RFC 5545 recurrence rules. Correct by construction.

Why rrule-ts?

Temporal-native

Built on the TC39 Temporal proposal. Uses globalThis.Temporal on Node 26+ and modern browsers. Falls back to any Temporal polyfill via setTemporal(). No date math hacks.

Zero runtime dependencies

The library has no bundled dependencies. Temporal is accessed via globalThis.Temporal or an injected polyfill. Your bundle only pays for what you import.

TypeScript-first

Every function has precise return types. parse() returns Result<RRuleOptions, string>. validate() returns Result<RRuleOptions, ValidationError[]>. No silent failures.

Differential conformance suite

Every expansion result is compared against python-dateutil 2.9.0 as the ground-truth oracle, and rrule.js as a known-divergence reference. Behavior is provably correct, not just tested in isolation.

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How it compares

	rrule-ts	rrule	rrule-temporal
Temporal-native	Yes	No	Partial
Zero runtime dependencies	Yes	No	No
TypeScript-first	Yes	Types via @types	Yes
Differential conformance suite	Yes	No	No
Strict RFC 5545 validation	Yes	Partial	Partial
Subpath tree-shaking	Yes	No	No

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Install

npm install rrule-ts

On Node.js versions below 26, inject a Temporal polyfill before using date-expansion features:

import { setTemporal } from 'rrule-ts'
import { Temporal } from 'temporal-polyfill'

setTemporal(Temporal)

On Node.js 26 and above, globalThis.Temporal is used automatically.

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Quick example

import { parse, validate, stringify } from 'rrule-ts'

const result = parse('RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR;COUNT=10')
if (!result.ok) {
  console.error(result.error)
  process.exit(1)
}

const validation = validate(result.value)
if (!validation.ok) {
  for (const e of validation.error) {
    console.error(`${e.ruleId}: ${e.message}`)
  }
  process.exit(1)
}

console.log(stringify(validation.value))
// RRULE:FREQ=WEEKLY;COUNT=10;BYDAY=MO,WE,FR

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Get started

Introduction

Understand the design, install the library, and set up the Temporal polyfill. Read the introduction

Quickstart

Go from a RRULE string to validated, expanded occurrences in minutes. Read the quickstart

Conformance

See how every expansion result is verified against python-dateutil and rrule.js. View the conformance suite

GitHub

Source code, issues, and the differential conformance corpus. View on GitHub