Paste a Unix timestamp (epoch seconds or milliseconds) to see the equivalent UTC and local date, or paste a date string to get its Unix timestamp. Auto-detects which you entered. Pure in-browser.
By length: a plain integer longer than 11 digits is read as milliseconds and everything else as seconds, so 1717000000 is seconds while 1717000000000 is milliseconds. The "Interpreted as" row confirms which one was used.
Your own device's timezone, as reported by your browser — the site does not ask for or guess a location. The UTC, ISO 8601 and Unix values are timezone-independent, so use those when sharing a time with someone else.
No. Conversion is done locally in your browser and nothing you enter is uploaded. After the page loads it keeps working offline, which also means the result depends on your device clock, not a server time source.