`.ics` File Extension

Learn what an .ics file contains, how to open or import iCalendar events, how Poly supports ICS files, and when to use another format.

File extension details for `.ics`

Partial Support

File type	iCalendar calendar and scheduling file
MIME type	`text/calendar`
Encoding	UTF-8 text with CRLF-delimited iCalendar content lines
Operating systems	Windows, macOS, Linux, iOS, Android
Opens with	Apple Calendar, Google Calendar, Microsoft Outlook, Mozilla Thunderbird
Poly support	Yes. Poly recognizes ICS calendar files and supports source preview, search, and agent use.
Indexed by Poly	Yes. Poly indexes readable iCalendar source for exact and semantic search.
Preview in Poly	Partial. ICS files open as source text, not as a calendar or event form.
Poly agent	Yes. The Poly agent can read stated events and fields without expanding them into normalized calendar entries.

What kind of file is an `.ics`?

An .ics file contains iCalendar data for exchanging events, tasks, journal entries, free/busy information, alarms, and time-zone definitions. It normally uses the text/calendar MIME type. The format is an open IETF standard, not an Apple-only file type or a calendar service.¹

ICS is structured UTF-8 text rather than binary data. There is no registered magic number. A normal file starts with BEGIN:VCALENDAR, includes VERSION:2.0, and ends with END:VCALENDAR. Those lines are useful content checks, but a calendar parser must still validate the complete file.¹²

Renaming a text file to .ics does not make it a valid calendar. Likewise, renaming an .ics file to .csv does not convert its events into rows.

How do I open an `.ics` on my computer?

Use a calendar application when you want to view or add its events:

On macOS, iPhone, and iPad, Apple Calendar imports ICS files. Calendar on Mac can also export them.³
On Windows or the web, Microsoft Outlook can import an ICS file. Outlook also supports subscribing to a published calendar URL.⁴
Google Calendar imports ICS files through its settings.⁵
On Linux, Mozilla Thunderbird and other iCalendar-aware applications can open or import them.

Importing copies the events currently in the file. Subscribing to a calendar URL allows the application to fetch later changes. Microsoft notes that an imported calendar does not refresh automatically, while a subscribed calendar does.⁴

Poly support for `.ics`

Poly opens an ICS file in its text editor and indexes its readable source for exact and meaning-based search. Event titles, descriptions, locations, attendees, dates, and recurrence fields can be found, and the Poly agent can reason about the stated calendar data.

The preview is source-oriented. Poly does not render a calendar grid, expand an RRULE into every occurrence, resolve every time zone for display, or import each VEVENT as a separate calendar object. Confirm complex recurrence and ambiguous local times in a calendar application.

History of `.ics`

The IETF Calendaring and Scheduling Working Group introduced iCalendar in RFC 2445 in November 1998. Frank Dawson of Lotus and Derik Stenerson of Microsoft edited that specification, building heavily on the earlier vCalendar industry format.⁶

RFC 5545 replaced it in September 2009 while retaining VERSION:2.0. IANA registers .ics for arbitrary calendar and scheduling information and .ifb specifically for free/busy information.¹²

Working with `.ics` and alternatives

iCalendar preserves calendar semantics that a flat table cannot represent cleanly. Choose the destination according to the job:

Format	Best for	Main tradeoff
ICS	Calendar exchange, recurrence, time zones, attendees, and alarms	Application support for extensions can vary
CSV	Simple event lists and spreadsheet analysis	Recurrence, alarms, and time zones need custom handling
JSON	Application-specific APIs	No single universal iCalendar-to-JSON mapping
PDF	A fixed, printable schedule	Cannot be imported as a live calendar

Use a calendar-aware exporter or library for conversion. iCalendar content lines use CRLF endings and should be folded after 75 octets, with continuation lines beginning with a space or tab.² Hand edits can break escaping, recurrence rules, or time-zone references.

Calendar files may reveal attendee addresses, locations, conference links, travel plans, and availability. CLASS:PRIVATE is metadata, not encryption. Inspect unexpected invitations and external links, share sensitive files through an appropriately protected channel, and keep the original before converting.

Internet Assigned Numbers Authority. text/calendar Media Type Registration. The registration lists .ics, .ifb, UTF-8, and the absence of a magic number. ↩ ↩² ↩³
Internet Engineering Task Force. RFC 5545: Internet Calendaring and Scheduling Core Object Specification (iCalendar). ↩ ↩² ↩³
Apple Support. Import or export calendars on Mac. ↩
Microsoft Support. Import or subscribe to a calendar in Outlook.com or Outlook on the web. ↩ ↩²
Google Calendar Help. Import events to Google Calendar. ↩
Internet Engineering Task Force. RFC 2445: Internet Calendaring and Scheduling Core Object Specification (iCalendar). ↩

.ics File Extension

File extension details for .ics

What kind of file is an .ics?

How do I open an .ics on my computer?

Poly support for .ics

History of .ics

Working with .ics and alternatives

Footnotes