ISO 8601 / RFC 3339 Formatter

Paste any date or epoch and read it in every standard form at once — offset decoded, standards checked, entirely on this device.

0 bytes uploaded

Input — paste a date, timestamp or epoch value

awaiting inputEpoch unitOffset zone

The local-offset row renders in this zone, and a date with no offset of its own is read in it — flagged inline when that happens.

Every standard form of your date appears here as you type — press Now for the current instant.

Offset, decoded

Which standards does this text satisfy?

ISO 8601
RFC 3339
RFC 2822

0 B · awaiting input

Press ? for shortcuts

Do it offline:$ date -u -Iseconds -d @1784937600

How to use it

Paste a date, timestamp or epoch value — or press Now for the current instant.
Read the same instant in all eleven rows, each with its own copy control.
Read the offset panel: the designator's token, sign and distance from UTC, decoded.
Check the standards strip — pass or fail per standard, every verdict chip-explained.

One paste, every standard form at once: ISO 8601 extended, basic, ordinal and week dates, RFC 3339, RFC 2822, HTTP-date, SQL and epoch rows for one instant. An offset panel decodes the designator, and three verdict chips answer the real question — which standard does this exact text satisfy? Nothing leaves this device.

Examples

2026-07-25T09:00:00+05:30

2026-07-25T03:30:00Z

The +05:30 designator sits 330 minutes east, so the panel reads 5 h 30 min ahead of UTC and the UTC row lands at 03:30 — the one shape ISO 8601 and RFC 3339 agree on completely.

1784937600

2026-07-25T00:00:00Z

An epoch value is a count, not a notation: all three verdict chips honestly fail — no syntax to judge — while the table still renders every form; the badge names the unit.

Sat, 25 Jul 2026 09:00:00 GMT

2026-07-25T09:00:00Z

The e-mail and HTTP header shape: RFC 2822 passes, both ISO verdicts fail, and the named zone GMT draws an obsolete-form chip — new output takes numeric offsets like +0000 instead.

2026-W30-6

2026-07-25T00:00:00Z

A week date — Saturday of week 30, day 206 in the ordinal row — landing on the instant example 2 named. ISO 8601 passes; RFC 3339 fails, its chip naming the extended-calendar-only rule.

Every example on this page is executed against the same engine that powers the tool, on every build.

Gotchas worth knowing

T versus space, and lowercase t and z

A space where the T belongs fails both verdicts, chip attached, though the value still converts via a lenient rung. Lowercase t or z cuts the other way: RFC 3339 §5.6 permits it, so the verdicts hold under a nuance chip.

Comma or dot before the fraction

A decimal comma is legal ISO 8601 — 09:00:00,5 names half a second past nine — while RFC 3339 admits only the dot, splitting the verdicts. Either spelling carries its half second into the UTC row as .500.

Week, ordinal and basic forms are ISO-only

2026-W30-6, 2026-206 and 20260725T093000Z are all valid ISO 8601 and all fail RFC 3339. One deliberate divergence: a bare 20260725 reads here as a basic calendar date, while the Unix Timestamp Converter reads the same eight digits as epoch seconds.

The offset is optional in ISO 8601, mandatory in RFC 3339

2026-07-25T09:00:00 with nothing after it is legal ISO 8601 local time; RFC 3339 refuses any timestamp that cannot state its distance from UTC. This page reads the zone-less form in your selected zone — with a warning saying so.

Z, +00:00 and -00:00 are three different statements

All three pin one instant — identical rows here. Z and +00:00 assert UTC and pass both standards; -00:00 means the local offset is unknown (RFC 3339 §4.3), and ISO 8601 outlaws it — zero takes the plus sign there.

Common errors

Not a timestamp or a recognizable date — try 1784937600 or 2026-07-25T00:00:00Z: Nothing on the parse ladder matched — not the ISO grammars, not RFC 2822, not an epoch count. Reduced precision such as 2026-07, durations like PT1H30M and intervals land here on purpose, never guessed at.
Outside the representable range — ECMAScript dates cover ±8,640,000,000,000,000 ms around 1970-01-01T00:00:00Z (about 271821 BCE to 275760 CE): ECMA-262 caps date arithmetic at ±100,000,000 days from the epoch. The boundary instant +275760-09-13T00:00:00Z still converts; one millisecond past it is refused. Expanded six-digit years are the usual trigger here.
Unknown time zone "Asia/Kolkatta" — use an IANA name like "Europe/London": The offset zone must be a name your browser's zone database knows; one wrong letter — Kolkatta for Kolkata — fails the lookup before parsing begins. In practice it arrives via a hand-edited share link.
Input is larger than the 4 KB limit for this tool. Paste a single date or timestamp — for files use the CLI: date -u -Iseconds -d @1784937600: This page converts exactly one value, so text past 4 KB cannot be a date and is declined whole, your paste kept. Multi-line timestamp lists — and unit education — belong to the Unix Timestamp Converter, built for batches.

FAQ

ISO 8601 vs RFC 3339 — what is the difference?

RFC 3339 is a small internet profile of ISO 8601: one shape — extended calendar date, T, full time, mandatory numeric offset, dot fractions — where the parent standard also grants week and ordinal dates, basic forms, comma fractions and local times. Nearly everything the RFC accepts is ISO 8601 too; -00:00 is the exception it defines and ISO forbids. When both rows coincide, a profile-equality chip says so.

Do Z, +00:00 and -00:00 mean the same thing?

The same instant, not the same knowledge. Emit Z or +00:00 when a system truly runs in UTC; reserve -00:00 for RFC 3339's narrow case of a timestamp whose local offset nobody recorded — strict ISO 8601 consumers may reject that spelling.

Is a date-time without an offset valid?

As ISO 8601 local time, yes — but it names a wall-clock reading, not an instant: 09:00 happens at a different moment in every zone, which is why RFC 3339 and RFC 2822 refuse the form. Exchange timestamps with the offset attached.

How do I print an ISO 8601 timestamp from the command line?

GNU date has a flag for it: date -u -Iseconds prints the current UTC instant with a numeric +00:00 offset, and -d @1784937600 formats that epoch instead of now. BSD and macOS date accept -Iseconds but spell the epoch flag -r. In code, JavaScript's toISOString() and Python's datetime.isoformat() emit it directly.

Keyboard shortcuts

⌘/Ctrl + Enter: Re-run the conversion.
⌘/Ctrl + S: Download the table as .txt.
⌘/Ctrl + C: Copy the ISO 8601 UTC row while nothing is selected.
⌘/Ctrl + Shift + C: Copy that row even over a selection.
t: Cycle the theme (inactive while typing).
? or ⌘/Ctrl + /: Show the keyboard help overlay.
Esc: Dismiss the topmost dialog; input stays put.

Nothing you paste here leaves this tab. State only ever travels in links you explicitly create.

RFC 3339 — Date and Time on the Internet: Timestamps · ISO 8601 — Date and time format (iso.org) · RFC 9110 §5.6.7 — HTTP Date/Time Formats (IMF-fixdate) · RFC 2822 §3.3 — Date and Time Specification

Last reviewed: 2026-08-07