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RRULE builder

Writing an RRULE by hand means reading RFC 5545 to find out that the last Friday of the month is BYDAY=-1FR. Pick it from a menu instead, and watch the rule and the dates it produces update as you go.

repeats
every N weeks
on these days
ends
your rule
RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR

Every week on Mon, Wed and Fri

Written by serializeRRule(), then read back by describeRRule() — the sentence comes from the rule, not from the form.

the next 6 occurrences, from today
  1. 1Fri, 25 Sept 2026
  2. 2Mon, 28 Sept 2026
  3. 3Wed, 30 Sept 2026
  4. 4Fri, 2 Oct 2026
  5. 5Mon, 5 Oct 2026
  6. 6Wed, 7 Oct 2026
start from a preset
DailyWeekly on ThursdayEvery weekday (Mon–Fri)Monthly on day 24Monthly on the last ThursdayAnnually on 24 September

These are the presets kloq’s own recurrence menu offers, from presetsFor(). Already have a rule? Explain it instead.

—where this comes from

It is one function out of a calendar.

This page runs serializeRRule(), describeRRule() and presetsFor() from kloq — the same code that ships in kloq, not a re-implementation. Every interaction in the calendar is built to this standard, which is the whole pitch.

Read the docsTry the calendarnpm install kloq

—also free

The other four.

Spring to CSS linear() converter

stiffness · damping · samples → one CSS value

RRULE explainer

RFC 5545 in, plain English and real dates out

Natural-language date parser

a sentence in, an event and its source offsets out

Time zone overlap map

day, night, and the hours everyone is awake