Expand an RRULE or 5-field cron into concrete occurrences with DST handling, exclusions and conflict detection

$0.005 USDC per call · Business, finance and compliance · POST /api/v1/recurrence-expand · Id recurrence-expand

Expands an RFC 5545 RRULE (FREQ DAILY/WEEKLY/MONTHLY/YEARLY, INTERVAL, COUNT, UNTIL, BYDAY with ordinals, BYMONTHDAY, BYMONTH, BYSETPOS, WKST; DTSTART with TZID; EXDATE) or a crontab(5) expression into up to 366 occurrences in a time zone, with the UTC instant of each, DST gap or overlap flags, caller blackout dates, a plain-English reading, and optionally the occurrences where it collides with a second rule. COUNT is applied before EXDATE removal, invalid dates (Feb 30) are skipped, a time in a gap is read with the pre-gap offset and an overlap uses its first occurrence (RFC 5545 3.3.5). Hourly/minutely FREQ, BYHOUR, BYYEARDAY, BYWEEKNO, RDATE, EXRULE, Quartz cron extensions and @macros return `unsupported`. Never reads the clock: the window starts at `from` (or DTSTART).

What you get

Whether a standup, report or billing job fires on the 5th Monday, on a gap day or twice on a fall-back night is decided here instead of guessed.

Call it

Send the JSON body below to https://agents.writerslogic.com/api/v1/recurrence-expand. An unpaid request answers 402 with the price and how to pay; a request that fails with a 5xx status is not charged.

curl -i -X POST https://agents.writerslogic.com/api/v1/recurrence-expand \
  -H 'content-type: application/json' \
  -d '{"kind":"rrule","rule":"DTSTART;TZID=America/New_York:19970902T090000\nRRULE:FREQ=DAILY;COUNT=10","limit":10}'

Input

Field	Type	Required	Description
`kind`	string; one of "rrule", "cron"	yes
`rule`	string; length 0..800	yes	rrule: 'DTSTART;TZID=America/New_York:19970902T090000\nRRULE:FREQ=DAILY;COUNT=10\nEXDATE;TZID=America/New_York:19970903T090000' or just 'FREQ=...' with dtstart. cron: '/15 9-17 * 1-5' (dom and dow both restricted match if either does).
`dtstart`	string; length 0..30	no	Local DTSTART when the rule text has none.
`timeZone`	string; length 0..64	no	IANA zone for local times (required for cron; for rrule unless DTSTART has TZID or Z).
`from`	string; length 0..30	no	Local start of the output window; required for cron, default DTSTART for rrule.
`to`	string; length 0..30	no	Local end of the window, inclusive.
`limit`	integer; 1..366	no	Maximum occurrences returned (default 20).
`exdates`	array<string; length 0..30>; max 200 items	no	Extra excluded local date-times (YYYY-MM-DDTHH:MM[:SS]) or dates (YYYY-MM-DD, excludes that day).
`blackouts`	array<object>; max 50 items	no	Inclusive local date ranges to drop (holidays, freezes).
`durationMinutes`	integer; 0..43200	no	Occurrence length, for conflict overlap.
`other`	object	no	A second rule to compare; conflicts are occurrences whose intervals overlap (equal instants when both durations are 0).

Example request body

{
  "kind": "rrule",
  "rule": "DTSTART;TZID=America/New_York:19970902T090000\nRRULE:FREQ=DAILY;COUNT=10",
  "limit": 10
}

Result

The response is { "data": ..., "_provenance": ... }. data carries these fields; _provenance is a signed W3C Verifiable Credential with a C2PA-style manifest, checked free at POST /api/v1/verify-provenance.

Field	Type	Required	Description
`status`	string; one of "pass", "fail", "unknown", "unsupported"	no	pass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.
`occurrences`	array<object>	no
`count`	integer	no
`description`	string	no
`timeZone`	string	no
`excluded`	array<object>	no
`moreAvailable`	boolean	no
`scanCapped`	boolean	no
`conflicts`	array<object>	no
`comparedThroughUtc`	string	no
`reason`	string	no
`witnesses`	array<object>	no
`versions`	object	no	Every semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
`limits`	array<string>	no
`deterministic`	boolean	no	Always true: pure code, no model.

Pay and connect

Available through: x402 (USDC on Base), MCP. MCP clients reach it through the calendar-deadline-kit package.

Machine-readable

This agent as JSON (schemas, example, OpenAPI operation)
Free signed sample response
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