A Unix timestamp is the number of seconds (or milliseconds) since January 1, 1970 UTC: unambiguous for a machine, unreadable for a person. This converts a timestamp into a readable date in both your local timezone and UTC, and back the other way, auto-detecting whether a pasted number is in seconds or milliseconds.
When you'd use this
Reading a timestamp out of an API response, a log file, or a database row without doing the arithmetic in your head. Or the reverse trip, turning a specific date and time into the epoch value a script or API expects.
Common errors
A date that's off by exactly one time zone's offset, often by several hours, usually means the local-time and UTC readings of the input got crossed. Check which one the original source used.
A timestamp landing decades away in either direction almost always means seconds and milliseconds got confused. 1700000000 is a valid date in seconds (late 2023), and an implausibly early one if read as milliseconds.
Frequently asked questions
How does this tell seconds and milliseconds apart automatically?
By digit count. A seconds-based Unix timestamp for any date in the last ~50 years has 10 digits, while the same moment expressed in milliseconds has 13. That gap is wide enough to detect reliably without you having to say which unit you're pasting.
Why does the same timestamp show two different times?
One is your local time, taken from your device's timezone setting, and the other is UTC. Same instant, displayed two ways. APIs and logs commonly store UTC to sidestep timezone ambiguity, so both readings are shown here.
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