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iCal RRULE Expander
x402
iCal RRULE Expander is a paid API for AI agents from ical.openverbs.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-28).
Expands an RFC 5545 RRULE recurrence rule string into a list of concrete occurrence datetimes, with an optional human-readable description of the recurrence pattern.
Price / call$0.002
Success—
StatusUnknown
How this service works
Expand an RRULE recurrence rule into its occurrence datetimes, with a human-readable description.
Output
Returns a list of ISO 8601 datetime strings representing each computed occurrence of the recurrence rule within the requested constraints, along with a human-readable English description of the recurrence pattern (e.g. 'Every Monday and Wednesday for 3 weeks').
Example use cases
Preview recurring meeting schedule
“I have a recurring standup with this rule: FREQ=WEEKLY;BYDAY=TU,TH;UNTIL=20251231T000000Z, starting June 2 2025 — can you expand it so I can see all the actual meeting dates before I send the invite?”
Find occurrences within a date window
“Given the RRULE FREQ=MONTHLY;BYDAY=1MO starting 2025-01-01, list every occurrence that falls between July 1 2025 and December 31 2025.”
Sanity-check a complex RRULE
“Can you expand FREQ=DAILY;INTERVAL=2;COUNT=7 from start date 2025-06-10 and tell me in plain English what the pattern is — I want to make sure I wrote the rule correctly?”
Technical details
Endpoint
POSThttps://ical.openverbs.com/v1/expand?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need to materialize concrete datetime instances from an RFC 5545 RRULE string — for example to display a schedule, validate a rule, check for conflicts, or feed occurrences into a downstream calendar or notification system. Prefer it over manual parsing when you also want a human-readable description of the pattern. It complements the sibling .ics builder and parser endpoints on the same platform.
Side effects
- Invalid or malformed RRULE string returns a 400 error
- Missing required `rrule` field returns a validation error
- Providing a window (`from`/`to`) without a DTSTART may yield unexpected results if no DTSTART is embedded in the rule
- Requesting more than 1000 occurrences via `limit` is rejected
- An open-ended RRULE with no COUNT, UNTIL, or window bounds may return the default 50 occurrences
- Malformed ISO datetime strings for `dtstart`, `from`, or `to` return a 400 error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| to | string | ISO window end (inclusive). Provide with `from`. |
| from | string | ISO window start (inclusive). Provide with `to`. |
| limit | integer | Max occurrences to return. Defaults to 50. |
| rrule | string | RRULE, e.g. "FREQ=WEEKLY;BYDAY=WE;COUNT=3" (DTSTART lines allowed). |
| dtstart | string | ISO start datetime, when not embedded in `rrule`. |
Tags
x402
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