How it works
A number is parsed as a Unix timestamp — seconds or milliseconds since January 1, 1970 UTC, detected by its length — and converted to a JavaScript date. Anything else is handed to the browser’s own date parser, which understands ISO 8601 and most common written date formats.
Seconds vs. milliseconds
Unix timestamps were traditionally measured in seconds, which is what
date +%s and most server-side languages still use by default.
JavaScript’s own Date.now() uses milliseconds instead, so this tool
detects which one you have from the number of digits and labels the
result accordingly.
Reading the output
ISO 8601 and UTC are timezone-independent, so they mean the same thing everywhere. The “Local” row shows the same instant in your browser’s own timezone, and “Relative” describes roughly how far that moment is from right now.