanosecond (19-digit) timestamps from some logs and databases come out wrong. Divide them by 1,000 or 1,000,000 first, or force the unit with the Seconds / Milliseconds buttons.

Why does the same timestamp show a different date for my colleague?

A Unix timestamp represents one exact moment in time, but 'local time' depends on the viewer's timezone. If you're in New York and your colleague is in Tokyo, the same timestamp can fall on different calendar dates for each of you. Always compare the UTC value if you need a timezone-independent reference.