.ifb File Extension

What kind of file is an .ifb?

An .ifb file contains iCalendar free/busy information. It uses the registered text/calendar MIME type, like an .ics file, but the suffix specifically signals availability data rather than an arbitrary set of calendar components.¹

IFB is structured UTF-8 text, not a binary format. It has no magic number. A conforming file is wrapped in BEGIN:VCALENDAR and END:VCALENDAR, while each availability object uses BEGIN:VFREEBUSY and END:VFREEBUSY. The FREEBUSY properties describe periods as UTC start/end pairs or start/duration pairs.¹²

How do I open an .ifb on my computer?

For inspection, open the file in a UTF-8 text editor such as Visual Studio Code, Notepad, TextEdit, or Vim. This works on Windows, macOS, and Linux. Mobile text editors can display it too.

Use iCalendar-aware scheduling software or a standards-compliant library when you need to interpret the periods. Consumer calendar apps commonly associate themselves with .ics, but may not register .ifb or display a standalone VFREEBUSY object as events. If an app only accepts .ics, renaming a copy may let it recognize the same iCalendar text, but it does not convert the content or guarantee that the app supports free/busy objects.

An IFB file can represent a request, a reply, or published busy time. RFC 5546 defines the corresponding REQUEST, REPLY, and PUBLISH scheduling methods.³ Use the software or service that produced the file when you need to preserve that transaction context.

Poly support for .ifb

Poly can store, sync, share, version, download, and find .ifb files by name. Poly does not currently infer text/calendar from this suffix alone. When the correct MIME type is supplied, Poly opens the readable source in its text editor and indexes it for exact and meaning-based search.

The Poly agent can read stated organizers, attendees, time windows, comments, and FREEBUSY periods in correctly classified files. Poly does not render an availability grid, contact a calendar server, or calculate new availability from event collections. Confirm scheduling decisions in a calendar system that understands the complete exchange.

History of .ifb

The IETF Calendaring and Scheduling Working Group introduced iCalendar and the .ifb convention in RFC 2445 in November 1998.⁴ RFC 5545 replaced that specification in September 2009 while retaining iCalendar version 2.0 and the dedicated extension for free or busy time information.¹²

The name is a compact abbreviation of iCalendar free/busy. RFC 5545 permits multiple VFREEBUSY components in one calendar object, such as monthly groups. It does not permit recurrence rules inside them. Recurring events must already be expanded into individual FREEBUSY periods.²

Working with .ifb and alternatives

Use a calendar-aware parser for conversion. Preserve UTC timestamps, FBTYPE values such as BUSY-TENTATIVE and BUSY-UNAVAILABLE, and the requested time window. Sorting periods by start and end time is recommended, but overlapping or adjacent periods may still require application-specific normalization.²

Availability is privacy-sensitive even when event titles are absent. Patterns can reveal working hours, travel, appointments, and absences; the file may also contain email addresses, comments, or URLs. Review the source, restrict access, and use protected transport for sensitive schedules.