DateTime Tools for Developers
8 free DateTime tools — Unix timestamp converter, ISO 8601 validator, time zone converter, format converter, epoch precision, duration formatter, and more. All run entirely in your browser.
Unix Timestamp Converter
Convert Unix timestamps to human-readable dates and back — both seconds and milliseconds precision.
ISO 8601 Date Validator
Validate and format ISO 8601 / RFC 3339 dates — the standard format for APIs, databases, and JSON.
Date Format Converter
Convert dates between MM/DD/YYYY, DD/MM/YYYY, YYYY-MM-DD, RFC 2822 and 20+ other formats.
Time Zone Converter
Convert any datetime between IANA time zones — UTC, EST, IST, GMT, JST, and 400+ more.
Epoch Time Converter
Convert epoch time across precision levels — seconds, milliseconds, microseconds, nanoseconds.
Duration Formatter
Convert milliseconds to human-readable durations — "3h 15m 22s", "2 days 4 hours", or ISO 8601 duration.
Date Difference Calculator
Calculate time between two dates — years, months, weeks, days, hours, minutes, business days.
Strftime Format Builder
Visual builder for strftime / Moment.js / date-fns format strings with live preview.
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Why use OpenFormatter for DateTime?
400+ IANA time zones
Browser-native Intl.DateTimeFormat gives correct DST handling for every IANA time zone — no time-zone database to maintain.
RFC 3339 + ISO 8601
Validators and converters target the exact spec used by JSON APIs, OpenAPI, and SQL TIMESTAMP — including edge cases like fractional seconds and offsets.
Auto-detect precision
Epoch and timestamp tools auto-detect seconds vs milliseconds vs nanoseconds based on digit count — no manual mode switch.
No tracking
No analytics on dates you paste. All conversions happen in your browser using the standard Web Date and Intl APIs.
Frequently Asked Questions
What is a Unix timestamp?
A Unix timestamp is the number of seconds (or milliseconds) elapsed since January 1, 1970 UTC, called the "epoch". Most operating systems, databases, and APIs use this format because it is timezone-agnostic, sortable, and storage-efficient. JavaScript uses millisecond precision (Date.now()), Unix shells use seconds, Go time.UnixNano uses nanoseconds.
What is the difference between ISO 8601 and RFC 3339?
RFC 3339 is a strict subset of ISO 8601 designed for internet protocols. The main differences: RFC 3339 requires a separator (T or space) between date and time, requires a timezone designator, and forbids some ISO 8601 forms like "20230115" (no separators). Most APIs that say "ISO 8601" actually expect RFC 3339. Examples: 2026-05-01T12:34:56Z (RFC 3339), 2026-W18-5 (ISO 8601 only).
Why does my JavaScript Date.parse() return wrong dates?
JavaScript Date.parse() is notoriously inconsistent across browsers for non-ISO formats. The only format guaranteed to work cross-browser is ISO 8601 / RFC 3339. For other formats, use a library like date-fns or Day.js, or convert the input to ISO 8601 first using our Date Format Converter.
How do I handle time zones correctly?
Always store dates in UTC and convert to the user's local time zone for display. Use IANA time zone identifiers like "America/New_York" or "Asia/Kolkata" — never offsets like "EST" or "GMT+5:30" because they don't handle DST. Modern browsers support Intl.DateTimeFormat with timeZone option for accurate conversion.
Why is my epoch timestamp 13 digits not 10?
Unix timestamps are traditionally 10 digits (seconds since epoch), but JavaScript and many modern APIs use 13 digits (milliseconds since epoch). PostgreSQL's extract(epoch from ...) returns seconds with microsecond precision (16 digits). Go's time.UnixNano returns nanoseconds (19 digits). Our Epoch Time Converter auto-detects the precision based on digit count.
What is the Y2038 problem?
On January 19, 2038 at 03:14:07 UTC, 32-bit signed Unix timestamps will overflow. Systems using 32-bit time_t will wrap to December 1901. This affects legacy embedded systems, old C code, and some database fields. Modern 64-bit systems are unaffected. If you store epoch timestamps as INT4 in PostgreSQL or use 32-bit time in C, plan a migration.
How do I format a duration like "3h 15m"?
JavaScript has no built-in duration formatter. Use Math.floor() to extract hours, minutes, and seconds from a millisecond value: const h = Math.floor(ms / 3600000); const m = Math.floor((ms % 3600000) / 60000); const s = Math.floor((ms % 60000) / 1000). Or use our Duration Formatter for a clean output. ISO 8601 has its own duration format like "PT3H15M22S".
Are these tools accurate for historical dates?
Yes for dates from 1970 onward (Unix epoch start). For pre-1970 dates, use ISO 8601 strings — Unix timestamps can be negative but support is inconsistent across languages. For dates before 1582 (Gregorian calendar adoption), historical accuracy depends on the proleptic Gregorian assumption used by most languages — be aware that historians may use Julian dates for events before 1582.
Need other developer tools?
Pair the DateTime tools with the rest of OpenFormatter — 200+ tools, all browser-side.