Calendaring extensions N. Jenkins
Internet-Draft R. Stepanek
Intended status: Standards Track Fastmail
Expires: January 24, 2020 July 23, 2019

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, and over time successor to, the widely deployed iCalendar data format and to be unambiguous, extendable and simple to process. In contrast to the JSON-based jCal format, it is not a direct mapping from iCalendar and expands semantics where appropriate.

Status of This Memo

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This Internet-Draft will expire on January 24, 2020.

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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 is mostly a pragmatic choice: its widespread use makes JSCalendar easier to adopt, and the ready availability of production-ready JSON implementations eliminates a whole category of parser-related interoperability issues, which iCalendar has often suffered from.

1.1. Motivation and Relation to iCalendar and jCal

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 and often leads to implementation errors. 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. The definition of recurrence rules is ambiguous and has resulted in differing understandings even between experienced calendar developers.

In recent years, many new products and services have appeared that wish to use a JSON representation of calendar data within their API. The JSON format for iCalendar data, jCal, is a direct mapping between iCalendar and JSON. In its effort to represent full iCalendar semantics, it inherits all the same pitfalls and uses a complicated JSON structure unlike most common JSON data representations.

As a consequence, since the standardization of jCal, the majority of implementations and service providers either kept using iCalendar, or came up with their own proprietary JSON representations, which are incompatible with each other and often suffer from common pitfalls, such as storing event start times in UTC (which become incorrect if the timezone's rules change in the future). JSCalendar is intended to meet this demand for JSON-formatted calendar data, and to provide a standard, elegant representation as an alternative to new proprietary formats.

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.

1.3. Type Signatures

Type signatures are given for all JSON values in this document. The following conventions are used:

Other types may also be given, with their representation defined elsewhere in this document.

1.4. Data Types

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

1.4.1. Int

Where Int is given as a data type, it means an integer in the range -2^53+1 <= value <= 2^53-1, the safe range for integers stored in a floating-point double, represented as a JSON Number.

1.4.2. UnsignedInt

Where UnsignedInt is given as a data type, it means an Int where the value MUST be in the range 0 <= value <= 2^53-1.

1.4.3. UTCDateTime

This is a string in [RFC3339] date-time format, with the further restrictions that any letters MUST be in uppercase, the time component MUST be included and the time offset MUST be the character Z. 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.

1.4.4. LocalDateTime

This is a date-time string with no time zone/offset information. It is otherwise in the same format as UTCDateTime, including fractional seconds. For example 2006-01-02T15:04:05 and 2006-01-02T15:04:05.003 are both valid. The time zone to associate the LocalDateTime 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 time zone at the same wall-clock time (as opposed to the same instant point in time).

1.4.5. Duration

Where Duration is given as a type, it means a length of time 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"
    dur-week    = 1*DIGIT "W"

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

In addition, the duration MUST NOT include fractional second values unless the fraction is non-zero.

1.4.6. SignedDuration

A SignedDuration represents a length of time that may be positive or negative and is typically used to express the offset of a point in time relative to an associated time. It is represented as a Duration, optionally preceded by a sign character. It is specified by the following ABNF:

    signed-duration = (["+"] / "-") duration

A negative sign indicates a point in time at or before the associated time, a positive or no sign a time at or after the associated time.

1.4.7. Id

Where Id is given as a data type, it means a String of at least 1 and a maximum of 255 octets in size, and it MUST only contain characters from the "URL and Filename Safe" base64 alphabet, as defined in Section 5 of [RFC4648], excluding the pad character (=). This means the allowed characters are the ASCII alphanumeric characters (A-Za-z0-9), hyphen (-), and underscore (_).

Unless otherwise specified, Ids are arbitrary and only have meaning within the object where they are being used. Ids need not be unique between different objects. For example, two JSEvent objects MAY use the same ids in their respective links properties. Or within the same JSEvent object the same Id could appear in the participants and alerts properties. This does not imply any semantic connection between the two.

Nevertheless, a UUID is typically a good choice.

1.4.8. PatchObject

A PatchObject is of type String[*], 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/foo/offset and alerts.

The value associated with each pointer is either:

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

1.4.9. Time Zones

By default, time zones in JSCalendar are identified by their name in the IANA Time Zone Database, and the zone rules of the respective zone record apply.

Implementations MAY embed the definition of custom time zones in the timeZones property (see Section 4.7.2).

2. JSCalendar Objects

This section describes the calendar object types specified by JSCalendar.

2.1. JSEvent

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

A JSGroup is a collection of JSEvent and/or 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. Properties are specified as being either mandatory or optional. Optional properties may have a default value, if explicitly specified in the property definition.

3.1. Normalization and Equivalence

JSCalendar aims to provide unambiguous definitions for value types and properties, but does not define a general normalization 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).

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

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

3.2. 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.

Vendors are strongly encouraged to standardize any new property values or extensions that are useful to other systems as well, rather than use a vendor-specific prefix.

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 5 describe the set of supported properties per type.

4.1. Metadata Properties

4.1.1. @type

Type: String (mandatory).

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:

4.1.2. uid

Type: String (mandatory).

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.

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.

4.1.3. relatedTo

Type: String[Relation] (optional).

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 property:

Note, the Relation object only has one property; it is specified as an object with a single property rather than mapping directly from the UID to relation types to allow for extension in the future.

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 occurrences after the split. A next relation MUST be set on the original object's relatedTo property for the UID of the new object. A first relation for 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 (optional).

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 of [RFC5545]).

This property SHOULD NOT be used to alter the interpretation of a 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: UTCDateTime (optional).

The date and time this object was initially created.

4.1.6. updated

Type: UTCDateTime (mandatory).

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

4.1.7. sequence

Type: UnsignedInt (optional, default: 0).

Initially zero, this MUST be incremented by one every time a change is made to the object, except if the change only modifies the participants property (see Section 4.4.5).

This is used as part of iTIP [RFC5546] to know which version of the object a scheduling message relates to.

4.1.8. method

Type: String (optional).

The iTIP [RFC5546] method, in lowercase. This MUST only be present if the JSCalendar object represents an iTIP scheduling message.

4.2. What and Where Properties

4.2.1. title

Type: String (optional, default: empty String).

A short summary of the object.

4.2.2. description

Type: String (optional, default: empty String).

A longer-form text description of the object. The content is formatted according to the descriptionContentType property.

4.2.3. descriptionContentType

Type: String (optional, default: text/plain).

Describes the media type [RFC6838] of the contents of the description property. Media types MUST be sub-types of type text, and SHOULD be text/plain or text/html [MIME]. They MAY define parameters and the charset parameter value MUST be utf-8, if specified. Descriptions of type text/html MAY contain cid URLs [RFC2392] to reference links in the calendar object by use of the cid property of the Link object.

4.2.4. showWithoutTime

Type: Boolean (optional, default: false).

Indicates the time is not important to display to the user when rendering this calendar object, for example an event that conceptually occurs all day or across multiple days, such as "New Year's Day" or "Italy Vacation". While the time component is important for free-busy calculations and checking for scheduling clashes, calendars may choose to omit displaying it and/or display the object separately to other objects to enhance the user's view of their schedule.

Such events are also commonly known as "all-day" events.

4.2.5. locations

Type: Id[Location] (optional).

A map of location ids to Location objects, representing locations associated with the object.

A Location object has the following properties. It MUST have at least one property other than the relativeTo property.

4.2.6. virtualLocations

Type: Id[VirtualLocation] (optional).

A map of ids to VirtualLocation objects, representing virtual locations, such as video conferences or chat rooms, associated with the object.

A VirtualLocation object has the following properties.

4.2.7. links

Type: Id[Link] (optional).

A map of link ids to Link objects, representing external resources associated with the object.

A Link object has the following properties:

4.2.8. locale

Type: String (optional).

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

4.2.9. keywords

Type: String[Boolean] (optional).

A set of keywords or tags that relate to the object. The set is represented as a map, with the keys being the keywords. The value for each key in the map MUST be true.

4.2.10. categories

Type: String[Boolean] (optional).

A set of categories that relate to the calendar object. The set is represented as a map, with the keys being the categories specified as URIs. The value for each key in the map MUST be true.

In contrast to keywords, categories typically are structured. For example, a vendor owning the domain might define the categories" and

4.2.11. color

Type: String (optional).

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

Some events and tasks occur at regular, or indeed irregular, intervals. Rather than having to copy the data for every occurrence, you can instead have a master event with a recurrence rule generating the occurrences, and/or overrides that add extra dates or exceptions to the rule.

4.3.1. recurrenceId

Type: LocalDateTime (optional).

If present, this JSCalendar object represents one occurrence of a recurring JSCalendar object. If present the recurrenceRule and recurrenceOverrides properties MUST NOT be present.

The value is a date-time either produced by the recurrenceRule of the master event, or added as a key to the recurrenceOverrides property of the master event.

4.3.2. recurrenceRule

Type: Recurrence (optional).

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

A JSEvent recurs by applying the recurrence rule to the start date-time.

A JSTask recurs by applying the recurrence rule to the start date-time, if defined, otherwise it recurs by the due date-time, if defined. If the task defines neither a start nor due date-time, its recurrenceRule property value MUST be null.

A Recurrence object is a JSON object mapping of a RECUR value type in iCalendar [RFC5545] [RFC7529] and has the same semantics. It has the following properties: Interpreting recurrence rules

A recurrence rule specifies a set of date-times for recurring calendar objects. A recurrence rule has the following semantics. Note, wherever "year", "month" or "day of month" is used, this is within the calendar system given by the "rscale" property, which defaults to gregorian if omitted.

  1. A set of candidates is generated. This is every second within a period defined by the frequency property value:
  2. Each date-time candidate is compared against all of the byX properties of the rule except bySetPosition. If any property in the rule does not match the date-time, it is eliminated. Each byX property is an array; the date-time matches the property if it matches any of the values in the array. The properties have the following semantics:

    If a skip property is defined and is not "omit", there may be candidates that do not correspond to valid dates (e.g. 31st February in the gregorian calendar). In this case, the properties MUST be considered in the order above and:

    1. After applying the byMonth filter, if the candidate's month is invalid for the given year increment it (if skip is "forward") or decrement it (if skip is "backward") until a valid month is found, incrementing/decrementing the year as well if you pass through the beginning/end of the year. This only applies to calendar systems with leap months.
    2. After applying the byMonthDay filter, if the day of the month is invalid for the given month and year, change the date to the first day of the next month (if skip == "forward") or the last day of the current month (if skip == "backward").
    3. If any valid date produced after applying the skip is already a candidate, eliminate the duplicate. (For example after adjusting, 30th February and 31st February would both become the same "real" date, so one is eliminated as a duplicate.)

  3. If a bySetPosition property is included, this is now applied to the ordered list of remaining dates. This property specifies the indexes of date-times to keep; all others should be eliminated. Negative numbers are indexes from the end of the list, with -1 being the last item.
  4. Any date-times before the start date of the event are eliminated (see below for why this might be needed).
  5. If a skip property is included and is not "omit", eliminate any date-times that have already been produced by previous iterations of the algorithm. (This is not possible if skip == "omit".)
  6. If further dates are required (we have not reached the until date, or count limit) skip the next (interval - 1) sets of candidates, then continue from step 1.

When determining the set of occurrence dates for an event or task, the following extra rules must be applied:

  1. The initial date-time to which the rule is applied (the start date-time for events; the start or due date-time for tasks) is always the first occurrence in the expansion (and is counted if the recurrence is limited by a "count" property), even if it would normally not match the rule.
  2. The first set of candidates to consider is that which would contain the initial date-time. This means the first set may include candidates before the initial date-time; such candidates are eliminated from the results in step (4) as outlined before.
  3. The following properties MUST be implicitly added to the rule under the given conditions:

4.3.3. recurrenceOverrides

Type: LocalDateTime[PatchObject] (optional).

A map of the recurrence ids (the date-time produced by the recurrence rule) to an object of patches to apply to the generated occurrence object.

If the recurrence id does not match a date-time from the recurrence rule (or no rule is specified), it is to be treated as an additional occurrence (like an RDATE from iCalendar). The patch object may often be empty in this case.

If the patch object defines the excluded property value to be true, then the recurring calendar object does not occur at the recurrence id date-time (like an EXDATE from iCalendar). Such a patch object MUST NOT patch any other property.

By default, an occurrence inherits all properties from the main object except the start (or due) date-time, which is shifted to match the recurrence id LocalDateTime. However, individual properties of the occurrence can be modified by a patch, or multiple patches. It is valid to patch the start property value, and this patch takes precedence over the value generated from the recurrence id. Both the recurrence id as well as the patched start date-time may occur before the original JSCalendar object's start or due date.

A pointer in the PatchObject MUST be ignored if it starts with one of the following prefixes:

4.3.4. excluded

Type: Boolean (optional, default: false).

Defines if this object is an overridden, excluded instance of a recurring JSCalendar object (see Section 4.3.3). If this property value is true, this calendar object instance MUST be removed from the occurrence expansion. The absence of this property or its default value false indicates that this instance MUST be included in the occurrence expansion.

4.4. Sharing and Scheduling Properties

4.4.1. priority

Type: Int (optional, default: 0).

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 (optional, default: busy).

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

4.4.3. privacy

Type: String (optional, default: public).

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 API via which this object is accessed.

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] (optional).

Represents methods by which participants may submit their RSVP response to the organizer of the calendar object. The keys in the property value are the available methods and MUST only contain ASCII alphanumeric characters (A-Za-z0-9). 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, but MUST preserve the method key and URI. This property MUST be omitted if no method is defined (rather than an empty object). If this property is set, the participants property of this calendar object MUST contain at least one participant.

The following methods are defined:

4.4.5. participants

Type: Id[Participant] (optional).

A map of participant ids to participants, describing their participation in the calendar object.

If this property is set, then the replyTo property of this calendar object MUST define at least one reply method.

A Participant object has the following properties:

4.5. Alerts Properties

4.5.1. useDefaultAlerts

Type: Boolean (optional, default: false).

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: Id[Alert] (optional).

A map of alert ids to Alert objects, representing alerts/reminders to display or send to the user for this calendar object.

An Alert Object has the following properties:

4.6. Multilingual Properties

4.6.1. localizations

Type: String[PatchObject] (optional).

A map of [RFC5646] language tags to patch objects, which localize the calendar object into the locale of the respective language tag.

See the description of PatchObject for the structure of the PatchObject. The patches are applied to the top-level calendar object. In addition, the locale property of the patched object is set to the language tag. All pointers for patches MUST end with one of the following suffixes; any patch that does not follow this MUST be ignored unless otherwise specified in a future RFC: recurrenceOverrides/2018-01-05T14:00:00/locations/abcd1234/title is permissible, but a patch to uid is not.

For example, a patch to

Note that this specification does not define how to maintain validity of localized content. For example, a client application changing a JSCalendar object's title property might also need to update any localizations of this property. Client implementations SHOULD provide the means to manage localizations, but how to achieve this is specific to the application's workflow and requirements.

4.7. Time Zone Properties

4.7.1. timeZone

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

Identifies the time zone the object is scheduled in, or null for floating time. This is either a name from the IANA Time Zone Database or the id of a custom time zone from the timeZones property (see Section 1.4.9). If omitted, this MUST be presumed to be null (i.e., floating time).

4.7.2. timeZones

Type: String[TimeZone] (optional).

Maps identifiers of custom time zones to their time zone definition. The following restrictions apply for each key in the map:

An identifier need only be unique to this JSCalendar object.

A TimeZone object maps a VTIMEZONE component from iCalendar [RFC5545] and the semantics are as defined there. A valid time zone MUST define at least one transition rule in the standard or daylight property. Its properties are:

A TimeZoneRule object maps a STANDARD or DAYLIGHT sub-component from iCalendar, with the restriction that at most one recurrence rule is allowed per rule. It 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: LocalDateTime (mandatory).

The date/time the event starts in the event's time zone (as specified in the timeZone property, see Section 4.7.1).

5.1.2. duration

Type: Duration (optional, default: PT0S).

The zero or positive duration of the event in the event's start time zone.

Note that a duration specified using weeks or days does not always correspond to an exact multiple of 24 hours. The number of hours/minutes/seconds may vary if it overlaps a period of discontinuity in the event's time zone, for example a change from standard time to daylight-savings time. Leap seconds MUST NOT be considered when computing an exact duration. When computing an exact duration, the greatest order time components MUST be added first, that is, the number of days MUST be added first, followed by the number of hours, number of minutes, and number of seconds. Fractional seconds MUST be added last. These semantics match the iCalendar DURATION value type ([RFC5545], Section 3.3.6).

A JSEvent MAY involve start and end locations that are in different time zones (e.g. a trans-continental flight). This can be expressed using the relativeTo and timeZone properties of the JSEvent's Location objects (see Section 4.2.5).

5.1.3. status

Type: String (optional, default: confirmed).

The scheduling status (Section 4.4) of a JSEvent. 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: LocalDateTime (optional).

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

5.2.2. start

Type: LocalDateTime (optional).

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

5.2.3. estimatedDuration

Type: Duration (optional).

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

5.2.4. statusUpdatedAt

Type: UTCDateTime (optional).

Specifies the date/time the status property of either the task overall (Section 5.2.6) or a specific participant (Section 5.2.5) was last updated.

If the task is recurring and has future instances, a client may want to keep track of the last status update timestamp of a specific task recurrence, but leave other instances unchanged. One way to achieve this is by overriding the statusUpdatedAt property in the task recurrenceOverrides property. However, this could produce a long list of timestamps for regularly recurring tasks. An alternative approach is to split the JSTask into a current, single instance of JSTask with this instance status update time and a future recurring instance. See also Section 4.1.3 on splitting.

5.2.5. 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:

5.2.6. status

Type: String (optional).

Defines the overall status of this task. If omitted, the default 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 common JSCalendar properties:

In addition, the following JSGroup-specific properties are supported:

5.3.1. entries

Type: String[JSTask|JSEvent] (mandatory).

A collection of group members. This is represented as a map of the uid property value to the JSCalendar object member having that uid. Implementations MUST ignore entries of unknown type.

5.3.2. source

Type: String (optional).

The source from which updated versions of this group may be retrieved from. The value MUST be a URI.

6. 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.

6.1. 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 at 2pm.

  "@type": "jsevent",
  "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f1",
  "updated": "2018-01-01T12:00:00Z",
  "title": "Some event",
  "start": "2018-01-15T13:00:00",
  "timeZone": "America/New_York",
  "duration": "PT1H"

6.2. Simple Task

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

  "@type": "jstask",
  "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
  "updated": "2018-01-19T18:00:00Z",
  "title": "Do something"

6.3. 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",
  "title": "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"

6.4. 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",
  "showWithoutTime": true,
  "start": "1900-04-01T00:00:00",
  "duration": "P1D",
  "recurrenceRule": {
    "frequency": "yearly"

6.5. 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"

6.6. 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. The location names can serve as input for navigation systems.

  "...": "",
  "title": "Flight XY51 to Tokyo",
  "start": "2018-04-01T09:00:00",
  "timeZone": "Europe/Berlin",
  "duration": "PT10H30M",
  "locations": {
    "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
      "rel": "start",
      "name": "Frankfurt Airport (FRA)"
    "c2c7ac67-dc13-411e-a7d4-0780fb61fb08": {
      "rel": "end",
      "name": "Narita International Airport (NRT)",
      "timeZone": "Asia/Tokyo"

6.7. 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"

6.8. Event with Multiple Locations and Localization

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. The event title and descriptions are localized.

  "...": "",
  "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": {
    "c0503d30-8c50-4372-87b5-7657e8e0fedd": {
      "name": "The Music Bowl",
      "description": "Music Bowl, Central Park, New York",
      "coordinates": "geo:40.7829,73.9654"
  "virtualLocations": {
    "6f3696c6-1e07-47d0-9ce1-f50014b0041a": {
      "name": "Free live Stream from Music Bowl",
      "uri": ""
  "localizations": {
    "de": {
      "title": "Live von der Music Bowl: The Band!",
      "description": "Schau dir das größte Musikereignis an!",
                              "Gratis Live-Stream aus der Music Bowl"

6.9. 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 (inclusive). Each lecture lasts for one hour and thirty 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 no course is held. On January 5 at 2pm is an optional introduction course, that occurs before the first regular lecture.

  "...": "",
  "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\n1 University Drive"
  "recurrenceRule": {
    "frequency": "weekly",
    "until": "2018-06-25T09:00:00"
  "recurrenceOverrides": {
    "2018-01-05T14:00:00": {
      "title": "Introduction to Calculus I (optional)"
    "2018-04-02T09:00:00": {
      "excluded": true
    "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"

6.10. 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, leaving a short explanation for the organizer.

  "...": "",
  "title": "FooBar team meeting",
  "start": "2018-01-08T09:00:00",
  "timeZone": "Africa/Johannesburg",
  "duration": "PT1H",
  "virtualLocations": {
    "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
      "name": "ChatMe meeting room",
      "uri": ""
  "recurrenceRule": {
    "frequency": "weekly"
  "replyTo": {
    "imip": ""
  "participants": {
    "dG9tQGZvb2Jhci5leGFtcGxlLmNvbQ": {
      "name": "Tom Tool",
      "email": "",
      "sendTo": {
        "imip": ""
      "participationStatus": "accepted",
      "roles": {
        "attendee": true
    "em9lQGZvb2Jhci5leGFtcGxlLmNvbQ": {
      "name": "Zoe Zelda",
      "email": "",
      "sendTo": {
        "imip": ""
      "participationStatus": "accepted",
      "roles": {
        "owner": true,
        "attendee": true,
        "chair": true
    "...": ""
  "recurrenceOverrides": {
   "2018-03-08T09:00:00": {
                      "Sorry, kid's recital this week, can't make it."

7. Security Considerations

Calendaring and scheduling information is very privacy-sensitive. The transmission of such information must be careful to protect it from possible threats, such as eavesdropping, replay, message insertion, deletion, modification, and man-in-the-middle attacks. This document just defines the data format; such considerations are primarily the concern of the API or method of storage and transmission of such files.

7.1. Expanding Recurrences

A recurrence rule may produce infinite occurrences of an event. Implementations MUST handle expansions carefully to prevent accidental or deliberate resource exhaustion.

Conversely, a recurrence rule may be specified that does not expand to anything. It is not always possible to tell this through static analysis of the rule, so implementations MUST be careful to avoid getting stuck in an infinite loop, or otherwise exhausting resources, searching for the next occurrence.

7.2. JSON Parsing

The Security Considerations of [RFC8259] apply to the use of JSON as the data interchange format.

As for any serialization format, parsers need to thoroughly check the syntax of the supplied data. JSON uses opening and closing tags for several types and structures, and it is possible that the end of the supplied data will be reached when scanning for a matching closing tag; this is an error condition, and implementations need to stop scanning at the end of the supplied data.

JSON also uses a string encoding with some escape sequences to encode special characters within a string. Care is needed when processing these escape sequences to ensure that they are fully formed before the special processing is triggered, with special care taken when the escape sequences appear adjacent to other (non-escaped) special characters or adjacent to the end of data (as in the previous paragraph).

If parsing JSON into a non-textual structured data format, implementations may need to allocate storage to hold JSON string elements. Since JSON does not use explicit string lengths, the risk of denial of service due to resource exhaustion is small, but implementations may still wish to place limits on the size of allocations they are willing to make in any given context, to avoid untrusted data causing excessive memory allocation.

7.3. URI Values

Several JSCalendar properties contain URIs as values, and processing these properties requires extra care. Section 7 of [RFC3986] discusses security risk related to URIs.

8. IANA Considerations

This document defines a MIME media type for use with JSCalendar data formatted in JSON.

Type name:
Subtype name:
Required parameters:

The type parameter conveys the type of the JSCalendar data in the body part, with the value being one of jsevent, jstask, or jsgroup. The parameter MUST NOT occur more than once. It MUST match the value of the @type property of the JSON-formatted JSCalendar object in the body.
Optional parameters:
Encoding considerations:
Same as encoding considerations of application/json as specified in RFC8529, Section 11.
Security considerations:
See Section 7 of this document.
Interoperability considerations:
This media type provides an alternative to iCalendar, jCal and proprietary JSON-based calendaring data formats.
Published specification:
This specification.
Applications that use this media type:
Applications that currently make use of the text/calendar and application/calendar+json media types can use this as an alternative. Similarly, applications that use the application/json media type to transfer calendaring data can use this to further specify the content.
Fragment identifier considerations:
Additional information:
Magic number(s):
File extensions(s):
Macintosh file type code(s):

Person & email address to contact for further information:
Intended usage:
Restrictions on usage:
See the "Author's Address" section of this document.
Change controller:

9. 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.

10. References

10.1. 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.
[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.
[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.
[RFC7808] Douglass, M. and C. Daboo, "Time Zone Data Distribution Service", RFC 7808, DOI 10.17487/RFC7808, March 2016.
[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.

10.2. Informative References

[MIME] "IANA Media Types"

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: