What is ICS?

ICS (.ics) files contain calendar and scheduling information in the iCalendar format. They store events with details like start/end times, locations, attendees, reminders, and recurrence rules. ICS is a plain text format that works across all major calendar applications, making it the universal standard for sharing calendar data.

You can email ICS files as meeting invitations, subscribe to ICS URLs for dynamic calendars (sports schedules, holidays), or export/import events between calendar apps. The format supports single events or entire calendars with multiple events. Most email clients automatically recognize ICS attachments and offer to add events to your calendar.

Did you know? You can subscribe to ICS URLs in calendar apps for automatic updates - perfect for sports schedules!

History

iCalendar was developed by the IETF Calendaring and Scheduling Working Group to create a standard for calendar data exchange across different platforms.

Key Milestones

  • 1998: RFC 2445 iCalendar standard
  • 2000s: Adoption by major calendar apps
  • 2009: RFC 5545 updated standard
  • 2010s: Cloud calendar services use ICS
  • Present: Universal calendar interchange format

Key Features

Core Capabilities

  • Events: Meetings, appointments, reminders
  • Recurrence: Daily, weekly, monthly patterns
  • Time Zones: Proper timezone handling
  • Attendees: Participant lists with RSVP
  • Alarms: Reminders before events
  • Attachments: Links and documents

Common Use Cases

Meeting Invites

Email calendar invitations

Calendar Sync

Share calendars between apps

Event Schedules

Sports, concerts, holidays

Data Export

Backup calendar data

Advantages

  • Universal calendar standard
  • Cross-platform compatibility
  • Human-readable text format
  • Supports complex recurrence
  • Automatic email integration
  • Dynamic calendar subscriptions

Disadvantages

  • Complex format specification
  • Inconsistent app implementations
  • Timezone handling issues
  • Large files for many events
  • No built-in encryption

Technical Information

Format Specifications

Specification Details
File Extension .ics, .ifb, .ical
MIME Type text/calendar
Format Type Calendar data
Encoding UTF-8
Standard RFC 5545
Structure VCALENDAR components

Common Tools

  • Apps: Google Calendar, Outlook, Apple Calendar
  • Editors: Text editors, calendar apps
  • Libraries: ical.js, iCalendar.js