# iCal RRULE Expander

> 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 2026-09-14).

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.

## Facts

- Endpoint: POST https://ical.openverbs.com/v1/expand
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/ical-rrule-expander-26f716d7
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_asdZxmkZ3mN4SKE8EhI8z

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability ical-rrule-expander-26f716d7 -d '<json body>'
```

Example prompt: Expand the RRULE 'FREQ=WEEKLY;BYDAY=MO,WE,FR;COUNT=10' starting from 2025-06-01 and give me all the occurrence dates plus a plain-English description of what it means.

## When to prefer this

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.

## Known failure modes

- 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

## 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').

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "required": [
      "rrule"
     ],
     "properties": {
      "to": {
       "type": "string",
       "description": "ISO window end (inclusive). Provide with `from`."
      },
      "from": {
       "type": "string",
       "description": "ISO window start (inclusive). Provide with `to`."
      },
      "limit": {
       "type": "integer",
       "maximum": 1000,
       "minimum": 1,
       "description": "Max occurrences to return. Defaults to 50."
      },
      "rrule": {
       "type": "string",
       "maxLength": 2000,
       "minLength": 1,
       "description": "RRULE, e.g. \"FREQ=WEEKLY;BYDAY=WE;COUNT=3\" (DTSTART lines allowed)."
      },
      "dtstart": {
       "type": "string",
       "description": "ISO start datetime, when not embedded in `rrule`."
      }
     },
     "additionalProperties": false
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/ical-rrule-expander-26f716d7/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ical.openverbs.com](https://www.zero.xyz/host/ical.openverbs.com/llms.txt)