How does it know seconds from milliseconds?

In Auto mode, values of 1,000,000,000,000 or more are treated as milliseconds and smaller values as seconds. The assumed unit is always displayed and can be overridden.

Why do UTC and local time differ?

A Unix timestamp is one instant in UTC. The local line renders the same instant in your device timezone, so the clock reading differs by your UTC offset. Both lines describe the same moment.

Is anything uploaded?

No. All conversions run in your browser tab. Nothing is uploaded, stored or shared.

Unix Timestamp Converter — Epoch naar datum, UTC & lokaal, gratis

Gratis Unix-converter. Live epoch-klok, seconde/millisecondedetectie met getoonde aanname, UTC en lokale tijd naast elkaar, kopieerbare ISO 8601 en datum naar timestamp. Volledig lokaal, geen upload.