Skills
skills/johnlarkin1/claude-code-extensions/ics-generator

ics-generator

SKILL.md

ICS Calendar File Generator

Generate valid .ics (iCalendar RFC 5545) files from natural language event descriptions. Files open directly in Apple Calendar.

Quick Start

Minimal valid single-event file:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250115T140000
DTEND;TZID=America/New_York:20250115T150000
SUMMARY:Team Meeting
UID:550e8400-e29b-41d4-a716-446655440000@claude.ai
DTSTAMP:20250115T120000Z
END:VEVENT
END:VCALENDAR

Workflow

  1. Parse the user's natural language description for: title, date/time, duration, location, recurrence, attendees, reminders
  2. Resolve date references like "next Tuesday", "this Friday at 3pm" relative to the current date
  3. Default timezone to America/New_York unless the user specifies otherwise
  4. Generate a UUID v4 for the UID field: <uuid4>@claude.ai
  5. Set DTSTAMP to the current UTC timestamp
  6. Build VEVENT block(s) with all applicable properties
  7. Add VALARM for reminders (default: 15 minutes before if not specified)
  8. Add RRULE for recurring events
  9. Wrap in VCALENDAR with standard headers
  10. Write the .ics file to the current working directory and open it with open <filename>.ics

Defaults

  • Timezone: America/New_York (Eastern) — do NOT ask the user for timezone unless the event is clearly in another zone
  • Auto-open: Always run open <filename>.ics after writing the file
  • Save location: Current working directory
  • Duration: 1 hour if not specified
  • Reminder: 15 minutes before if not specified
  • Filename: kebab-case from the event summary, e.g., team-meeting.ics

VCALENDAR Wrapper

Every .ics file starts and ends with:

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
<VTIMEZONE blocks>
<VEVENT blocks>
END:VCALENDAR

Date/Time Formats

Timed events (with timezone)

DTSTART;TZID=America/New_York:20250115T140000
DTEND;TZID=America/New_York:20250115T150000

All-day events (DATE only, no time component)

DTSTART;VALUE=DATE:20250115
DTEND;VALUE=DATE:20250116

Note: DTEND for all-day events is exclusive — a single all-day event on Jan 15 uses DTEND of Jan 16.

UTC times

DTSTART:20250115T190000Z

Event Properties

Required

Property Description Example
DTSTART Start date/time DTSTART;TZID=America/New_York:20250115T140000
DTEND or DURATION End time or duration DTEND;TZID=America/New_York:20250115T150000 or DURATION:PT1H
SUMMARY Event title SUMMARY:Team Standup
UID Unique identifier UID:550e8400-e29b-41d4-a716-446655440000@claude.ai
DTSTAMP Creation timestamp (UTC) DTSTAMP:20250115T120000Z

Optional

Property Description Example
DESCRIPTION Event details/notes DESCRIPTION:Discuss Q1 roadmap
LOCATION Event location LOCATION:Conference Room A
URL Related link URL:https://meet.google.com/abc-defg-hij
ORGANIZER Event organizer ORGANIZER;CN=John:mailto:john@example.com
ATTENDEE Invited person ATTENDEE;ROLE=REQ-PARTICIPANT;RSVP=TRUE;CN=Jane:mailto:jane@example.com
STATUS Event status STATUS:CONFIRMED (or TENTATIVE, CANCELLED)
TRANSP Time transparency TRANSP:OPAQUE (busy) or TRANSP:TRANSPARENT (free)
CATEGORIES Event categories CATEGORIES:MEETING,WORK
PRIORITY Priority (0-9) PRIORITY:1 (1=highest, 9=lowest, 0=undefined)

DURATION format

DURATION:PT1H          → 1 hour
DURATION:PT30M         → 30 minutes
DURATION:PT1H30M       → 1 hour 30 minutes
DURATION:P1D           → 1 day
DURATION:P1W           → 1 week

Text Escaping

Escape these characters in text property values:

  • Backslash: \\
  • Semicolon: \;
  • Comma: \,
  • Newline: \n

Example:

DESCRIPTION:Agenda:\n1. Review\n2. Planning\nLocation: Room 4\, Building A

Reminders (VALARM)

Add inside a VEVENT block:

BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM

Common trigger durations

Natural language TRIGGER value
At time of event TRIGGER:PT0S
5 minutes before TRIGGER:-PT5M
10 minutes before TRIGGER:-PT10M
15 minutes before TRIGGER:-PT15M
30 minutes before TRIGGER:-PT30M
1 hour before TRIGGER:-PT1H
2 hours before TRIGGER:-PT2H
1 day before TRIGGER:-P1D
1 week before TRIGGER:-P1W

Recurring Events (RRULE)

Add an RRULE property to the VEVENT:

RRULE:FREQ=WEEKLY;BYDAY=TU,TH;COUNT=10

Common patterns

Pattern RRULE
Every day RRULE:FREQ=DAILY
Every weekday RRULE:FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR
Every week RRULE:FREQ=WEEKLY
Every 2 weeks RRULE:FREQ=WEEKLY;INTERVAL=2
Every month (same date) RRULE:FREQ=MONTHLY
Every month (e.g., 2nd Tuesday) RRULE:FREQ=MONTHLY;BYDAY=2TU
Every year RRULE:FREQ=YEARLY
Weekly until a date RRULE:FREQ=WEEKLY;UNTIL=20250630T235959Z
Weekly for 10 occurrences RRULE:FREQ=WEEKLY;COUNT=10

Excluding dates (EXDATE)

EXDATE;TZID=America/New_York:20250219T140000
EXDATE;TZID=America/New_York:20250226T140000

Timezone Handling

Default: America/New_York

Always include this VTIMEZONE block when using Eastern time:

BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=11
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYDAY=2SU;BYMONTH=3
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE

Common timezone name mapping

User says TZID
Eastern, ET, EST, EDT America/New_York
Central, CT, CST, CDT America/Chicago
Mountain, MT, MST, MDT America/Denver
Pacific, PT, PST, PDT America/Los_Angeles
Arizona America/Phoenix
Hawaii, HST Pacific/Honolulu
London, GMT, BST Europe/London
Paris, CET, CEST Europe/Paris
Tokyo, JST Asia/Tokyo

See references/ics-format.md for full VTIMEZONE definitions for all common timezones.

Line Folding

Lines longer than 75 octets MUST be folded by inserting a CRLF followed by a single whitespace character (space or tab). In practice, keep property lines under 75 characters when possible.

DESCRIPTION:This is a very long description that would exceed the seventy-f
 ive octet limit so it is folded onto the next line with a leading space.

Key Gotchas

  1. Line endings: Use CRLF (\r\n) line endings throughout the file
  2. DTEND is exclusive: An all-day event on Jan 15 needs DTEND;VALUE=DATE:20250116
  3. UID must be globally unique: Always generate a fresh UUID v4 for each event
  4. DTSTAMP is required: Always set to current UTC time
  5. VTIMEZONE must precede VEVENT: Place timezone definitions before events in the file
  6. No trailing whitespace: Lines must not end with spaces or tabs
  7. Property names are case-insensitive but conventionally UPPERCASE
  8. Empty lines: No blank lines allowed between properties within a component
  9. UNTIL in RRULE must be UTC: UNTIL=20250630T235959Z (with Z suffix)
  10. Multi-value properties: Use comma separation: EXDATE;TZID=America/New_York:20250219T140000,20250226T140000

Complete Examples

Simple meeting

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=11
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYDAY=2SU;BYMONTH=3
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250115T140000
DTEND;TZID=America/New_York:20250115T150000
SUMMARY:Team Standup
DESCRIPTION:Weekly sync to review progress and blockers
LOCATION:Conference Room B
UID:a1b2c3d4-e5f6-7890-abcd-ef1234567890@claude.ai
DTSTAMP:20250115T120000Z
STATUS:CONFIRMED
TRANSP:OPAQUE
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

All-day event

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250220
DTEND;VALUE=DATE:20250221
SUMMARY:Company Holiday
UID:b2c3d4e5-f6a7-8901-bcde-f12345678901@claude.ai
DTSTAMP:20250115T120000Z
TRANSP:TRANSPARENT
END:VEVENT
END:VCALENDAR

Multi-day event

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250310
DTEND;VALUE=DATE:20250313
SUMMARY:Team Offsite
DESCRIPTION:Annual team offsite in Austin
LOCATION:Austin\, TX
UID:c3d4e5f6-a7b8-9012-cdef-123456789012@claude.ai
DTSTAMP:20250115T120000Z
END:VEVENT
END:VCALENDAR

Recurring weekly meeting with exceptions

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=11
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYDAY=2SU;BYMONTH=3
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250107T100000
DTEND;TZID=America/New_York:20250107T103000
SUMMARY:1:1 with Manager
RRULE:FREQ=WEEKLY;BYDAY=TU;UNTIL=20250701T035959Z
EXDATE;TZID=America/New_York:20250218T100000
EXDATE;TZID=America/New_York:20250527T100000
UID:d4e5f6a7-b8c9-0123-defa-234567890123@claude.ai
DTSTAMP:20250115T120000Z
STATUS:CONFIRMED
BEGIN:VALARM
TRIGGER:-PT10M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

Multiple events in one file

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Claude//ICS Generator//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:America/New_York
BEGIN:STANDARD
DTSTART:19701101T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=11
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19700308T020000
RRULE:FREQ=YEARLY;BYDAY=2SU;BYMONTH=3
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250120T090000
DTEND;TZID=America/New_York:20250120T091500
SUMMARY:Morning Standup
UID:e5f6a7b8-c9d0-1234-efab-345678901234@claude.ai
DTSTAMP:20250115T120000Z
BEGIN:VALARM
TRIGGER:-PT5M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250120T140000
DTEND;TZID=America/New_York:20250120T150000
SUMMARY:Design Review
LOCATION:Zoom
UID:f6a7b8c9-d0e1-2345-fabc-456789012345@claude.ai
DTSTAMP:20250115T120000Z
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

Reference

See references/ics-format.md for complete property tables, full RRULE syntax, all timezone definitions, and the validation checklist.

Weekly Installs
3
Repository
johnlarkin1/cla…tensions
GitHub Stars
17
First Seen
Feb 27, 2026
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