rrule-ts

RFC 5545 RRULE parser, validator, stringifier, and expander. Temporal-native, zero runtime dependencies.

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Why another RRULE library?

Existing libraries like rrule and rrule-temporal share a common limitation: they rely on Date, moment.js, or custom date math, which means daylight-saving-time transitions, leap seconds, and non-Gregorian calendars require workarounds. rrule-ts is built from scratch on the TC39 Temporal proposal, the modern, correct datetime API now shipping in Node.js 26 and modern browsers.

Key differentiators vs the alternatives:

	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 (planned)	No	No
Strict RFC 5545 validation	Yes	Partial	Partial
Subpath tree-shaking	Yes	No	No

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Packages

Package	Description
rrule-ts	Core: parse, validate, stringify, expand, iterate, RRuleSet

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Philosophy

• Zero runtime dependencies. The library reads globalThis.Temporal when available (Node >= 26, modern browsers) and falls back to any Temporal implementation injected via setTemporal(). No polyfill is bundled, keeping library size near zero.
• Strict by default. Parse returns a typed Result, never throws on user input. Validation reports all errors with stable rule IDs, not just the first.
• Tree-shakeable subpaths. Human-readable text rendering and locale packs live in separate subpaths (rrule-ts/text, rrule-ts/locales/en) so bundles only pay for what they import.
• Differential conformance. A conformance test harness comparing this library against a reference Python dateutil.rrule implementation is planned for the expansion phase.

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Installation

npm install rrule-ts

On Node.js < 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, globalThis.Temporal is used automatically.

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Quick start

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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Contributing

See CONTRIBUTING.md.

Security

See SECURITY.md.

Sponsors

Development is supported through GitHub Sponsors.

License

MIT. See LICENSE.