ISO 8601 Timestamp Formatter
Generate ISO 8601 / RFC 3339 dates, Unix timestamps, and RFC 2822 email dates in real time. Live UTC clock, seven format cards with one-click copy, and a custom format builder. Everything runs client-side — no server round-trips.
Custom Format Builder
Configure the date order, time precision, timezone representation, and separator to generate a custom timestamp format. The preview updates live as you change options.
What Is ISO 8601? The Standard Timestamp Format
ISO 8601 is the international standard for date and time representation, published by the International Organization for Standardization. It defines an unambiguous format like 2026-07-27T14:30:00Z — year-month-day, then a T separator, then hours:minutes:seconds in 24-hour time, and optionally a timezone designator. RFC 3339 is the IETF profile of ISO 8601 used on the internet; the two are effectively interchangeable for most engineering purposes.
Why use ISO 8601 over other date formats?
ISO 8601 sorts chronologically when dates are compared as strings (lexicographic order equals temporal order). This property makes it the standard for log files, API payloads, database timestamps, and serialization. Formats like MM/DD/YYYY and DD/MM/YYYY are ambiguous across locales — 03/04/2026 is March 4th in the US but April 3rd in the UK. ISO 8601 eliminates that ambiguity entirely.
Related Timestamp Tools on jslet
If you need to convert between epoch timestamps and human-readable dates, try the Unix Timestamp Converter. This tool handles 32-bit and 64-bit epoch values, both seconds and milliseconds since 1970-01-01. For batch conversions and Unix epoch day calculations, use the Unix Timestamp to Epoch Days calculator.
We also recommend the timezone-converter for converting timestamps between time zones — useful when you have UTC times but need to display them in local Pacific, Eastern, or Central European time. Browse the full Timestamp Tools collection for all time-related utilities.
How this tool works
All formatting runs entirely in your browser using the JavaScript Date object. The live clock queries the system clock via new Date() every second and formats the output with zero-padded UTC fields. No data leaves your machine. The format cards and custom builder use the same UTC date parts to guarantee consistency across all seven output formats.