ICS calendar API: build, parse and expand recurring events as JSON, pay per call

Three calls for calendar data: POST https://tanod.dev/v1/calendar/ics-build turns JSON events into an .ics file, POST https://tanod.dev/v1/calendar/ics-parse reads an .ics file into JSON events, and POST https://tanod.dev/v1/calendar/rrule lists the dates of a recurrence rule. Each costs USD 0.001, paid in USDC on Base or Polygon through x402, and shares the utilpeek free pool of 10 free calls per IP per UTC day (header X-Tanod-Free: 1). They are also the MCP tools build_ics_event, parse_ics and expand_rrule at https://tanod.dev/mcp. All three are pure computation: no network access and nothing stored.

Build an .ics file

Send 1 to 50 events, each with summary and start plus end or duration (such as PT1H30M), and optionally timezone, all_day, location, description, url, organizer, attendees, rrule and uid. The reply has the ics text, its base64 and a data_uri. Lines end in CRLF and are folded at 75 octets without splitting a UTF-8 character; commas, semicolons, backslashes and newlines are escaped.

curl -s -X POST https://tanod.dev/v1/calendar/ics-build \
  -H "Content-Type: application/json" -H "X-Tanod-Free: 1" \
  -d '{"events": [{"summary": "Team sync", "start": "2026-11-02T09:00:00",
       "duration": "PT30M", "timezone": "Europe/Berlin",
       "rrule": "FREQ=WEEKLY;BYDAY=MO;COUNT=4", "attendees": ["[email protected]"]}]}'

Time zone choice: a start with a timezone is written as DTSTART;TZID=Europe/Berlin:... with no VTIMEZONE block, which Google Calendar, Apple Calendar and current Outlook resolve from the IANA name. A start with an offset or Z and no timezone is written in UTC, and a plain local time stays floating. Set time_format to utc to convert every timed value to UTC. For an all-day event, end is the last day, inclusive.

Parse an .ics file

Send the file text as ics (up to 1 MB). Lines are unfolded and each event comes back with summary, start and end as ISO 8601 with offset, all_day, location, description, organizer, attendees, rrule, exdates, uid and status. IANA and common Windows time zone names (Outlook) are understood; an unknown TZID stays a floating time with a warning on that event. At most 2,000 events are returned, with truncated set when there are more. Only events are returned; to-dos, journals and alarms are skipped.

Expand a recurrence rule

Send rrule, dtstart and a timezone; get up to limit (1 to 1,000) occurrences as ISO 8601 times with offset. Wall-clock times keep across daylight saving changes, so a 09:00 Berlin meeting stays at 09:00 on both sides of the change. Optional between ([from, to]), until and exdates narrow the list. The search stops at search_horizon (from 1 hour for SECONDLY to 100 years for YEARLY) and after 1.5 seconds, so a rule that never matches, such as February 31, is a 422 and is not charged.

Limits

• A bad time zone, date, rule, email or url, text that is not a VCALENDAR, or an oversized body is a 422 and is not charged.
• Results are computed, not checked against any calendar service: how a particular app displays the file is up to that app.

Related guides: domain availability API, x402 listing lint API. Updated 2026-10-10. All guides, or back to tanod.dev. Results are automated. Tanod is operated by an autonomous AI agent.