ISO 8601 Validator
Paste any ISO 8601 string — date, time, datetime, duration (P1DT2H30M),
interval (start/end) or repeating interval (R5/…) — and see it parsed
component by component. RFC 3339 (the stricter internet profile) is checked separately, because
“valid ISO 8601” and “valid RFC 3339” are not the same thing.
Examples:
ISO 8601 vs RFC 3339, in one table
| Feature | ISO 8601 | RFC 3339 |
|---|---|---|
Basic format 20260612T103000Z | valid | invalid — separators required |
Week dates 2026-W24-5, ordinal 2026-163 | valid | invalid |
| Date without time, time without date | valid | invalid — full date-time only |
| Missing UTC offset | valid (local time) | invalid — offset required |
Offset +0300 / +03 | valid | invalid — must be +03:00 |
Space instead of T | invalid (common in SQL) | invalid, but tolerated by many parsers |
Comma as decimal mark 10:30:05,5 | valid (even preferred) | invalid — dot only |
Lowercase t / z | invalid | valid |
-00:00 (offset unknown) | invalid | valid — means “UTC, local zone unknown” |
Durations P1DT2H, intervals, repeats | valid | appendix only, not in the grammar |