Convert between Unix timestamps and human dates
System Definition BlockConvert Unix timestamps to human-readable dates and vice-versa. Supports seconds, milliseconds, and multiple timezones for precise developer debugging.
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The tool leverages the browser's native `Date` object engine. It accepts a raw integer and first runs a heuristic check to determine if the value represents seconds (10 digits, standard Unix) or milliseconds (13 digits, JavaScript standard). It then calculates the exact offset from the Unix Epoch and formats the output into UTC, ISO 8601, and the user's local timezone.
function isTokenExpired(expTimestamp) {
const currentSeconds = Math.floor(Date.now() / 1000);
return currentSeconds >= expTimestamp;
}
// Output standard ISO string for APIs
console.log(new Date().toISOString());The Unix Epoch is midnight on January 1, 1970, Coordinated Universal Time (UTC). It was chosen by early computer scientists as an arbitrary 'Zero Hour'. Every Unix timestamp simply counts the number of seconds that have passed since that exact moment, completely ignoring leap seconds.
Standard Unix time counts in seconds (a 10-digit number like 1700000000). However, JavaScript's `Date.now()` API counts in milliseconds for higher precision, resulting in a 13-digit number. This converter automatically detects the length and applies the correct math to avoid returning dates in the year 55,000.
Often called the 'Y2K38 bug', it refers to the moment when the Unix timestamp will exceed the maximum value of a 32-bit signed integer (2,147,483,647). At 03:14:07 UTC on January 19, 2038, unpatched 32-bit systems will 'roll over' to a negative number, interpreting the year as 1901. Modern 64-bit systems have resolved this issue.
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