Unix timestamp conversion

A Unix timestamp counts the number of seconds that have elapsed since the Unix epoch — January 1, 1970, 00:00:00 UTC. It's timezone-agnostic by design: the number itself doesn't encode a timezone at all, and converting it to a readable date in a specific timezone is a separate display step performed by whatever's reading the timestamp, not something baked into the number.

The most common mistake is unit confusion. A timestamp in seconds for a recent date is a 10-digit number; the same moment in milliseconds is 13 digits; some systems (particularly databases and high-precision logging) use microseconds (16 digits) or nanoseconds (19 digits). Feeding a millisecond timestamp into a tool expecting seconds lands you somewhere around the year 46,000 rather than today — which is usually the first sign something's off.

There's also a real deadline behind epoch time: the classic 32-bit signed Unix timestamp overflows at 03:14:07 UTC on January 19, 2038 — the "Year 2038 problem." Most modern systems have already moved to 64-bit timestamps, which push that ceiling out for billions of years, but any code still storing epoch time in a 32-bit signed integer will wrap around and produce an invalid or negative date at that moment. Unixly and Epochly both handle the seconds/milliseconds/microseconds/nanoseconds detection automatically and convert in both directions instantly, without a network round-trip.