Unix timestamp converter — offline

Epoch timestamps turn up everywhere a human has to debug something: log lines, JWT exp claims, database columns, API responses, cache headers. They are unreadable at a glance by design, and the numbers usually arrive attached to context — production log excerpts, customer records — that has no business being pasted into a random website.

Conversion here is plain date arithmetic running in your browser. Nothing about what you convert is transmitted or recorded; the site has no backend, and a Content-Security-Policy blocks third-party requests.

The seconds-versus-milliseconds confusion is the most common timestamp bug there is. Unix time is defined in seconds, but JavaScript's Date.now() returns milliseconds, so values from the two worlds differ by a factor of 1000 — and a millisecond value read as seconds lands roughly fifty thousand years in the future, while a seconds value read as milliseconds lands in January 1970.

Values of 13 or more digits are treated as milliseconds and shorter ones as seconds, and the interpretation is always displayed rather than silently assumed. If the resulting date looks absurd, the units are almost certainly the reason.

You can paste in either direction: a raw timestamp, or anything JavaScript can parse as a date such as ISO 8601 (2026-07-19T12:00:00Z).

Every conversion is shown three ways at once, because each answers a different question. UTC is what your servers and logs are almost certainly using. Local time is what the person reading the ticket experienced. Relative time — "3 days ago", "in 58 minutes" — is what actually tells you whether something is stale, expiring, or already broken.

Timezone confusion is the second great source of timestamp bugs, especially around daylight saving transitions, where a local wall-clock time can be ambiguous or simply not exist. Storing and comparing in UTC and converting only for display avoids essentially all of it.

Related and also local: the JWT decoder, which renders exp, iat, and nbf as readable dates automatically, and the cron parser for schedules rather than instants.