ICalendar

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File Format
Name ICalendar
Ontology
Extension(s) .ics, .ical, .ifb, .icalendar
MIME Type(s) text/calendar

iCalendar, or ICS, is a standardized format for storing and transmitting calendar data, including scheduled events and "to-do" lists. People often associate it with Apple's iCal program (now just "Calendar"), but it is a standardized format with an official RFC document (RFC 5545) and the format is supported by many calendar programs including Google Calendar and Mozilla Lightning (plugin for Thunderbird). Microsoft Outlook does the typical Microsoft thing of supporting something vaguely resembling the standard but full of quirky incompatibilities.

Subscribable calendars can be created by creating and updating a file in this format that is accessible on the Internet via a URL (where the URL stays the same even as the file is modified to reflect updates to the calendar events). Various calendar software (such as the calendar app on iOS or Android devices) will let you subscribe to a calendar URL and will automatically fetch updates so that whenever you view the calendar in your app it will be up-to-date. Read-only access to subscribed calendars can be done with the HTTP protocol, but the CalDAV protocol (based on WebDAV and defined by RFC 4791) permits both reading and writing for full calendar syncing across multiple users (requiring both a client and a server that supports this protocol, and whatever permissions are needed to have access to the particular calendar involved).

Individual event listings can also be provided in iCalendar form to be downloaded, attached to e-mail, and so on. This is often done in websites devoted to particular events, conventions, meetings, concerts, and the like. You can import them into your personal calendar in various calendar apps and programs, though when you do it in this manner it is only a one-time import which does not automatically update to reflect changes in the event as subscribable calendars do.

Contents

Subscribing to calendars

These system-specific methods are always subject to change as new versions of the respective software are released.

Apple iOS (iPhone, iPad, etc.)

Open the Settings app, and go to Mail, Contacts and Calendars. Pick Add Account... and then Other, and Add Subscribed Calendar. It then asks for the "Server", and here's where you type or paste in the calendar URL. The calendar will now show up among your other calendars in the Calendar app, color-coded to distinguish it.

Apple OSX Calendar (Mac)

In the File menu, pick New Calendar Subscription. Enter the URL of the calendar. You'll get one more screen to set various characteristics of the subscription.

Google Calendar

Click on the arrow to the right of "Other Calendars" in the left column to bring up a pulldown menu. Select Add by URL. Type or paste in the calendar URL.

Microsoft Outlook

Click on Open Calendar (in top button row), and pick "From Internet". Enter the URL of the calendar and click "Yes" on the next screen to confirm adding it. Cross your fingers that it will work, since Microsoft can have quirky ideas of how to implement standards.

Mozilla Sunbird

Pick Subscribe to Remote Calendar from File menu. Choose "On the Network", then "iCalendar (ICS)". Enter the URL in the Location field. You can give the calendar a nickname and color on the next screen.

Specs and standards

Sample files

APIs

Programs and utilities

Other links

Personal tools
Namespaces

Variants
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