A Unix timestamp is the number of seconds (or milliseconds) that have elapsed since 1 January 1970 at 00:00:00 UTC — a fixed point in time known as the Unix epoch. It's used by virtually every programming language, database, and operating system to store dates as simple integers, which makes arithmetic easy and avoids timezone ambiguity. This tool converts in both directions, shows the current timestamp ticking live, and handles the full range from negative timestamps (pre-1970 dates) up to dates far beyond the year 2038 — which is only a problem for 32-bit systems, not for JavaScript or most modern software.