The transformer uses `content` if available, or `name` if not, in order to generate status text. The `url` will be appended. The `summary` property will be used as the CW text. The `icon` will be used as a thumbnail.
Mastodon sanitizes incoming HTML in order to not break assumptions for API client developers. Supported elements will be kept as-is, and unsupported elements will be converted or removed. Supported attributes will be kept, and all other attributes will be stripped. The following elements and attributes are supported:
-`<p>`
-`<span>` (`class`)
-`<br>`
-`<a>` (`href`, `rel`, `class`)
- lists will be converted to `<p>`, and list items will be separated with `<br>`
Since Mastodon v4.2, the following elements and attributes are supported:
-`<p>`
-`<span>` (`class`)
-`<br>`
-`<a>` (`href`, `rel`, `class`)
-`<del>`
-`<pre>`
-`<code>`
-`<em>`
-`<strong>`
-`<b>`
-`<i>`
-`<u>`
-`<ul>`
-`<ol>` (`start`, `reversed`)
-`<li>` (`value`)
-`<blockquote>`
- headings will be converted to `<strong>` and then wrapped in `<p>`
The sanitizer will keep classes if they begin with microformats prefixes or are semantic classes:
- h-*
- p-*
- u-*
- dt-*
- e-*
- mention
- hashtag
- ellipsis
- invisible
Links will be kept if the protocol is supported, and converted to text otherwise. The following link protocols are supported:
: Used to determine whether status media or text should be hidden by default. See the [Sensitive content](#sensitive) extension section for more information about `as:sensitive`
: Either `Mention`, `Hashtag`, or `Emoji` is currently supported. See the [Hashtag](#Hashtag) and [Custom emoji](#Emoji) extension sections for more information
: The plain-text Webfinger address of a profile Mention (`@user` or `@user@domain`), or the plain-text Hashtag (`#tag`), or the custom Emoji shortcode (`:thounking:`)
: Used to include attached images, videos, or audio.
attachment[].url
: Used to fetch the media attachment
attachment[].summary
: Used as media description
attachment[].blurhash
: Used to generate a blurred preview image corresponding to the colors used within the image. See [Blurhash](#blurhash) for more details.
replies
: A Collection of statuses that are in reply to the current status. Up to 5 replies from the same server will be fetched upon discovery of a remote status, in order to resolve threads more fully. On Mastodon's side, the first page contains self-replies, and additional pages contain replies from other people.
#### Poll-specific properties
endTime
: The timestamp for when voting will close on the poll
closed
: The timestamp for when voting closed on the poll. The timestamp will likely match the `endTime` timestamp. If this property is present, the poll is assumed to be closed.
votersCount
: How many people have voted in the poll. Distinct from how many votes have been cast (in the case of multiple-choice polls)
: Indicate interest in receiving status updates from a profile.
Accept/Reject
: Used to approve or deny Follow activities. Unlocked accounts will automatically reply with an Accept, while locked accounts can manually choose whether to approve or deny a follow request.
Add/Remove
: Manage pinned posts and featured collections.
Update
: Refresh account details
Delete
: Remove an account from the database, as well as all of their statuses.
Undo
: Undo a previous Follow, Accept Follow, or Block.
## Extensions defined using ActivityStreams vocabulary
While the Activity Vocabulary defines a wide range of types and terms, ActivityPub only defines side effects for a subset of them. The following activity types have the following side effects when received in a Mastodon inbox.
### Remote blocking (`Block`) {#Block}
ActivityPub defines the `Block` activity for client-to-server (C2S) use-cases, but not for server-to-server (S2S) -- it recommends that servers SHOULD NOT deliver Block activities to their `object`. However, Mastodon will send this activity when a local user blocks a remote user. When Mastodon receives a `Block` activity where the `object` is an actor on the local domain, it will interpret this as a signal to hide the actor's profile and posts from the local user, as well as disallowing mentions of that actor by that local user.
To report profiles and/or posts on remote servers, Mastodon will send a `Flag` activity from the instance actor. The `object` of this activity contains the user being reported, as well as any posts attached to the report. If a comment is attached to the report, it will be used as the `content` of the activity.
Mastodon uses the Move activity to signal that an account has migrated to a different account. For the migration to be considered valid, Mastodon checks that the new account has defined an alias pointing to the old account (via the `alsoKnownAs` property).
The ActivityStreams Vocabulary specification describes loosely (non-normatively) how a question might be represented. Mastodon's implementation of polls is somewhat inspired by this section. The following implementation details can be observed:
-`Question` is used as an `Object` type instead of as an `IntransitiveActivity`; rather than being sent directly, it is wrapped in a `Create` just like any other status.
- Poll options are serialized using `oneOf` or `anyOf` as an array.
- Each item in this array has no `id`, has a `type` of `Note`, and has a `name` representing the text of the poll option.
- Each item in this array also has a `replies` property, representing the responses to this particular poll option. This node has no `id`, has a `type` of `Collection`, and has a `totalItems` property representing the total number of votes received for this option.
"content": "What should I eat for breakfast today?",
"published": "2023-03-05T07:40:13Z",
"endTime": "2023-03-06T07:40:13Z",
"votersCount": 7,
"anyOf": [
{
"type": "Note",
"name": "apple",
"replies": {
"type": "Collection",
"totalItems": 3
}
},
{
"type": "Note",
"name": "orange",
"replies": {
"type": "Collection",
"totalItems": 7
}
},
{
"type": "Note",
"name": "banana",
"replies": {
"type": "Collection",
"totalItems": 6
}
}
]
}
```
- Poll votes are serialized as `Create` activities, where the `object` is a `Note` with a `name` that exactly matches the `name` of the poll option. The `Note.inReplyTo` points to the URI of the `Question` object.
- For multiple-choice polls, multiple activities may be sent. Votes will be counted if you have not previously voted for that option.
### Mentions for addressing and notifications {#Mention}
{{<caption-linkurl="https://www.w3.org/TR/activitystreams-vocabulary/#microsyntaxes"caption="Activity Vocabulary §5.6 - Mentions, Tags, and Other Common Social Microsyntaxes">}}
In the ActivityStreams Vocabulary, `Mention` is a subtype of `Link` that is intended to represent the microsyntax of @mentions. The `tag` property is intended to add references to other Objects or Links. For Link tags, the `name` of the Link should be a substring of the natural language properties (`name`, `summary`, `content`) on that object. Wherever such a substring is found, it can be transformed into a hyperlink reference to the `href`.
However, Mastodon also uses `Mention` tags for addressing in some cases. Based on the presence or exclusion of Mention tags, and compared to the explicitly declared audiences in `to` and `cc`, Mastodon will calculate a visibility level for the post. Additionally, Mastodon requires Mention tags in order to generate a notification. (The mentioned actor must still be included within `to` or `cc` explicitly in order to receive the post.)
-`public`: Public statuses have the `as:Public` magic collection in `to`
-`unlisted`: Unlisted statuses have the `as:Public` magic collection in `cc`
-`private`: Followers-only statuses have an actor's follower collection in `to` or `cc`, but do not include the `as:Public` magic collection
-`limited`: Limited-audience statuses have actors in `to` or `cc`, at least one of which is not `Mention`ed in `tag`
-`direct`: Mentions-only statuses have actors in `to` or `cc`, all of which are `Mention`ed in `tag`
Public keys are used for HTTP Signatures and Linked Data Signatures. This is implemented using an extra property `publicKey` on actor objects. See [Security]({{< relref "spec/security" >}}) for more information.
"publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvXc4vkECU2/CeuSo1wtn\nFoim94Ne1jBMYxTZ9wm2YTdJq1oiZKif06I2fOqDzY/4q/S9uccrE9Bkajv1dnkO\nVm31QjWlhVpSKynVxEWjVBO5Ienue8gND0xvHIuXf87o61poqjEoepvsQFElA5ym\novljWGSA/jpj7ozygUZhCXtaS2W5AD5tnBQUpcO0lhItYPYTjnmzcc4y2NbJV8hz\n2s2G8qKv8fyimE23gY1XrPJg+cRF+g4PqFXujjlJ7MihD9oqtLGxbu7o1cifTn3x\nBfIdPythWu5b4cujNsB3m3awJjVmx+MHQ9SugkSIYXV0Ina77cTNS0M2PYiH1PFR\nTwIDAQAB\n-----END PUBLIC KEY-----\n"
What is known in Mastodon as “pinned statuses”, or statuses that are always featured at the top of people’s profiles, is implemented using an extra property `featured` on the actor object that points to a `Collection` of objects.
Mastodon allows users to feature specific hashtags on their profile for easy browsing, as a discoverability mechanism. This is implemented using an extra property `featuredTags` on the actor object that points to a `Collection` of `Hashtag` objects specifically.
Mastodon supports arbitrary profile fields containing name-value pairs. This is implemented using the `attachment` property on actor objects, with objects in the array having a type of `PropertyValue` and a `value` property, both from the schema.org namespace.
As noted above while listing the [schema.org @context extensions](#schema), Mastodon currently incorrectly expects and maps the term `schema` to the base URI `http://schema.org#` instead of to the base URI `https://schema.org/`. Therefore, JSON-LD processors who use the correct context definition will fail to process profile fields correctly.
This property is currently unused/deprecated due to the removal of Keybase support in Mastodon 3.5: <https://github.com/mastodon/mastodon/pull/17045>
{{</hint>}}
Mastodon supports integration with identity providers to prove that a profile is linked to a certain identity. This is implemented using the `attachment` property on actor objects, with objects in the array having a type of `IdentityProof` from the Mastodon namespace. The object also includes `signatureAlgorithm` and `signatureValue` from the W3ID Security Vocabulary namespace.
Mastodon allows users to opt-in or opt-out of discoverability features like the profile directory. This flag may also be used as an indicator of the user's preferences toward being included in external discovery services, such as search engines or other indexing tools. If you are implementing such a tool, it is recommended that you respect this property if it is present. This is implemented using an extra property `discoverable` on objects.
Mastodon reports whether a user was locally suspended, for better handling of these accounts. Suspended accounts in Mastodon return empty data. If a remote account is marked as suspended, it cannot be unsuspended locally. Suspended accounts can be targeted by activities such as Update, Undo, Reject, and Delete. This functionality is implemented using an extra property `suspended` on objects.
Similar to the `Mention` subtype of Link already defined in ActivityStreams, Mastodon will use `Hashtag` as a subtype of Link in order to surface posts referencing some common topic identified by a string key. The Hashtag has a `name` containing the #hashtag microsyntax -- a `#` followed by a string sequence representing a topic. This is similar to the @mention microsyntax, where an `@` is followed by some string sequence representing a resource (where in Mastodon's case, this resource is expected to be an account). Mastodon will also normalize hashtags to be case-insensitive lowercase strings, performing ASCII folding and removing invalid characters.
Mastodon supports arbitrary emojis by including a `tag` of the `Emoji` type. Handling of custom emojis is similar to handling of mentions and hashtags, where the `name` of the tagged entity is found as a substring of the natural language properties (`name`, `summary`, `content`) and then linked to the local representation of some resource or topic. In the case of emoji shortcodes, the `name` is replaced by the HTML for an inline image represented by the `icon` property (where `icon.url` links to the image resource).
Mastodon supports setting a focal point on uploaded images, so that wherever that image is displayed, the focal point stays in view. This is implemented using an extra property `focalPoint` on `Image` objects. The property is an array of two floating points between -1.0 and 1.0, with 0,0 being the center of the image, the first value being x (-1.0 is the left edge, +1.0 is the right edge) and the second value being y (-1.0 is the bottom edge, +1.0 is the top edge). See [API Guidelines > Focal points]({{< relref "api/guidelines#focal-points" >}}) for more information.
{{<figuresrc="/assets/focal-points.jpg"caption="A demonstration of various focal points and their coordinates.">}}
The focal point of (-0.55, 0.43) in the example above corresponds to a point 55% to the left of center and 43% above center. This focal point should remain visible within the cropped thumbnail, if any cropping is done.
Mastodon generates colorful preview thumbnails for attachments. This is implemented using an extra property `blurhash` on `Image` objects. The property is a string generated by the [BlurHash algorithm](https://blurha.sh).
Mastodon uses the `as:sensitive` extension property to mark certain posts as sensitive. When a post is marked as sensitive, any media attached to it will be hidden by default, and if a `summary` is present, the status `content` will be collapsed behind this summary. In Mastodon, this is known as a **content warning**.
When a Mastodon server runs in secure mode, all cross-server HTTP requests to it must be signed (in other words, even `GET` requests to public resources). That way, the Mastodon server can choose to reject requests from servers it has blocked and avoid "leaking" public information. Mastodon itself uses a dedicated system actor to sign such HTTP requests. See [Security]({{< relref "spec/security" >}}) for more details on HTTP signatures.
Secure mode is the foundation upon which "limited federation mode" is built. A Mastodon server in limited federation mode will only federate with servers its admin has explicitly allowed, and reject all other requests.
Mastodon has a concept of "followers-only" posts, but expanding the followers collection is currently handled at the destination rather than at the origin (i.e., not with explicit addressing). Therefore, a mechanism to detect synchronization issues and correct them is needed. This mechanism must work on partial followers collections, rather than the full collection (which may not be public information).
When delivering a message to a remote user, an optional `Collection-Synchronization` HTTP header is attached, following the same syntax as the `Signature` header, with the following attributes:
-`collectionId` = MUST be the sender's `followers` collection
-`url` = a URL to a partial collection containing the identifiers of the sender's followers residing on the receiver's instance. MUST reside on the same domain as the actor itself, and SHOULD be only accessible with a signed query from the receiver's instance
-`digest` = hexadecimal representation of the XORed SHA256 digests of each of the identifiers in the partial collection