Developer
Unix timestamp to date and back
Convert a Unix epoch timestamp (seconds or milliseconds since 1970-01-01 UTC) to a human-readable date, and vice versa.
About this conversion
JavaScript and most JSON APIs use milliseconds since 1970-01-01 UTC. Unix command-line tools and many databases use seconds. If your number has 10 digits it is almost certainly seconds; 13 digits, milliseconds.