ISO 8601 Date Validator
Validate ISO 8601 / RFC 3339 date strings in bulk. Catch malformed formats, illegal leap days, out-of-range components, and missing offsets. 100% browser-based, no uploads.
ISO 8601 vs RFC 3339
ISO 8601 is the broad international standard for date and time representation. It allows many forms: calendar dates, week dates, ordinal dates, durations, and intervals.
RFC 3339 is a strict subset of ISO 8601 designed for internet protocols. It requires a full date-time with an explicit timezone offset (Z or ±hh:mm). When a spec says "ISO 8601," it almost always means the RFC 3339 subset.
This validator checks both: it flags RFC 3339 compliance separately from general ISO 8601 validity.
Supported Formats
Calendar dateMost common
2026-05-26Date + time, UTCRFC 3339
2026-05-26T14:30:00ZDate + time, offsetRFC 3339
2026-05-26T14:30:00+05:30Date + time, no zoneLocal time
2026-05-26T14:30:00Week dateISO 8601 only
2026-W22-2Ordinal dateISO 8601 only
2026-146DurationISO 8601 only
P3Y6M4DT12H30M5SIntervalISO 8601 only
2026-01-01/2026-12-31Common Use Cases
- •Validating API payload timestamps before processing
- •Auditing timestamps in JSON or NDJSON logs
- •Cleaning CSV columns of mixed date formats before ETL
- •Pre-flight checking webhook payload timestamps
- •Verifying OpenAPI/Swagger date-time fields