Current Unix Timestamp

Needing the exact current epoch value comes up constantly in ordinary development work: seeding a test fixture with a realistic creation timestamp, constructing an API request that expects a `timestamp` parameter reflecting the moment of the call, or checking whether a token's expiry value has actually passed by comparing it against right now. A ticking, continuously updating value removes the small but real risk of copying a timestamp that is already a few seconds stale by the time it gets pasted somewhere else — the number shown is always the actual current moment, not a snapshot from whenever the page happened to load.

Showing seconds and milliseconds side by side rather than picking one removes the need to know in advance which unit a particular API, database column or test fixture expects — JavaScript's own `Date.now()` returns milliseconds, while most Unix system calls and many APIs expect seconds, and copying the wrong one produces exactly the ten-versus-thirteen-digit mismatch that causes a timestamp to land in 1970 or the year 55000 instead of the intended moment.

Comparing a live, ticking timestamp against a value freshly returned by a system under test — a new database row's `created_at` value, a session token's `iat` claim — is a fast manual sanity check that the system is stamping current time correctly rather than an offset, cached, or stale value. If the two values do not land within a second or two of each other, something in the system being checked deserves a closer look.