ISO 8601 is the internationally accepted standard for describing dates and times. It eliminates ambiguity across countries that format dates as MM/DD/YYYY or DD/MM/YYYY.
Standard ISO 8601 Structure
YYYY-MM-DDTHH:mm:ss.sssZ
- YYYY: 4-digit Year (e.g. 2026)
- MM: 2-digit Month (01 to 12)
- DD: 2-digit Day (01 to 31)
- T: Separator denoting the start of time segment
- HH:mm:ss: Hours, Minutes, Seconds
- Z: Zero UTC offset (or specified offset like +05:30)
Why ISO 8601 Matters for APIs
ISO 8601 strings are lexicographically sortable. Ordering ISO 8601 strings alphabetically automatically sorts them in chronological order!