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DATE, TIME & TIMEZONE · LOCAL WORKBENCH

Date Format Tester

Render Unicode or strftime date patterns against a chosen UTC date and time; inspect ISO week-year, ordinal day, token references, common formats and New Year mistakes.

DATE, TIME & TIMEZONE · LOCAL WORKBENCH · BROWSER WORKSPACE

Test your date pattern. Catch the New Year bug before it ships.

01 · TEST THE PATTERNUTC · EXPLICIT INPUT
TRY A KNOWN FORMATLOAD PATTERN
Pattern tokens are not interchangeable.Unicode: MM means month, mm means minutes; yyyy is calendar year and YYYY is ISO week-year. strftime: %m is month and %M is minutes.
02 · RENDERED RESULTUNICODE TOKENS
RENDERS AS · UTC2020-12-365 14:05:09
Pattern reviewYour pattern uses Y, the ISO week-numbering year. For this date the calendar year is 2019, while the week year is 2020; the rendered value is 2020-12-365 14:05:09. Use lowercase yyyy unless you deliberately need a week-year.
CALENDAR YEAR2019
ISO WEEK-YEAR2020week W01
DAY OF YEAR365of 365
03 · COMMON FORMATS, SAME MOMENT9 EXAMPLES
ISO dateyyyy-MM-dd2019-12-31
ISO 8601 in UTCyyyy-MM-dd'T'HH:mm:ss'Z'2019-12-31T14:05:09Z
day first — most of the worlddd/MM/yyyy31/12/2019
month first — ambiguous with the line aboveMM/dd/yyyy12/31/2019
long formEEEE d MMMM yyyyTuesday 31 December 2019
ordinal dateyyyy-DDD2019-365
ISO week dateyyyy-'W'ww-e2019-W01-e
24-hour timeHH:mm14:05
12-hour timehh:mm a02:05 PM
04 · TOKEN REFERENCE17 TOKENS
yyyy2019calendar year · usually preferred
yy19two-digit calendar year
YYYY2020ISO week-numbering year — not the calendar year
MM12month, two digits · usually preferred
MMMDecmonth, short name
MMMMDecembermonth, full name
dd31day of the month · usually preferred
DDD365day of the year
EEETueweekday, short
EEEETuesdayweekday, full
HH14hour, 24-clock · usually preferred
hh02hour, 12-clock
mm05minutes · usually preferred
ss09seconds · usually preferred
aPMAM or PM
ww01ISO week number
'T'Ta literal T — quotes make it literal
Timezone and runtime limits

All values are interpreted as UTC so the sample is repeatable. This is a focused token tester, not a full implementation of every ICU, Java, .NET, Moment or platform-specific date token. Unknown tokens stay literal. Use the target library to confirm compatibility before shipping.

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Runs in this browser. Results are estimates or editing cues. Review the assumptions and source-specific limits before using them in a consequential decision.

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How this app works

Render Unicode or strftime date patterns against a chosen UTC date and time; inspect ISO week-year, ordinal day, token references, common formats and New Year mistakes. Results update as you adjust inputs and stay in this browser.