A Unix timestamp (or epoch time) counts the number of seconds — or milliseconds — that have elapsed since January 1, 1970 00:00:00 UTC. It's how most systems and databases store points in time internally, since it's a single unambiguous number rather than a locale-dependent string.
This tool converts a timestamp to a human-readable date in your local timezone, in UTC, and in ISO 8601 format, and works the other way around too: pick a date and time and get back its Unix timestamp in seconds or milliseconds.
What's the difference between seconds and milliseconds epoch?
Unix time is traditionally counted in seconds since 1970-01-01 UTC; many JavaScript APIs (like Date.now()) use milliseconds instead — mixing the two up produces a date wildly off (usually in 1970 or thousands of years in the future).
Does the converted date use my local timezone?
The tool shows both UTC and your browser's local timezone, since a raw Unix timestamp has no timezone of its own — it's always an offset from UTC.
What's the year 2038 problem?
Systems that store Unix time as a signed 32-bit integer will overflow on 2038-01-19; this tool uses JavaScript's 64-bit-safe number handling, so it isn't affected, but many older C-based systems are.