Calendaring extensions N. Jenkins
Internet-Draft R. Stepanek
Intended status: Standards Track FastMail
Expires: November 10, 2018 May 9, 2018

JSCalendar: A JSON representation of calendar data


This specification defines a data model and JSON representation of calendar data that can be used for storage and data exchange in a calendaring and scheduling environment. It aims to be an alternative to the widely deployed iCalendar data format and to be unambiguous, extendable and simple to process.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on November 10, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

1. Introduction

This document defines a data model for calendar event and task objects, or groups of such objects, in electronic calendar applications and systems. It aims to be unambiguous, extendable and simple to process.

The key design considerations for this data model are as follows:

The representation of this data model is defined in the I-JSON format [RFC7493], which is a strict subset of the JavaScript Object Notation (JSON) Data Interchange Format [RFC8259]. Using JSON mostly is a pragmatic choice: its widespread use should help to speed up JSCalendar adoption and a wide range of production-ready JSON implementations allows to decrease interoperability issues.

1.1. Relation to the iCalendar format

The iCalendar data format [RFC5545], a widely deployed interchange format for calendaring and scheduling data, has served calendaring vendors for a long while, but contains some ambiguities and pitfalls that can not be overcome without backward-incompatible changes.

For example, iCalendar defines various formats for local times, UTC time and dates, which confuses new users. Other sources for errors are the requirement for custom time-zone definitions within a single calendar component, as well as the iCalendar format itself; the latter causing interoperability issues due to misuse of CR LF terminated strings, line continuations and subtle differences between iCalendar parsers. Lastly, up until recently the iCalendar format did not allow to express the difference between two calendar components, which results in verbose exchanges during scheduling.

Some of these issues were addressed by the jCal format, which is a direct mapping between iCalendar and JSON. However, it did not attempt to extend or update iCalendar semantics.

1.2. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

The underlying format used for this specification is JSON. Consequently, the terms "object" and "array" as well as the four primitive types (strings, numbers, booleans, and null) are to be interpreted as described in Section 1 of[RFC8259].

Some examples in this document contain "partial" JSON documents used for illustrative purposes. In these examples, three periods "..." are used to indicate a portion of the document that has been removed for compactness.

2. JSCalendar objects

This section describes the calendar object types specified by JSCalendar.

2.1. JSEvent

MIME type: application/calendar+json;type=jsevent

A JSEvent represents a scheduled amount of time on a calendar, typically a meeting, appointment, reminder or anniversary. Multiple participants may partake in the event at multiple locations.

The @type property value MUST be jsevent.

2.2. JSTask

MIME type: application/calendar+json;type=jstask

A JSTask represents an action-item, assignment, to-do or work item .

The @type property value MUST be jstask.

A JSTask may start and be due at certain points in time, may take some estimated time to complete and may recur; none of which is required. This notably differs from JSEvent which is required to start at a certain point in time and typically takes some non-zero duration to complete.

2.3. JSGroup

MIME type: application/calendar+json;type=jsgroup

A JSGroup is a collection of JSEvent and JSTask objects. Typically, objects are grouped by topic (e.g. by keywords) or calendar membership.

The @type property value MUST be jsgroup.

3. Structure of JSCalendar objects

A JSCalendar object is a JSON object, which MUST be valid I-JSON (a stricter subset of JSON), as specified in [RFC8259]. Property names and values are case-sensitive.

The object has a collection of properties, as specified in the following sections. Unless otherwise specified, all properties are optional; omitted properties MUST be treated identically to if that property had the value of null, unless otherwise specified.

3.1. Type signatures

Types signatures are given for all JSON objects in this document. The following conventions are used:

3.2. Data Types

In addition to the standard JSON data types, the following data types are used in this specification:

3.2.1. UTCDate

This is a string in [RFC3339] date-time format, with the further restrictions that any letters MUST be in upper-case, the time component MUST be included and the time MUST be in UTC. Fractional second values MUST NOT be included unless non-zero and MUST NOT have trailing zeros, to ensure there is only a single representation for each date-time.

For example 2010-10-10T10:10:10.003Z is OK, but 2010-10-10T10:10:10.000Z is invalid and MUST be encoded as 2010-10-10T10:10:10Z.

In common notation, it should be of the form YYYY-MM-DDTHH:MM:SSZ.

3.2.2. LocalDate

This is a date-time string with no time-zone/offset information. It is otherwise in the same format as UTCDate: YYYY-MM-DDTHH:MM:SS. The time-zone to associate the LocalDate with comes from an associated property, or if no time-zone is associated it defines floating time. Floating date-times are not tied to any specific time-zone. Instead, they occur in every timezone at the same wall-clock time (as opposed to the same instant point in time).

3.2.3. Duration

A duration is represented by a subset of ISO8601 duration format, as specified by the following ABNF:

    dur-secfrac = "." 1*DIGIT
    dur-second  = 1*DIGIT [dur-secfrac] "S"
    dur-minute  = 1*DIGIT "M" [dur-second]
    dur-hour    = 1*DIGIT "H" [dur-minute]
    dur-time    = "T" (dur-hour / dur-minute / dur-second)
    dur-day     = 1*DIGIT "D"

    duration    = "P" (dur-day [dur-time] / dur-time)

In addition, the duration MUST NOT include fractional second values unless the fraction is non-zero. A zero duration MUST be represented as P0D.

3.2.4. PatchObject

A PatchObject is of type String[*|null], and represents an unordered set of patches on a JSON object. The keys are a path in a subset of [RFC6901] JSON pointer format, with an implicit leading / (i.e. prefix each key with / before applying the JSON pointer evaluation algorithm).

A patch within a PatchObject is only valid, if all of the following conditions apply:

  1. The pointer MUST NOT reference inside an array (i.e. it MUST NOT insert/delete from an array; the array MUST be replaced in its entirety instead).
  2. When evaluating a path, all parts prior to the last (i.e. the value after the final slash) MUST exist.
  3. There MUST NOT be two patches in the PatchObject where the pointer of one is the prefix of the pointer of the other, e.g. alerts/1/offset and alerts.

The value associated with each pointer is either:

Implementations MUST reject a PatchObject if any of its patches are invalid.

3.2.5. Identifiers

If not noted otherwise, properties that define identifiers MUST be string values, MUST be at least 1 character in length and maximum 256 octets in size, and MUST only contain characters from the “URL and Filename safe” Base 64 Alphabet, as defined in section 5 of [RFC4648]. This is the ASCII alphanumeric characters (A-Za-z0-9), hyphen (-), and underscore (_).

3.2.6. Normalisation and equivalence

JSCalendar aims to provide unambiguous definitions for value types and properties, but does not define a general normalisation or equivalence method for JSCalendar objects and types. This is because the notion of equivalence might range from byte-level equivalence to semantic equivalence, depending on the respective use case (for example, the CalDAV protocol [RFC4791] requires octet equivalence of the encoded calendar object to determine ETag equivalence).

Normalisation of JSCalendar objects is hindered because of the following reasons:

Considering this, the definition of equivalence and normalisation is left to client and server implementations and to be negotiated by a calendar exchange protocol or defined by another RFC.

3.3. Custom property extensions and values

Vendors MAY add additional properties to the calendar object to support their custom features. The names of these properties MUST be prefixed with a domain name controlled by the vendor to avoid conflict, e.g.

Some JSCalendar properties allow vendor-specific value extensions. If so, vendor specific values MUST be prefixed with a domain name controlled by the vendor, e.g., unless otherwise noted.

4. Common JSCalendar properties

This section describes the properties that are common to the various JSCalendar object types. Specific JSCalendar object types may only support a subset of these properties. The object type definitions in section Section 5 describe the set of supported properties per type.

4.1. Metadata properties

4.1.1. @type

Type: String

Specifies the type which this object represents. This MUST be one of the following values, registered in a future RFC, or a vendor-specific value:

A valid JSCalendar object MUST include this property.

4.1.2. uid

Type: String

A globally unique identifier, used to associate the object as the same across different systems, calendars and views. The value of this property MUST be unique across all JSCalendar objects, even if they are of different type. [RFC4122] describes a range of established algorithms to generate universally unique identifiers (UUID), and the random or pseudo-random version is recommended to use.

For compatibility with [RFC5545] UIDs, implementations MUST be able to receive and persist values of at least 255 octets for this property, but they MUST NOT truncate values in the middle of a UTF-8 multi-octet sequence.

A valid JSCalendar object MUST include this property.

4.1.3. relatedTo

Type: String[Relation]|null

Relates the object to other JSCalendar objects. This is represented as a map of the uids of the related objects to information about the relation.

A Relation object has the following properties:

If an object is split to make a "this and future" change to a recurrence, the original object MUST be truncated to end at the previous occurrence before this split, and a new object created to represent all the objects after the split. A relation=["next"] relatedTo property MUST be set on the original object with the uid of the new object. A relation=["first"] relatedTo property with the UID of the first object in the series MUST be set on the new object. Clients can then follow these UIDs to get the complete set of objects if the user wishes to modify them all at once.

4.1.4. prodId

Type: String|null

The identifier for the product that created the JSCalendar object.

The vendor of the implementation SHOULD ensure that this is a globally unique identifier, using some technique such as an FPI value, as defined in [ISO.9070.1991]. It MUST only use characters of an iCalendar TEXT data value (see section 3.3.11 in [RFC5545]).

This property SHOULD NOT be used to alter the interpretation of an JSCalendar object beyond the semantics specified in this document. For example, it is not to be used to further the understanding of non-standard properties.

4.1.5. created

Type: UTCDate|null

The date and time this object was initially created.

4.1.6. updated

Type: UTCDate

The date and time the data in this object was last modified.

4.1.7. sequence

Type: Number (Defaults to 0 if omitted)

Initially zero, this MUST be a non-negative integer that is monotonically incremented each time a change is made to the object.

4.1.8. method

Type: String|null

The iTIP ([RFC5546]) method, in lower-case. Used for scheduling.

4.2. What and where properties

4.2.1. title

Type: String (Defaults to the empty string if omitted)

A short summary of the object.

4.2.2. description

Type: String (Defaults to the empty string if omitted)

A longer form description of the object. This is plain text, but a client SHOULD attempt to hyperlink URLs when displaying it.

4.2.3. htmlDescription

Type: String|null (Defaults to null if omitted)

A longer form rich-text description of the object. This is HTML text and allows to reference resources in the links property by use of CID URLs (see [RFC2392]). To convert a CID URL to the cid property value of a Link object, implementations MUST follow the conversion described in section 2 of [RFC2392]. Implementations MAY choose not to follow untrusted external CID URLs referenced in the links property, in which case they MUST treat the htmlDescription property as if omitted. Implementations MUST preserve the value of this property, even if it contains untrusted links.

4.2.4. locations

Type: String[Location]|null

A map of location ids to Location objects, representing locations associated with the object. A location id may be any valid [RFC6901] JSON pointer and need only be unique to this object; a UUID is a practical choice.

A Location object has the following properties. All properties are optional, but every Location object MUST have at least one property:

4.2.5. links

Type: String[Link]|null

A map of link ids to Link objects, representing external resources associated with the object. A link id may be any valid [RFC6901] JSON pointer and need only be unique to this object; the href or a UUID are practical choices.

A Link object has the following properties:

4.2.6. locale

Type: String|null

The [RFC5646] language tag that best describes the locale used for the calendar object, if known.

4.2.7. keywords

Type: String[]|null

A list of keywords or tags related to the object. The values are free-form and do not have to follow any particular structure.

4.2.8. categories

Type: String[]|null

Specifies the categories related to the calendar object. Array values MUST be URIs. In contrast to keywords, categories typically are structured.

For example, a vendor owning the domain might define the categories" and

4.2.9. color

Type: String|null

Specifies a color clients MAY use when displaying this calendar object. The value is a case-insensitive color name taken from the CSS3 set of names, defined in Section 4.3 of W3C.REC-css3-color-20110607 or a CSS3 RGB color hex value.

4.3. Recurrence properties

4.3.1. recurrenceRule

Type: Recurrence

Defines a recurrence rule (repeating pattern) for recurring calendar objects.

A Recurrence object is a JSON object mapping of a RECUR value type in iCalendar, see [RFC5545] and[RFC7529]. Objects recur by applying the recurrence rule (and recurrenceOverrides) to the start date/time. A JSTask without a start property value recurs by its due date/time, if defined.

A Recurrence object has the following properties:

4.3.2. recurrenceOverrides

Type: LocalDate[PatchObject|null]|null

A map of the recurrence-ids (the date-time of the start of the occurrence) to either null, to indicate the occurrence should be deleted, or an object of patches to apply to the generated occurrence object.

If the recurrence-id does not match an expanded start date from a recurrence rule, it is to be treated as an additional occurrence (like an RDATE from iCalendar). The patch object may often be empty in this case.

By default, an occurrence inherits all properties from the main object except the start (or due) date-time, which is shifted to the new start time. However, individual properties of the occurrence can be modified by a patch, or multiple patches.

A pointer in the PatchObject MUST NOT start with one of the following prefixes; any patch with such a key MUST be ignored:

4.4. Sharing and scheduling properties

4.4.1. priority

Type: Number(defaults to 0 if omitted)

Specifies a priority for the calendar object. This may be used as part of scheduling systems to help resolve conflicts for a time period.

The priority is specified as an integer in the range 0 to 9. A value of 0 specifies an undefined priority. A value of 1 is the highest priority. A value of 2 is the second highest priority. Subsequent numbers specify a decreasing ordinal priority. A value of 9 is the lowest priority. Other integer values are reserved for future use.

4.4.2. freeBusyStatus

Type: String(defaults to busy if omitted)

Specifies how this property should be treated when calculating free-busy state. The value MUST be one of:

4.4.3. privacy

Type: String(defaults to public if omitted)

Calendar objects are normally collected together and may be shared with other users. The privacy property allows the object owner to indicate that it should not be shared, or should only have the time information shared but the details withheld. Enforcement of the restrictions indicated by this property are up to the implementations.

This property MUST NOT affect the information sent to scheduled participants; it is only interpreted when the object is shared as part of a shared calendar.

The value MUST be either one of the following values, registered in a future RFC, or a vendor-specific value. Vendor specific values MUST be prefixed with a domain name controlled by the vendor, e.g. Any value the client or server doesn't understand should be preserved but treated as equivalent to private.

4.4.4. replyTo

Type: String[String]|null

Represents methods by which a participant may RSVP to the organizer of the calendar object. The keys in the property value are the available methods. The value is a URI to use that method. Future methods may be defined in future specifications; a calendar client MUST ignore any method it does not understand.

The following methods are defined:

replyTo URI Template variables
Variable Expand to
email The email property value of the replying Participant object.
uid The uid property value of the JSCalendar object.
sequence The sequence property value of the JSCalendar object.
recurrenceId The recurrence-id when replying for a single occurrence of a recurring JSCalendar object. The value is the date-time of the non-overridden start as determined by expanding the recurrenceRule of the JSCalendar object.

4.4.5. participants

Type: String[Participant]|null

A map of participant ids to participants, describing their participation in the calendar object. A participant id may be any valid [RFC6901] JSON pointer and need only be unique to this calendar object; the email address of the participant is a good choice.

A Participant object has the following properties. Properties are mandatory unless marked otherwise:

4.5. Alerts properties

4.5.1. useDefaultAlerts

Type: Boolean (defaults to false if omitted)

If true, use the user's default alerts and ignore the value of the alerts property. Fetching user defaults is dependent on the API from which this JSCalendar object is being fetched, and is not defined in this specification. If an implementation cannot determine the user's default alerts, or none are set, it MUST process the alerts property as if useDefaultAlerts is set to false.

4.5.2. alerts

Type: String[Alert]|null

A map of alert ids to Alert objects, representing alerts/reminders to display or send the user for this calendar object. An alert id may be any valid [RFC6901] JSON pointer and need only be unique to this calendar object; a globally unique id is a practical choice (also see Section 4.1.2)).

An Alert Object has the following properties:

5. Type-specific JSCalendar properties

5.1. JSEvent properties

In addition to the common JSCalendar object properties a JSEvent has the following properties:

5.1.1. start

Type: LocalDate e.g. 2015-09-02T00:00:00

The date/time the event would start in the event's time-zone.

A valid JSEvent MUST include this property.

5.1.2. timeZone

Type: String|null

The IANA Time Zone Database name for the time-zone the event is scheduled in, or null for floating time. If omitted, this MUST be presumed to be null (i.e. floating time).

5.1.3. duration

Type: Duration, e.g. P2DT3H (Defaults to P0D if omitted)

The zero or positive duration of the event in absolute time (i.e. in UTC time; ignoring DST shifts). To get the end date in the event time-zone, convert start into UTC, then add the duration, then convert the result into the appropriate time-zone.

A JSEvent MAY be end in a different time-zone (e.g. a plane flight crossing time-zones). In this case, the JSEvent MUST specify the end time-zone in a location property value that defines its rel to be end and the end time-zone in its timeZone property.

5.1.4. isAllDay

Type: Boolean (optional, defaults to false)

Specifies if the event an all day event, such as a birthday or public holiday.

If isAllDay is true, then the following restrictions apply: timeZone property.

Note that all-day events MAY be bound to a specific time-zone, as defined by the

5.1.5. status

Type: String

The scheduling status (Section 4.4) of a JSEvent defaults to confirmed if omitted.

If set, it MUST be one of:

5.2. JSTask properties

In addition to the common JSCalendar object properties a JSTask has the following properties:

5.2.1. due

Type: LocalDate|null e.g. 2015-09-02T00:00:00

The date/time the task is due in the task's time-zone.

5.2.2. start

Type: LocalDate|null e.g. 2015-09-02T00:00:00

The date/time the task should start in the task's time-zone.

5.2.3. timeZone

Type: String|null

The IANA Time Zone Database name for the time-zone the task is scheduled in, or null for floating time. If omitted, this MUST be presumed to be null (i.e. floating time).

5.2.4. estimatedDuration

Type: Duration|null, e.g. P2DT3H

Specifies the estimated positive duration of time the task takes to complete.

If the start and due properties are set, the estimated duration SHOULD be less than or equal to the time interval between these properties.

5.2.5. completed

Type: UTCDate|null, e.g. 2016-06-13T12:00:00Z

Specifies the date/time the task was completed.

If the task is recurring and has future instances, a client may want to denote a specific task recurrence as completed but leave other instances as uncompleted. One way to achieve this is by overriding the completed property in the task recurrenceOverrides. However, this could produce a long list of completion times for regularly recurring tasks. An alternative approach is to split the JSTask into a current, single instance of JSTask with this instance completion time and a future recurring instance. Also see the definition of the relatedTo on splitting.

5.2.6. isAllDay

Type: Boolean (optional, defaults to false)

Specifies if the task is an all day task.

If isAllDay is true, then the start and due properties MUST have a time component of T00:00:00. Note that the estimatedDuration property MAY contain a non-zero time duration. All-day tasks MAY be bound to a specific time-zone, as defined by the timeZone property.

5.2.7. progress

In addition to the common properties of a Participant object (Section 4.4.5), a Participant within a JSTask supports the following property:

A ParticipantProgress object has the following properties:

5.2.8. status

Type: String

If omitted, the default scheduling status (Section 4.4) of a JSTask is defined as follows (in order of evaluation):

If set, it MUST be one of:

5.3. JSGroup properties

JSGroup supports the following JSCalendar properties:

as well as the following JSGroup-specific properties:

5.3.1. entries

Type: (JSTask|JSEvent)[]|null

A list of group members. The list MAY contain multiple object types and implementations MUST ignore entries of unknown type. The property value MUST either be null or the list MUST NOT be empty.

5.3.2. source

Type: String|null (optional, default is null)

The source from which updated versions of this group may be retrieved from. If the value is not null, it MUST be a URI.

6. Conversion from and to iCalendar

This section specifies which JSCalendar properties can be mapped from and to iCalendar format. Implementations SHOULD follow these conversion guidelines. Still, JSCalendar does not restrict itself to iCalendar and conversion between these two formats MAY be lossy.

6.1. JSEvent

The iCalendar counterpart to JSEvent is the VEVENT component type [RFC5545]. A VEVENT component that is a direct child of a VCALENDAR component is equivalent to a standalone JSEvent. A VEVENT component within a VEVENT maps to the entries of the JSEvent recurrenceOverrides property.

Translation between JSEvent and iCalendar
Property iCalendar counterpart
isAllDay True, if the type of the DTSTART property in iCalendar is DATE. When translating from JSCalendar the iCalendar DTSTART property is of DATE value type, if the isAllDay property is set to true and the timeZone property is null.
start Corresponds to the DTSTART property in iCalendar. Note that time-zone information is stored separately in JSEvent.
timeZone Corresponds to the TZID part of the DTSTART property in iCalendar. If the event has a different end time-zone to start time-zone, this should be added as a JSCalendar location with just a timeZone property and rel="end".
duration Corresponds to the DURATION or DSTART+DTEND properties in iCalendar.

6.2. JSTask

The iCalendar counterpart to JSTask is the VTODO component type [RFC5545]. A VTODO component that is a direct child of a VCALENDAR component is equivalent to a standalone JSTask. A VTODO component within a master VTODO maps to the entries of the JSTask recurrenceOverrides property.

Translation between JSTask and iCalendar
Property iCalendar counterpart
isAllDay True, if the type of the DTSTART property in iCalendar is DATE. When translating from JSCalendar the iCalendar DTSTART property is of DATE value type, if the isAllDay property is set to true and the timeZone property is null.
due Corresponds to the DUE and DTSTART+DURATION properties in iCalendar. When mapping iCalendar VTODOs with DTSTART+DURATION, the due date is the result of adding DURATION to DTSTART in the DTSTART time-zone.
start Corresponds to the DTSTART property in iCalendar.
timeZone Corresponds to the TZID part of the DTSTART/DUE properties in iCalendar. If the task has a different end time-zone to start or due time-zone, this should be added as a JSCalendar location with just a timeZone property and rel="end".
estimatedDuration Corresponds to the ESTIMATED-DURATION iCalendar property. NON-STANDARD: this property is currently non-standard, see [draft-apthorp-ical-tasks].
completed Maps to the COMPLETED iCalendar property.
progress Corresponds to the PARTSTAT and COMPLETED properties in iCalendar, including the currently non-standard definitions in [draft-apthorp-ical-tasks].
status Corresponds to the STATUS property in iCalendar, including the currently non-standard definitions in [draft-apthorp-ical-tasks].

6.3. JSGroup

A JSGroup converts to a iCalendar VCALENDAR containing VEVENT or VTODO components.

Translation between JSGroup and iCalendar
Property iCalendar counterpart
entries The VEVENT and VTODO components within a top-level VCALENDAR component.
source Corresponds to the SOURCE property in iCalendar.

6.4. Common properties

Translation between JSCalendar and iCalendar
Property iCalendar counterpart
alerts An Alert corresponds to the VALARM component in iCalendar, where the action is determined by the iCalendar ACTION property value (e.g., both DISPLAY and AUDIO actions map to a JSCalendar DisplayAction alert, and similarly for an iCalendar EMAIL). The relativeTo and offset properties corresponds to the iCalendar TRIGGER property. The attachments property of an EmailAction alert map to iCalendar ATTACH properties. For mapping mediaLinks, the iCalendar currently forbids to define ATTACH properties on VALARMs with DISPLAY action. Mapping this property is implementation-specific, but using X-ATTACH with the same semantics as ATTACH is a sane choice.
categories Corresponds to the STRUCTURED-CATEGORY property in iCalendar, see. NON-STANDARD: this property is currently non-standard, see [draft-ietf-calext-ical-relations].
color Corresponds to the COLOR property in iCalendar, as specified in [RFC7986].
created Corresponds to the CREATED property in iCalendar.
description Corresponds to the DESCRIPTION property in iCalendar.
htmlDescription Corresponds to the ALTREP parameter of the DESCRIPTION property (e.g. by setting ALTREP to a data:text/html URL containing the HTML text). Alternatively, use the STYLED-DESCRIPTION property. NON-STANDARD: the STYLED-DESCRIPTION property currently is non-standard, see [draft-ietf-calext-eventpub-extensions].
freeBusyStatus Corresponds to the TRANSP property in iCalendar.
keywords Corresponds to the CATEGORIES property in iCalendar, as specified in [RFC7986].
links Corresponds to the ATTACH ([RFC5545]) or IMAGE ([RFC7986]) properties with a URI value type set to the link href. ([RFC7986]). The type property corresponds to the FMTTYPE parameter, the size property to the SIZE parameter. Mapping all other properties is implementation-specific.
locale Corresponds to the LANGUAGE parameter in iCalendar, which is added to individual properties. When converting from iCalendar, one language must be picked as the main locale.
locations See Section 6.5.
method Corresponds to the METHOD property in iCalendar.
participants See Section 6.5.
priority Corresponds to the PRIORITY property in iCalendar.
privacy Corresponds to the CLASS property in iCalendar.
prodId Corresponds to the PRODID property in iCalendar.
recurrenceOverrides Corresponds to the RDATE and EXDATE properties in iCalendar, plus VEVENT (for JSEvent) or VTODO (for JSTask) instances with a recurrence-id.
recurrenceRule Corresponds to the RRULE property in iCalendar. See the property definition at section Section 4.3.1 how to map a RRULE value.
relatedTo Corresponds to the RELATED-TO property in iCalendar.
replyTo An iCalendar ORGANIZER with one of the mapped URIs as value. If URIs are defined for both the imip and web type, it is recommended to map the imip value to the calendar address value of the ORGANIZER.
sequence Corresponds to the SEQUENCE property in iCalendar.
status Corresponds to the STATUS property in iCalendar (converted to lower-case).
title Corresponds to the SUMMARY property in iCalendar.
uid Corresponds to the UID property in iCalendar.
updated Corresponds to the DTSTAMP and LAST-MODIFIED properties in iCalendar. (These are only different in the iTIP case, and the difference is not actually useful.)

6.5. Locations and participants

Both JSCalendar participants and locations have counterparts in iCalendar but provide richer representation.

The following table outlines translation of JSCalendar participants. Where iCalendar has distinct properties for ORGANIZER and ATTENDEE, these are merged in JSCalendar into the Participant object type.

Translation of Participant between JSCalendar and iCalendar
Property iCalendar counterpart
delegatedFrom the DELEGATED-FROM parameter
delegatedTo email
the value of the ORGANIZER or ATTENDEE property kind
the CUTYPE parameter linkIds
Implementation-specific. locationId
Implementation-specific. When mapping from iCalendar to JSCalendar this may be the JSCalendar identifier of a CONFERENCE property that has the MODERATOR feature defined in its FEATURE parameter values. If multiple such CONFERENCE properties are defined in iCalendar, then the one with the most interactive features is chosen. memberOf
the MEMBER parameter name
the CN parameter participation
Maps to the standard iCalendar ROLE parameter values REQ-PARTICIPANT, OPT-PARTICIPANT and NON-PARTICIPANT. roles
The chair role maps to the standard iCalendar ROLE parameter value chair, with an implicit participant of value required. The mapping of non-required chairs and other roles is implementation-specific, but using x-name parameter values is recommended. rsvpResponse
the PARTSTAT parameter the DELEGATED-TO parameter
scheduleSequence the SEQUENCE property of the participant's latest iMIP message
scheduleUpdated the DTSTAMP property of the participant's latest iMIP message

For JSCalendar locations, the iCalendar counterparts are the [RFC5545] LOCATION and the extended iCalendar [RFC7986] CONFERENCE properties. Generally, use a LOCATION property if only the name property is set, CONFERENCE otherwise. For backwards compatibility with client implementations that do not support the CONFERENCE property, it is recommended to set use at least one LOCATION property, if the JSCalendar object contains locations.

Translation of Location between JSCalendar and iCalendar
Property iCalendar counterpart
name For LOCATION: corresponds to the property value. For CONFERENCE: corresponds to the LABEL parameter.
description Implementation-specific.
rel For CONFERENCE: implicitly virtual. Implementation-specific for LOCATION.
features For CONFERENCE: corresponds to the FEATURE parameter. Implementation-specific for LOCATION.
timeZone Implementation-specific.
coordinates Implementation-specific. Consider using a GEO iCalendar property, along with one LOCATION or CONFERENCE.
uri For LOCATION: corresponds to the ALTREP parameter. For CONFERENCE: corresponds to the property value.
linkIds Implementation-specific.

6.6. Unknown properties

Both JSCalendar and iCalendar calendar objects may contain properties that are not expressible in the other format. This specification does not mandate how to preserve these properties. Instead, it leaves negotiation on how to treat unknown properties to client and server implementations and their protocol used to exchange calendar objects.

Two notable options to represent and preserve arbitrary iCalendar object properties in JSCalendar are:

7. JSCalendar object examples

The following examples illustrate several aspects of the JSCalendar data model and format. The examples may omit mandatory or additional properties, which is indicated by a placeholder property with key .... While most of the examples use calendar event objects, they are also illustrative for tasks.

7.1. Simple event

This example illustrates a simple one-time event. It specifies a one-time event that begins on January 15, 2018 at 1pm New York local time and ends after 1 hour.

  "@type": "jsevent",
  "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f1",
  "updated": "2018-01-15T18:00:00Z",
  "title": "Some event",
  "start": "2018-01-15T13:00:00",
  "timeZone": "America/New_York",
  "duration": "PT1H"

7.2. Simple task

This example illustrates a simple task for a plain to-do item.

  "@type": "jstask",
  "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
  "updated": "2018-01-15T18:00:00Z",
  "title": "Do something"

7.3. Simple group

This example illustrates a simple calendar object group that contains an event and a task.

  "@type": "jsgroup",
  "uid": "2a358cee-6489-4f14-a57f-c104db4dc343",
  "updated": "2018-01-15T18:00:00Z",
  "name": "A simple group",
  "entries": [
      "@type": "jsevent",
      "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f1",
      "updated": "2018-01-15T18:00:00Z",
      "title": "Some event",
      "start": "2018-01-15T13:00:00",
      "timeZone": "America/New_York",
      "duration": "PT1H"
      "@type": "jstask",
      "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
      "updated": "2018-01-15T18:00:00Z",
      "title": "Do something"

7.4. All-day event

This example illustrates an event for an international holiday. It specifies an all-day event on April 1 that occurs every year since the year 1900.

  "...": "",
  "title": "April Fool's Day",
  "isAllDay": true,
  "start": "1900-04-01T00:00:00",
  "duration": "P1D",
  "recurrenceRule": {
    "frequency": "yearly"

7.5. Task with a due date

This example illustrates a task with a due date. It is a reminder to buy groceries before 6pm Vienna local time on January 19, 2018. The calendar user expects to need 1 hour for shopping.

  "...": "",
  "title": "Buy groceries",
  "due": "2018-01-19T18:00:00",
  "timeZone": "Europe/Vienna",
  "estimatedDuration": "PT1H"

7.6. Event with end time-zone

This example illustrates the use of end time-zones by use of an international flight. The flight starts on April 1, 2018 at 9am in Berlin local time. The duration of the flight is scheduled at 10 hours 30 minutes. The time at the flights destination is in the same time-zone as Tokyo. Calendar clients could use the end time-zone to display the arrival time in Tokyo local time and highlight the time-zone difference of the flight.

  "...": "",
  "title": "Flight XY51 from FRA to NRT",
  "start": "2018-04-01T09:00:00",
  "timeZone": "Europe/Berlin",
  "duration": "PT10H30M",
  "locations": {
    "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
      "rel": "end",
      "timeZone": "Asia/Tokyo"

7.7. Floating-time event (with recurrence)

This example illustrates the use of floating-time. Since January 1, 2018, a calendar user blocks 30 minutes every day to practice Yoga at 7am local time, in whatever time-zone the user is located on that date.

  "...": "",
  "title": "Yoga",
  "start": "2018-01-01T07:00:00",
  "duration": "PT30M",
  "recurrenceRule": {
    "frequency": "daily"

7.8. Event with multiple locations

This example illustrates an event that happens at both a physical and a virtual location. Fans can see a live convert on premises or online.

  "...": "",
  "title": "Live from Music Bowl: The Band",
  "description": "Go see the biggest music event ever!",
  "locale": "en",
  "start": "2018-07-04T17:00:00",
  "timeZone": "America/New_York",
  "duration": "PT3H",
  "locations": {
    "9366e041-bb4c-4aa4-b249-b4657cab925c": {
      "name": "The Music Bowl",
      "description": "Music Bowl, Central Park, New York",
      "coordinates": "geo:40.7829,73.9654"
    "6f3696c6-1e07-47d0-9ce1-f50014b0041a": {
      "name": "Free live Stream from Music Bowl",
      "rel": "virtual",
      "features": [
      "uri": ""

7.9. Recurring event with overrides

This example illustrates the use of recurrence overrides. A math course at a University is held for the first time on January 8, 2018 at 9am London time and occurs every week until June 25, 2018. Each lecture lasts for one hour and 30 minutes and is located at the Mathematics department. This event has exceptional occurrences: at the last occurrence of the course is an exam, which lasts for 2 hours and starts at 10am. Also, the location of the exam differs from the usual location. On April 2, May 7 and May 28 no course is held.

  "...": "",
  "title": "Calculus I",
  "start": "2018-01-08T09:00:00",
  "timeZone": "Europe/London",
  "duration": "PT1H30M",
  "locations": {
    "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
      "title": "Math lab room 1",
      "description": "Math Lab I, Department of Mathematics"
  "recurrenceRule": {
    "frequency": "weekly",
    "until": "2018-06-25T09:00:00"
  "recurrenceOverrides": {
    "2018-04-02T09:00:00": null,
    "2018-05-07T09:00:00": null,
    "2018-05-28T09:00:00": null,
    "2018-06-25T09:00:00": {
      "title": "Calculus I Exam",
      "start": "2018-06-25T10:00:00",
      "duration": "PT2H",
      "locations": {
        "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
          "title": "Big Auditorium",
          "description": "Big Auditorium, Other Road"

7.10. Recurring event with participants

This example illustrates scheduled events. A team meeting occurs every week since January 8, 2018 at 9am Johannesburg time. The event owner also chairs the event. Participants meet in a virtual meeting room. An attendee has accepted the invitation, but on March 8, 2018 he is unavailable and declined participation for this occurrence.

  "...": "",
  "title": "FooBar team meeting",
  "start": "2018-01-08T09:00:00",
  "timeZone": "Africa/Johannesburg",
  "duration": "PT1H",
  "locations": {
    "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
      "title": "ChatMe meeting room",
      "rel": "virtual",
      "features": [
      "uri": ""
  "recurrenceRule": {
    "frequency": "weekly"
  "replyTo": {
    "imip": ""
  "participants": {
    "": {
      "name": "Tom Tool",
      "email": "",
      "rsvpResponse": "accepted",
      "roles": [
    "": {
      "name": "Zoe Zelda",
      "email": "",
      "rsvpResponse": "accepted",
      "roles": [
    "...": ""
  "recurrenceOverrides": {
    "2018-03-08T09:00:00": {
      "participants/": "declined"

8. Security Considerations

The use of JSON as a format does have its own inherent security risks as discussed in Section 12 of [RFC8259]. Even though JSON is considered a safe subset of JavaScript, it should be kept in mind that a flaw in the parser processing JSON could still impose a threat, which doesn't arise with conventional iCalendar data.

With this in mind, a parser for JSON data aware of the security implications should be used for the format described in this document. For example, the use of JavaScript's eval() function is considered an unacceptable security risk, as described in Section 12 of[RFC8259]. A native parser with full awareness of the JSON format should be preferred.

9. IANA Considerations

This document amends the application/calendar MIME media type defined in [RFC7265].

New optional parameter: type with value being one of jsevent, jstask, jsgroup. The parameter MUST NOT occur more than once.

10. Acknowledgments

The authors would like to thank the members of CalConnect for their valuable contributions. This specification originated from the work of the API technical committee of CalConnect, the Calendaring and Scheduling Consortium.

11. References

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2183] Troost, R., Dorner, S. and K. Moore, "Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", RFC 2183, DOI 10.17487/RFC2183, August 1997.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005.
[RFC4122] Leach, P., Mealling, M. and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI 10.17487/RFC4122, July 2005.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006.
[RFC4791] Daboo, C., Desruisseaux, B. and L. Dusseault, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, DOI 10.17487/RFC4791, March 2007.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, DOI 10.17487/RFC5545, September 2009.
[RFC5546] Daboo, C., "iCalendar Transport-Independent Interoperability Protocol (iTIP)", RFC 5546, DOI 10.17487/RFC5546, December 2009.
[RFC5646] Phillips, A. and M. Davis, "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, September 2009.
[RFC5870] Mayrhofer, A. and C. Spanring, "A Uniform Resource Identifier for Geographic Locations ('geo' URI)", RFC 5870, DOI 10.17487/RFC5870, June 2010.
[RFC6047] Melnikov, A., "iCalendar Message-Based Interoperability Protocol (iMIP)", RFC 6047, DOI 10.17487/RFC6047, December 2010.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M. and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012.
[RFC6838] Freed, N., Klensin, J. and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013.
[RFC6901] Bryan, P., Zyp, K. and M. Nottingham, "JavaScript Object Notation (JSON) Pointer", RFC 6901, DOI 10.17487/RFC6901, April 2013.
[RFC7265] Kewisch, P., Daboo, C. and M. Douglass, "jCal: The JSON Format for iCalendar", RFC 7265, DOI 10.17487/RFC7265, May 2014.
[RFC7493] Bray, T., "The I-JSON Message Format", RFC 7493, DOI 10.17487/RFC7493, March 2015.
[RFC7529] Daboo, C. and G. Yakushev, "Non-Gregorian Recurrence Rules in the Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 7529, DOI 10.17487/RFC7529, May 2015.
[RFC7986] Daboo, C., "New Properties for iCalendar", RFC 7986, DOI 10.17487/RFC7986, October 2016.
[RFC8259] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017.

11.2. Informative References

[draft-apthorp-ical-tasks] "Task Extensions to iCalendar"
[draft-daboo-valarm-extensions] "VALARM Extensions for iCalendar"
[draft-ietf-calext-eventpub-extensions] "Event Publishing Extensions to iCalendar"
[draft-ietf-calext-ical-relations] "Support for iCalendar Relationships"

Authors' Addresses

Neil Jenkins FastMail PO Box 234 Collins St West Melbourne, VIC 8007 Australia EMail: URI:
Robert Stepanek FastMail PO Box 234 Collins St West Melbourne, VIC 8007 Australia EMail: URI: