RRule Temporal

This library is sponsored by PostalForm 💌 — upload a PDF and we print + mail it via USPS (no printer or stamps needed). The only mailing platform for AI Agents via MCP, and the easiest one for humans!

The first and only fully compliant Recurrence rule (RFC-5545) processing JS/TS library built on the Temporal API, now with support for RFC-7529 (RSCALE / SKIP) for non-Gregorian calendars. The library accepts the familiar RRULE format and returns Temporal.ZonedDateTime instances for easy time‑zone aware scheduling.

See the demo site for an interactive playground.

RRule-temporal was created to advance the JS RRule ecosystem to use Temporal instead of Date, and to properly support cross-timezone and calendar aware recurrence rules, as per the suggestion of rrule.js contributors. jkbrzt/rrule#450 (comment)

Installation

npm install rrule-temporal

Quick start

Parse an ICS snippet and enumerate the occurrences:

import { RRuleTemporal } from "rrule-temporal";

const rule = new RRuleTemporal({
  rruleString: `DTSTART;TZID=UTC:20250101T090000\nRRULE:FREQ=DAILY;COUNT=3`
});

rule.all().forEach(dt => console.log(dt.toString()));
// 2025-01-01T09:00:00[UTC]
// 2025-01-02T09:00:00[UTC]
// 2025-01-03T09:00:00[UTC]

// Only the first 10 events
const firstTen = rule.all((_, i) => i < 10);

Separating DTSTART and RRULE

Per RFC 5545, DTSTART and RRULE are separate properties. You can provide them separately:

import { Temporal } from "@js-temporal/polyfill";

const rule = new RRuleTemporal({
  rruleString: 'FREQ=DAILY;COUNT=5',
  dtstart: Temporal.ZonedDateTime.from('2025-01-01T09:00:00[UTC]')
});

const occurrences = rule.all();

This is useful when:

• Parsing iCalendar files where DTSTART and RRULE are on different lines
• Storing recurrence patterns separately from start dates in databases
• Building rules programmatically from user input

Note on UNTIL (RFC 5545): if DTSTART is a DATE-TIME with a TZID or UTC (Z), UNTIL must be a DATE-TIME in UTC (trailing Z). If DTSTART is VALUE=DATE, UNTIL must be a DATE (no time). Floating DATE-TIME rules (no TZID, no Z) allow a floating UNTIL. In default mode (strict: false), UNTIL=YYYYMMDD with a DATE-TIME DTSTART is accepted for compatibility and treated as inclusive end-of-day in DTSTART's zone (converted to UTC when required). Set strict: true to reject it.

Creating a rule with options

Instead of a full ICS string you can supply the recurrence parameters directly:

import { Temporal } from "@js-temporal/polyfill";

const rule = new RRuleTemporal({
  freq: "DAILY",
  interval: 2,
  count: 3,
  byHour: [9],
  byMinute: [15],
  tzid: "America/Chicago",
  dtstart: Temporal.ZonedDateTime.from({
    year: 2025, month: 4, day: 20,
    hour: 8, minute: 30,
    timeZone: "America/Chicago"
  })
});

rule.all().forEach(dt => console.log(dt.toString()));

Manual options

When creating a rule with individual fields you can specify any of the options below. These correspond to the recurrence rule parts defined in RFC 5545:

Option	Description
freq	Recurrence frequency ("YEARLY", "MONTHLY", "WEEKLY", "DAILY", "HOURLY", "MINUTELY", "SECONDLY").
interval	Interval between each occurrence of freq.
count	Total number of occurrences.
until	Last possible occurrence as Temporal.ZonedDateTime.
byHour	Hours to include (0–23).
byMinute	Minutes to include (0–59).
bySecond	Seconds to include (0–59).
byDay	List of weekday codes, e.g. ["MO", "WE", "FR"].
byMonth	Months of the year (1–12).
byMonthDay	Days of the month (1–31 or negative from end).
byYearDay	Days of the year (1–366 or negative from end).
byWeekNo	ISO week numbers (1–53 or negative from end).
bySetPos	Select n-th occurrence(s) after other filters.
wkst	Weekday on which the week starts ("MO".."SU").
rDate	Additional dates to include.
exDate	Exception dates to exclude.
tzid	Time zone identifier for interpreting dates.
maxIterations	Safety cap when generating occurrences.
includeDtstart	Include DTSTART even if it does not match the pattern.
strict	Enforce RFC 5545 constraints strictly (defaults to false).
dtstart	First occurrence as Temporal.ZonedDateTime.

Querying occurrences

Use the provided methods to enumerate or search for occurrences:

// Get all events within a window
const start = new Date(Date.UTC(2025, 3, 2, 0, 0));
const end = new Date(Date.UTC(2025, 3, 4, 5, 0));
const hits = rule.between(start, end, true);

// Next and previous occurrences
const next = rule.next();
const prev = rule.previous(new Date("2025-05-01T00:00Z"));

Converting to human-readable text

The toText helper converts a rule into a human readable description. UNTIL (and optional DTSTART) dates are locale-aware via toLocaleString.

import { Temporal } from "@js-temporal/polyfill";
import { RRuleTemporal } from "rrule-temporal";
import { toText } from "rrule-temporal/totext";

const rule = new RRuleTemporal({
  rruleString: `DTSTART;TZID=UTC:20250101T090000\nRRULE:FREQ=DAILY;COUNT=3`
});

rule.toString();
// "DTSTART;TZID=UTC:20250101T090000\nRRULE:FREQ=DAILY;COUNT=3"
toText(rule);             // uses the runtime locale, defaults to English
toText(rule, "es");      // Spanish description
toText(rule, "en", { includeDtstart: true }); // include "starting from <DTSTART date>"
toText(rule);
// "every day for 3 times"

const weekly = new RRuleTemporal({
  freq: "WEEKLY",
  byDay: ["SU"],
  byHour: [10],
  dtstart: Temporal.ZonedDateTime.from({
    year: 2025, month: 1, day: 1, hour: 10, timeZone: "UTC"
  })
});

toText(weekly);
// "every week on Sunday at 10 AM UTC"
toText(weekly, "es");
// "cada semana en domingo a las 10 AM UTC"

toText supported languages

toText() currently ships translations for the following languages:

Code	Language
en	English
es	Spanish
hi	Hindi
yue	Cantonese
ar	Arabic
he	Hebrew
zh	Mandarin
de	German
fr	French

NOTE: At build time you can reduce bundle size by defining the TOTEXT_LANGS environment variable (read from process.env), e.g. TOTEXT_LANGS=en,es,ar. When this environment variable is unavailable (such as in browser builds where process is undefined) all languages are included by default.

RFC 7529 (RSCALE / SKIP)

This library implements the iCalendar RSCALE and SKIP extensions described in RFC 7529 for defining recurrence rules in non‑Gregorian calendars and for controlling how invalid dates are handled.

Supported Calendars

Calendar	Description
GREGORIAN	Gregorian calendar (default)
CHINESE	Chinese calendar
HEBREW	Hebrew calendar
INDIAN	Saka/Indian National Calendar

• Spec: RFC 7529 — Non‑Gregorian Recurrence Rules in iCalendar https://www.rfc-editor.org/rfc/rfc7529.html

What RSCALE does:

• Extends RRULE with RSCALE=<calendar> to choose the calendar used for recurrence generation while keeping DTSTART/RECURRENCE‑ID/RDATE/EXDATE in Gregorian.
• Interprets BY* parts (month, day, week, etc.) in the specified calendar when expanding occurrences, then converts the generated dates back to the requested time zone.

What SKIP does:

• Extends RRULE with SKIP=OMIT|BACKWARD|FORWARD (only when RSCALE is present).
• Controls how invalid dates produced by the rule are handled (e.g., Feb 29 in non‑leap years, or months that don’t have the desired day):
  • OMIT (default): drop the invalid occurrence.
  • BACKWARD: move to the previous valid day/month (e.g., Feb 28).
  • FORWARD: move to the next valid day/month (e.g., Mar 1).
• RFC 7529 defines the evaluation order; notably, SKIP may apply after BYMONTH (invalid month) and after BYMONTHDAY (invalid day). If SKIP changes the month and that leads to an invalid day‑of‑month, SKIP is re‑applied for the day step.

Leap months and BYMONTH:

• BYMONTH accepts leap‑month tokens with an L suffix (e.g., 5L) under RSCALE. These are matched against the target calendar’s monthCode (e.g., Chinese M06L, Hebrew M05L).
• Example tokens:
  • Chinese: 5L matches monthCode=M05L (leap 5th) or M06L depending on calendar system; we match by the numeric part + L via monthCode.
  • Hebrew: 5L typically corresponds to Adar I (monthCode=M05L).
  • Numeric months without L (e.g., 5) match the regular month (e.g., monthCode=M05).

Supported RSCALE coverage in this library:

• Frequencies: YEARLY, MONTHLY, WEEKLY with Chinese/Hebrew calendars.
• Constraints: BYMONTH (including leap tokens), BYMONTHDAY, BYDAY (weekday tokens; ordinal support at monthly/yearly levels), BYYEARDAY, BYWEEKNO, BYSETPOS.
• Sub‑daily (DAILY, HOURLY, MINUTELY) behavior:
  • The engine first filters eligible calendar days using BYWEEKNO, BYYEARDAY, BYMONTH, BYMONTHDAY, and simple BYDAY (weekday codes). Then it expands times via BYHOUR/BYMINUTE/BYSECOND.
  • For HOURLY/MINUTELY, INTERVAL alignment is based on elapsed real hours/minutes since DTSTART. Occurrences are kept when the elapsed units are multiples of INTERVAL.
  • Ordinal BYDAY (e.g., 1MO, -1SU) is not interpreted at sub‑daily RSCALE levels; use MONTHLY/YEARLY for these.

Examples

Chinese New Year (1st day of 1st Chinese month), year over year from a Gregorian DTSTART:

DTSTART;VALUE=DATE:20130210
RRULE:RSCALE=CHINESE;FREQ=YEARLY

Hebrew New Year (Tishrei 1) — using BYYEARDAY=1 in Hebrew calendar:

DTSTART;TZID=UTC:20230916T090000
RRULE:RSCALE=HEBREW;FREQ=YEARLY;BYYEARDAY=1;BYHOUR=9

Feb 29 birthday — SKIP strategies:

DTSTART;TZID=UTC:20160229T120000
RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;BYMONTH=2;BYMONTHDAY=29;SKIP=OMIT

DTSTART;TZID=UTC:20160229T120000
RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;BYMONTH=2;BYMONTHDAY=29;SKIP=BACKWARD

DTSTART;TZID=UTC:20160229T120000
RRULE:RSCALE=GREGORIAN;FREQ=YEARLY;BYMONTH=2;BYMONTHDAY=29;SKIP=FORWARD

Notes

• SKIP MUST NOT be present unless RSCALE is present (per RFC 7529).
• Default SKIP is OMIT when RSCALE is present.
• This library surfaces RSCALE/SKIP in toText() at the end of the description: e.g., (RSCALE=HEBREW;SKIP=OMIT).

API

Method	Description
new RRuleTemporal(opts)	Create a rule from an ICS snippet or manual options.
all(iterator?)	Return every occurrence. When the rule has no end the optional iterator is required.
between(after, before, inclusive?)	Occurrences within a time range.
matches(date)	Convenience helper: true if the exact instant is an occurrence (accepts Date or Temporal.ZonedDateTime).
occursOn(date)	Convenience helper: true if any occurrence falls on the given Temporal.PlainDate in the rule's time zone (date-only, ignores time).
next(after?, inclusive?)	Next occurrence after a given date.
previous(before?, inclusive?)	Previous occurrence before a date.
toString()	Convert the rule back into DTSTART and RRULE lines.
toText(rule, locale?, options?)	Human readable description (en, es, hi, yue, ar, he, zh, fr). Options: { includeDtstart?: boolean }.
options()	Return the normalized options object.

Further examples

Enumerating weekdays within a month or rotating through months can be achieved with the more advanced RFC 5545 fields:

// 2nd & 4th Fridays each month at midnight CT, first 6 occurrences
const ruleA = new RRuleTemporal({
  rruleString: `DTSTART;TZID=America/Chicago:20250325T000000\nRRULE:FREQ=MONTHLY;BYDAY=2FR,4FR;BYHOUR=0;BYMINUTE=0;COUNT=6`
});
ruleA.all().forEach(dt => console.log(dt.toString()));

// Rotate yearly through Jan, Jun and Dec at 09:00 UTC
const dtstart = Temporal.ZonedDateTime.from({
  year: 2025, month: 1, day: 10, hour: 9, minute: 0, timeZone: "UTC"
});
const ruleB = new RRuleTemporal({
  freq: "YEARLY",
  interval: 1,
  count: 4,
  byMonth: [1, 6, 12],
  byHour: [9],
  byMinute: [0],
  dtstart
});
ruleB.all().forEach(dt => console.log(dt.toString()));

Working with extra and excluded dates

import { Temporal } from "@js-temporal/polyfill";

const start = Temporal.ZonedDateTime.from({
  year: 2025, month: 1, day: 1, hour: 12, timeZone: "UTC"
});
const ruleC = new RRuleTemporal({
  freq: "WEEKLY",
  count: 5,
  rDate: [start.add({ days: 1 })],           // add one extra day
  exDate: [start.add({ weeks: 2 })],         // skip the third week
  dtstart: start
});

// First five occurrences (with rDate/exDate accounted for)
ruleC.all((_, i) => i < 5).forEach(dt => console.log(dt.toString()));

// Occurrences within a window
const hits = ruleC.between(
  new Date("2025-01-01T00:00Z"),
  new Date("2025-02-01T00:00Z"),
  true
);

Converting between @js-temporal/polyfill and temporal-polyfill

rrule-temporal ships with @js-temporal/polyfill and therefore returns Temporal objects that are from that implementation. If the rest of your codebase (or a third-party package) relies on the lighter temporal-polyfill package or a native Temporal implementation, those objects will not satisfy instanceof checks in your app. This snippet shows how to re-hydrate each recurrence result into the polyfill your project expects.

// rrule-temporal (and its internals) use @js-temporal/polyfill
import { Temporal as RRTTemporal } from "@js-temporal/polyfill";
// your application using temporal-polyfill or native Temporal
import { Temporal as AppTemporal } from "temporal-polyfill";

import { RRuleTemporal } from "rrule-temporal";

/** Weekly rule that fires 4 times starting 5 May 2025, 10 AM America/Chicago. */
const rule = new RRuleTemporal({
  freq: "WEEKLY",
  count: 4,
  dtstart: RRTTemporal.ZonedDateTime.from(
    "2025-05-05T10:00[America/Chicago]"
  ),
});

// Occurrences are ZonedDateTime instances from @js-temporal/polyfill
const rawOccurrences = rule.all();

/** Convert each ZonedDateTime to temporal-polyfill ZonedDateTime. */
const appOccurrences = rawOccurrences.map((zdt) =>
  AppTemporal.ZonedDateTime.from(zdt.toString())
);

// …now `appOccurrences` can be passed anywhere that expects temporal-polyfill in your app

Why .toString()?

Temporal.*.from() accepts ISO 8601 strings (including bracketed time-zone annotations), so calling toString() sidesteps the internal-slot branding that makes polyfill objects incompatible.

Nanosecond precision variant

const appOccurrences = rawOccurrences.map((zdt) =>
  AppTemporal.ZonedDateTime.fromEpochNanoseconds(zdt.epochNanoseconds)
);

Both approaches preserve the original calendar, time-zone and nanosecond accuracy.

Sponsor

If this library saves you time, sponsorship helps keep it maintained.

Primary sponsor: PostalForm