What this tool answers
Logs, tokens, cache headers, and database rows all carry Unix time, and the number is hard to read without converting it. This page converts in both directions: paste a timestamp to see local time, UTC, and ISO 8601, or pick a date to get seconds and milliseconds.
How to use it
Paste a number into the timestamp field. Values with 13 digits or more are treated as milliseconds; shorter values are treated as seconds up to a sane cutoff, and the detected unit is shown next to the result. Press Now to load the current time. The results update as you type, so you can paste a log value and read it immediately.
For the reverse direction, choose a date and time in the date field and press Convert date. The output gives both Date.getTime() / 1000 and the millisecond value, which is the pair most APIs disagree about. A relative line ("3 hours ago", "in 2 days") helps when you are scanning a list of events.
What it does not do
It does not know which time zone the timestamp was recorded in, because a Unix timestamp does not carry one. It is an instant, and this page renders that instant in your browser's local zone and in UTC. If a log says 09:00 but the server was in another zone, the timestamp is still correct; your reading of the wall-clock time is what changes.
It does not parse every date format ever written. The date field uses the browser's native date-time control, which accepts a calendar value, not a free-form sentence. It does not convert time zones for a scheduled future event; use a calendar tool for that.
When a conversion looks wrong
Check the unit first. A seconds value interpreted as milliseconds lands in January 1970; a milliseconds value interpreted as seconds lands tens of thousands of years in the future. Check daylight saving next: the same instant has different local wall-clock readings across the year. Finally, check whether the system that produced the number used seconds since the epoch or a different epoch. This tool assumes the standard Unix epoch, 1 January 1970 UTC.