Unix Timestamps Explained for Non-Developers

Early Unix systems needed a simple reference point. January 1, 1970 UTC became standard. Timestamps are usually seconds; JavaScript uses milliseconds (`Date.now()`), which trips people who divide by the wrong factor.

• JWT `exp` and `iat` claims
• Database `created_at` columns
• CDN and server access logs
• Webhook payloads and queue messages
• File metadata and backup catalogs

Unix time is always UTC. Display layers convert to local time for humans. Daylight saving changes affect labels, not the underlying integer. Scheduling "9 AM New York" still requires timezone-aware libraries—timestamps alone do not encode DST rules.

32-bit signed integers overflow around 19 January 2038. Modern systems use 64-bit time_t, but embedded devices and legacy MySQL `TIMESTAMP` types deserve audits. If you maintain long-lived IoT firmware, plan migrations early.

1. 1

   Copy the integer from logs

   Confirm seconds vs milliseconds.

2. 2

   Convert to ISO/local

   Compare with incident report times.

3. 3

   Generate now() for tests

   Seed fixtures with realistic values.

When support pastes a mysterious ten-digit number, the Timestamp Converter on XSular Tools flips between Unix seconds, ISO strings, and readable local time without opening a terminal.

`2025-05-31T14:30:00Z` is unambiguous in JSON APIs. Many teams store ISO strings in documents and integers in analytics warehouses. Know which format your current tool expects before bulk imports.