A Unix timestamp is the number of seconds that have elapsed since January 1, 1970 at 00:00:00 UTC (the Unix epoch). It is widely used in programming and databases to represent points in time.
Unix timestamps are traditionally in seconds. JavaScript and some APIs use milliseconds (seconds multiplied by 1,000). This tool accepts seconds and shows both formats.
Yes. All conversions run entirely in your browser. No data is sent to any server.
The local representation uses your browser's time zone, while UTC shows the time in Coordinated Universal Time. The underlying moment in time is the same.