Does it support seconds and milliseconds?

Yes. Values are detected automatically — large numbers are treated as milliseconds.

Can I convert a date back to a timestamp?

Yes. Enter a date string and you'll get the Unix seconds and milliseconds.

No. Conversion runs entirely on your device.

Convert Unix timestamps (seconds or milliseconds) to ISO, UTC and local dates — and back. Runs entirely in your browser — no uploads.

Enter a Unix timestamp (seconds or milliseconds) or a date.

Convert between Unix timestamps and human-readable dates in both directions, with seconds and milliseconds support.