ISO 8601 is the international standard for writing dates and times, and it has more forms than most people realise. Pick a date and time and this formatter produces the extended form, the basic form without separators, the week date, the ordinal date, RFC 2822 and the Unix timestamp — all copyable.
Why big-endian ordering wins
Writing the year first, then month, then day, means a plain string sort is also a chronological sort. That single property is why filenames, log lines and database columns should use it. The full explanation is in ISO 8601 explained.
Week dates and ordinal dates
The same standard defines 2026-W31-3 (year, ISO week, weekday) and 2026-212 (year and day of year). Week dates matter in payroll and manufacturing; ordinal dates appear in astronomy and aviation. Their rules are covered in ISO week numbers.