The short answer
- iCalendar is a text calendar format that exchanges events, tasks, journal entries and free/busy information, but importing an ICS file does not establish ongoing synchronization.
- To inspect an ICS or IFB file, open it in a local text editor. To add ICS events on a Windows or Mac computer, open Google Calendar in a browser, go to Settings → Import & Export, select the .ics file, choose the destination calendar and click Import. Google's documented import workflow requires a computer; use that workflow for a file received on your phone.
- Treat unfamiliar ICS invitations cautiously. VALARM reminders can cause disruption; email reminders may expose location information or send spam. RFC 9074 recommends removing third-party VALARM components before storage in receiving CalDAV clients and servers. The format itself does not secure transmission. See [RFC 9074, section 9](https://www.rfc-editor.org/rfc/rfc9074.html#section-9).
Open ICS and IFB iCalendar files
ICS stores calendar and scheduling information; IFB is the extension for free/busy information. The registered media type is text/calendar, with no defined magic number. Calendar text is enclosed by BEGIN:VCALENDAR and END:VCALENDAR; events use VEVENT. See the [IANA registration](https://www.iana.org/assignments/media-types/text/calendar).
Do not assume an ICS-to-CSV transfer preserves everything. Google Calendar omits guests and conference data during event import, and recurring events imported through CSV may become separate events. Keep the original and compare the result. Renaming .ics to .csv does not convert the contents. See [Google's import guidance](https://support.google.com/calendar/answer/37118?hl=en).
How to open it
To inspect an ICS or IFB file, open it in a local text editor. To add ICS events on a Windows or Mac computer, open Google Calendar in a browser, go to Settings → Import & Export, select the .ics file, choose the destination calendar and click Import. Google's documented import workflow requires a computer; use that workflow for a file received on your phone.
To inspect an ICS or IFB file, open it in a local text editor. To add ICS events on a Windows or Mac computer, open Google Calendar in a browser, go to Settings → Import & Export, select the .ics file, choose the destination calendar and click Import. Google's documented import workflow requires a computer; use that workflow for a file received on your phone.
Do not assume an ICS-to-CSV transfer preserves everything. Google Calendar omits guests and conference data during event import, and recurring events imported through CSV may become separate events. Keep the original and compare the result. Renaming .ics to .csv does not convert the contents. See [Google's import guidance](https://support.google.com/calendar/answer/37118?hl=en).
File safety
Treat unfamiliar ICS invitations cautiously. VALARM reminders can cause disruption; email reminders may expose location information or send spam. RFC 9074 recommends removing third-party VALARM components before storage in receiving CalDAV clients and servers. The format itself does not secure transmission. See [RFC 9074, section 9](https://www.rfc-editor.org/rfc/rfc9074.html#section-9).
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
Do not assume an ICS-to-CSV transfer preserves everything. Google Calendar omits guests and conference data during event import, and recurring events imported through CSV may become separate events. Keep the original and compare the result. Renaming .ics to .csv does not convert the contents. See [Google's import guidance](https://support.google.com/calendar/answer/37118?hl=en).
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is an ICS iCalendar file used for?
An ICS file exchanges calendar information such as events, tasks, journal entries and free/busy information independently of a particular calendar service.
How do I open an ICS file to read its contents?
Open it in a text editor. Look for BEGIN:VCALENDAR and END:VCALENDAR around the calendar data and VEVENT around event data.
How do I open an ICS file on Windows?
Use a local text editor to inspect it. To import events, open Google Calendar in a desktop browser and use Settings → Import & Export → Select file → Import.
How do I open an ICS file on Mac?
Use a text editor to read the file, or open Google Calendar in your computer's browser and select the ICS file under Settings → Import & Export.
How do I import an ICS file received on my phone?
Google documents ICS import on a computer. Make the file available on your computer, then select it in Google Calendar's Import & Export settings.
What is the difference between ICS and IFB files?
IANA assigns .ics to calendar and scheduling information and .ifb to free/busy information. Both use the text/calendar media type; choose according to the information you need to exchange.
Will converting ICS to CSV preserve recurring events?
Do not assume so. Google warns that recurring events imported through CSV may become separate events. Compare the recurrence pattern after conversion and import.
How do I troubleshoot garbled text in an ICS file?
Try opening the original in a text editor using UTF-8. The standard requires generated data to use UTF-8 and readers to accept UTF-8 or US-ASCII. Ask the sender for a fresh UTF-8 export if the text remains unreadable.
Why are guests missing after an ICS import into Google Calendar?
Google Calendar does not import guests or conference data with events. Their absence does not by itself mean the ICS file is damaged.
Are unknown ICS calendar invitations safe to import?
The extension alone does not establish trust. Check the sender and review reminders before importing; VALARM behavior can disrupt users, and email reminders may disclose location information or send spam.
Can I read an ICS file without uploading it?
You can inspect its text in a local text editor without importing it into an online calendar. Importing into Google Calendar adds the events to the chosen online calendar.
Why does an ICS import not sync later changes?
An import does not maintain synchronization between the source and destination accounts. Later source changes are not kept in sync by that import.
Related formats
Sources
RFC 5545: Internet Calendaring and Scheduling Core Object Specification (iCalendar) · IETF / RFC Editor
IANA Media Type Registration: text/calendar · IANA
Import events to Google Calendar · Google Calendar Help
RFC 9074: VALARM Extensions for iCalendar · IETF / RFC Editor