Sustainability of Digital Formats: Planning for Library of Congress Collections

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HTML Electronic Calendar and Scheduling Format

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name HTML Electronic Calendar and Scheduling Format

The hCalendar microformat is a 1:1 representation of iCal's VEVENT properties and values in semantic HTML using HTML classes and rel attributes. hCalendar events can be embedded directly in web pages. In addition, hCalendar enables applications to retrieve information about such events directly from web pages without having to reference a separate file.

See Notes for description of the file structure.

Relationship to other formats
    Subtype of iCal, iCalendar Electronic Calendar and Scheduling Format
    Contains Geo (Microformat). Microformat used to include the coordinates of the event's location within an hCalendar event. Not documented at this time.

Local use Explanation of format description terms

LC experience or existing holdings The Library of Congress has a small amount of fCal files in its collections.
LC preference The Library of Congress has not yet specified a format preference for calendars.  See the Library of Congress Recommended Formats Statement for format preferences for email which is often associated with calendaring applications.

Sustainability factors Explanation of format description terms


Open specification available from


hCalendar is based on iCal which is fully documented though RFC 5545, RFC 2446, and RFC 2447. Additional documentation available through also publishes the hCalendar XMDP profile which defines some of the class attribute values (class names) and their meanings according to the semantics defined in the hCalendar specification.


Strong adoption. lists examples of use including Wikipedia, Facebook, Yahoo!Local, University of Oxford (UK) and SubPop records. Comments welcome.

    Licensing and patents This specification is subject to a royalty free patent policy, e.g. per the W3C Patent Policy, and IETF RFC 3667 and RFC 3668.

According to the original definition, "designed for humans first and machines second, microformats are a set of simple, open data formats built upon existing and widely adopted standards."


hCalendar features well-defined metadata. See iCal for syntax details.

External dependencies


Technical protection considerations None

Quality and functionality factors Explanation of format description terms

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension html

Comments welcome.

Pronom PUID See note.  No corresponding match as of July 2023
Wikidata Title ID Q306432

Notes Explanation of format description terms


The basic format of hCalendar is to use iCal object/property names in lower-case for class names, and to map the nesting of iCal objects directly into nested XHTML elements. As detailed in RFC 5545, VEVENT defines the iCal calendar component and is required for each event listing. Within vevent, two properties are required for hCalendar: dtstart (DATE-TIME when calendar component begins expressed in ISO 8601 format) and summary (short summary or subject for the calendar component). Optional properties include location, url, dtend, duration (ISO date duration), rdate, rrule, category, description, uid, geo (latitude, longitude), attendee (partstat, role), contact, organizer, attach, and status. This list is still under development. One compatibility issue with hCalendar to iCal conversation is with the dtend property. The iCal specification expects dtend to record the day after the the last day of a multi-day event (a.k.a an exclusive end date) but hCalendar acknowledges that many users typically publish the end date of a multi-day event as the last day the event occurs (an inclusive end data). To compensate, hCalendar to iCalendar converters must automatically convert such inclusive hCalendar end date (dtend) property values to the equivalent exclusive iCalendar DTEND property values.


The hCalendar microformat was initiated on 2005-06-20 at the Supernova Conference in San Francisco, CA.

Format specifications Explanation of format description terms

Useful references


Last Updated: 07/20/2023