diff --git a/.prettierrc.json b/.prettierrc.json
new file mode 100644
index 0000000..8e34d43
--- /dev/null
+++ b/.prettierrc.json
@@ -0,0 +1,11 @@
+{
+	"trailingComma": "all",
+	"tabWidth": 4,
+	"semi": true,
+	"arrowParens": "always",
+	"bracketSameLine": false,
+	"bracketSpacing": true,
+	"quoteProps": "as-needed",
+	"useTabs": true,
+	"singleQuote": false
+}
\ No newline at end of file
diff --git a/package.json b/package.json
index 9effa26..586bf1a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "activitypub-types",
-	"version": "1.0.4",
+	"version": "1.1.0",
 	"description": "ActivityPub Typescript types",
 	"main": "./dist/index.js",
 	"scripts": {
diff --git a/src/fields/index.ts b/src/fields/index.ts
index 263aaa1..fe3f671 100644
--- a/src/fields/index.ts
+++ b/src/fields/index.ts
@@ -1,27 +1,41 @@
 import {
-    APCollection,
-    APOrderedCollection,
-    APObject,
-    APArticle,
-    APAudio,
-    APDocument,
-    APEvent,
-    APImage,
-    APNote,
-    APPage,
-    APPlace,
-    APProfile,
-    APRelationship,
-    APTombstone,
-    APVideo,
-    APLink,
-    APCollectionPage,
-    APOrderedCollectionPage,
-    APMention,
-} from '../model-interfaces';
+	APArticle,
+	APAudio,
+	APCollection,
+	APCollectionPage,
+	APDocument,
+	APEvent,
+	APImage,
+	APLink,
+	APMention,
+	APNote,
+	APObject,
+	APOrderedCollection,
+	APOrderedCollectionPage,
+	APPage,
+	APPlace,
+	APProfile,
+	APRelationship,
+	APTombstone,
+	APVideo,
+} from "../model-interfaces";
 
 export type AnyCollection = APCollection | APOrderedCollection;
-export type AnyAPObject = APObject | APArticle | APAudio | APDocument | APEvent | APImage | APNote | APPage | APPlace | APProfile | APRelationship | APTombstone | APVideo | AnyCollection;
+export type AnyAPObject =
+	| APObject
+	| APArticle
+	| APAudio
+	| APDocument
+	| APEvent
+	| APImage
+	| APNote
+	| APPage
+	| APPlace
+	| APProfile
+	| APRelationship
+	| APTombstone
+	| APVideo
+	| AnyCollection;
 
 export type DateTime = string | Date;
 export type LanguageTag = string;
@@ -74,7 +88,14 @@ export type AltitudeField = number;
 export type LatitudeField = number;
 export type LongitudeField = number;
 export type RadiusField = number;
-export type UnitsField = 'cm' | 'feet' | 'inches' | 'km' | 'm' | 'miles' | string;
+export type UnitsField =
+	| "cm"
+	| "feet"
+	| "inches"
+	| "km"
+	| "m"
+	| "miles"
+	| string;
 export type ClosedField = string | AnyAPObject | APLink | DateTime | boolean;
 export type FormerTypeField = string;
 export type DeletedField = DateTime;
@@ -92,22 +113,51 @@ export type CollectionItemsField = string | APCollectionPage | APLink;
 export type CollectionPagePartOfField = string | APCollection | APLink;
 export type CollectionPageNextField = string | APCollection | APLink;
 export type CollectionPagePrevField = string | APCollection | APLink;
-export type OrderedCollectionCurrentField = string | APOrderedCollectionPage | APLink;
-export type OrderedCollectionFirstField = string | APOrderedCollectionPage | APLink;
-export type OrderedCollectionLastField = string | APOrderedCollectionPage | APLink;
-export type OrderedCollectionItemsField = string | APOrderedCollectionPage | APLink;
-export type OrderedCollectionPagePartOfField = string | APOrderedCollection | APLink;
-export type OrderedCollectionPageNextField = string | APOrderedCollection | APLink;
-export type OrderedCollectionPagePrevField = string | APOrderedCollection | APLink;
+export type OrderedCollectionCurrentField =
+	| string
+	| APOrderedCollectionPage
+	| APLink;
+export type OrderedCollectionFirstField =
+	| string
+	| APOrderedCollectionPage
+	| APLink;
+export type OrderedCollectionLastField =
+	| string
+	| APOrderedCollectionPage
+	| APLink;
+export type OrderedCollectionItemsField =
+	| string
+	| APOrderedCollectionPage
+	| APLink;
+export type OrderedCollectionPagePartOfField =
+	| string
+	| APOrderedCollection
+	| APLink;
+export type OrderedCollectionPageNextField =
+	| string
+	| APOrderedCollection
+	| APLink;
+export type OrderedCollectionPagePrevField =
+	| string
+	| APOrderedCollection
+	| APLink;
 export type StartIndexField = number;
 export type SourceField = {
-    content: ContentField,
-    mediaType?: MediaType,
-}
+	content: ContentField;
+	mediaType?: MediaType;
+};
 export type InboxField = string | APOrderedCollection | APLink;
 export type OutboxField = string | APOrderedCollection | APLink;
-export type FollowingField = string | APCollection | APOrderedCollection | APLink;
-export type FollowersField = string | APCollection | APOrderedCollection | APLink;
+export type FollowingField =
+	| string
+	| APCollection
+	| APOrderedCollection
+	| APLink;
+export type FollowersField =
+	| string
+	| APCollection
+	| APOrderedCollection
+	| APLink;
 export type LikedField = string | APCollection | APOrderedCollection | APLink;
 export type LikesField = string | APCollection | APOrderedCollection | APLink;
 export type SharesField = string | APCollection | APOrderedCollection | APLink;
@@ -121,10 +171,10 @@ export type ProvideClientKeyField = string;
 export type SignClientKeyField = string;
 export type SharedInboxField = string;
 export type EndpointsField = {
-    proxyUrl?: ProxyUrlField;
-    oauthAuthorizationEndpoint?: OauthAuthorizationEndpointField;
-    oauthTokenEndpoint?: OauthTokenEndpointField;
-    provideClientKey?: ProvideClientKeyField;
-    signClientKey?: SignClientKeyField;
-    sharedInbox?: SharedInboxField;
-}
\ No newline at end of file
+	proxyUrl?: ProxyUrlField;
+	oauthAuthorizationEndpoint?: OauthAuthorizationEndpointField;
+	oauthTokenEndpoint?: OauthTokenEndpointField;
+	provideClientKey?: ProvideClientKeyField;
+	signClientKey?: SignClientKeyField;
+	sharedInbox?: SharedInboxField;
+};
diff --git a/src/index.ts b/src/index.ts
index 8cbac70..dfb8828 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,2 +1,2 @@
-export * from './fields';
-export * from './model-interfaces';
\ No newline at end of file
+export * from "./fields";
+export * from "./model-interfaces";
diff --git a/src/model-interfaces/activities/accept.interface.ts b/src/model-interfaces/activities/accept.interface.ts
index 0dbbb7e..ad4b628 100644
--- a/src/model-interfaces/activities/accept.interface.ts
+++ b/src/model-interfaces/activities/accept.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APAccept = APActivity
+export type APAccept = APActivity & { type: "Accept" };
+
+export const ActivityIsAccept = (
+	activity: APActivity,
+): activity is APAccept => {
+	return activity.type == "Accept";
+};
diff --git a/src/model-interfaces/activities/activity.interface.ts b/src/model-interfaces/activities/activity.interface.ts
index 225fbb0..836a7cb 100644
--- a/src/model-interfaces/activities/activity.interface.ts
+++ b/src/model-interfaces/activities/activity.interface.ts
@@ -1,65 +1,64 @@
-import { APObject } from '../common/object.interface';
+import { APObject } from "../common/object.interface";
 import {
-    ActorField,
-    InstrumentField,
-    ObjectField,
-    OriginField,
-    ResultField,
-    TargetField
-} from '../../fields';
+	ActorField,
+	InstrumentField,
+	ObjectField,
+	OriginField,
+	ResultField,
+	TargetField,
+} from "../../fields";
 
 export interface APActivity extends APObject {
+	/**
+	 * Describes one or more entities that either performed or are expected to perform the activity.
+	 * Any single activity can have multiple actors. The actor MAY be specified using an indirect Link.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#actor Docs}
+	 */
+	actor?: ActorField | ActorField[];
 
-    /**
-     * Describes one or more entities that either performed or are expected to perform the activity.
-     * Any single activity can have multiple actors. The actor MAY be specified using an indirect Link.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#actor Docs}
-     */
-    actor?: ActorField | ActorField[];
+	/**
+	 * When used within an Activity, describes the direct object of the activity.
+	 * For instance, in the activity "John added a movie to his wishlist",
+	 * the object of the activity is the movie added.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#object Docs}
+	 */
+	object?: ObjectField | ObjectField[];
 
-    /**
-     * When used within an Activity, describes the direct object of the activity.
-     * For instance, in the activity "John added a movie to his wishlist",
-     * the object of the activity is the movie added.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#object Docs}
-     */
-    object?: ObjectField | ObjectField[];
+	/**
+	 * Describes the indirect object, or target, of the activity. The precise meaning of the target is largely dependent
+	 * on the type of action being described but will often be the object of the English preposition "to".
+	 * For instance, in the activity "John added a movie to his wishlist", the target of the activity
+	 * is John's wishlist. An activity can have more than one target.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#target Docs}
+	 */
+	target?: TargetField | TargetField[];
 
-    /**
-     * Describes the indirect object, or target, of the activity. The precise meaning of the target is largely dependent
-     * on the type of action being described but will often be the object of the English preposition "to".
-     * For instance, in the activity "John added a movie to his wishlist", the target of the activity
-     * is John's wishlist. An activity can have more than one target.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#target Docs}
-     */
-    target?: TargetField | TargetField[];
+	/**
+	 * Describes the result of the activity. For instance, if a particular action results
+	 * in the creation of a new resource, the result property can be used to describe that new resource.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#result Docs}
+	 */
+	result?: ResultField | ResultField[];
 
-    /**
-     * Describes the result of the activity. For instance, if a particular action results
-     * in the creation of a new resource, the result property can be used to describe that new resource.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#result Docs}
-     */
-    result?: ResultField | ResultField[];
+	/**
+	 * Describes an indirect object of the activity from which the activity is directed.
+	 * The precise meaning of the origin is the object of the English preposition "from".
+	 * For instance, in the activity "John moved an item to List B from List A",
+	 * the origin of the activity is "List A".
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#origin Docs}
+	 */
+	origin?: OriginField | OriginField[];
 
-    /**
-     * Describes an indirect object of the activity from which the activity is directed.
-     * The precise meaning of the origin is the object of the English preposition "from".
-     * For instance, in the activity "John moved an item to List B from List A",
-     * the origin of the activity is "List A".
-     *
-     * {@link https://www.w3.org/ns/activitystreams#origin Docs}
-     */
-    origin?: OriginField | OriginField[];
-
-    /**
-     * Identifies one or more objects used (or to be used)
-     * in the completion of an Activity.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#instrument Docs}
-     */
-    instrument?: InstrumentField | InstrumentField[];
+	/**
+	 * Identifies one or more objects used (or to be used)
+	 * in the completion of an Activity.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#instrument Docs}
+	 */
+	instrument?: InstrumentField | InstrumentField[];
 }
diff --git a/src/model-interfaces/activities/add.interface.ts b/src/model-interfaces/activities/add.interface.ts
index d7083dd..cf0c2ad 100644
--- a/src/model-interfaces/activities/add.interface.ts
+++ b/src/model-interfaces/activities/add.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APAdd = APActivity
+export type APAdd = APActivity & { type: "Add" };
+
+export const ActivityIsAdd = (activity: APActivity): activity is APAdd => {
+	return activity.type == "Add";
+};
diff --git a/src/model-interfaces/activities/announce.interface.ts b/src/model-interfaces/activities/announce.interface.ts
index 3804571..8d0bb77 100644
--- a/src/model-interfaces/activities/announce.interface.ts
+++ b/src/model-interfaces/activities/announce.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APAnnounce = APActivity
+export type APAnnounce = APActivity & { type: "Announce" };
+
+export const ActivityIsAnnounce = (
+	activity: APActivity,
+): activity is APAnnounce => {
+	return activity.type == "Announce";
+};
diff --git a/src/model-interfaces/activities/arrive.interface.ts b/src/model-interfaces/activities/arrive.interface.ts
index f42cc41..31352d3 100644
--- a/src/model-interfaces/activities/arrive.interface.ts
+++ b/src/model-interfaces/activities/arrive.interface.ts
@@ -1,3 +1,9 @@
-import { APIntransitiveActivity } from './intransitive-activity.interface';
+import { APIntransitiveActivity } from "./intransitive-activity.interface";
 
-export type APArrive = APIntransitiveActivity
+export type APArrive = APIntransitiveActivity & { type: "Arrive" };
+
+export const ActivityIsArrive = (
+	activity: APIntransitiveActivity,
+): activity is APArrive => {
+	return activity.type == "Arrive";
+};
diff --git a/src/model-interfaces/activities/block.interface.ts b/src/model-interfaces/activities/block.interface.ts
index cc21153..02c3010 100644
--- a/src/model-interfaces/activities/block.interface.ts
+++ b/src/model-interfaces/activities/block.interface.ts
@@ -1,3 +1,8 @@
-import { APIgnore } from './ignore.interface';
+import { APActivity } from "./activity.interface";
+import { APIgnore } from "./ignore.interface";
 
-export type APBlock = APIgnore
+export type APBlock = APIgnore & { type: "Block" };
+
+export const ActivityIsBlock = (activity: APActivity): activity is APBlock => {
+	return activity.type == "Block";
+};
diff --git a/src/model-interfaces/activities/create.interface.ts b/src/model-interfaces/activities/create.interface.ts
index 0c722be..e1939b0 100644
--- a/src/model-interfaces/activities/create.interface.ts
+++ b/src/model-interfaces/activities/create.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APCreate = APActivity
+export type APCreate = APActivity & { type: "Create" };
+
+export const ActivityIsCreate = (
+	activity: APActivity,
+): activity is APCreate => {
+	return activity.type == "Create";
+};
diff --git a/src/model-interfaces/activities/delete.interface.ts b/src/model-interfaces/activities/delete.interface.ts
index 43bb148..56a71a2 100644
--- a/src/model-interfaces/activities/delete.interface.ts
+++ b/src/model-interfaces/activities/delete.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APDelete = APActivity
+export type APDelete = APActivity & { type: "Delete" };
+
+export const ActivityIsDelete = (
+	activity: APActivity,
+): activity is APDelete => {
+	return activity.type == "Delete";
+};
diff --git a/src/model-interfaces/activities/dislike.interface.ts b/src/model-interfaces/activities/dislike.interface.ts
index de282b2..e7ce179 100644
--- a/src/model-interfaces/activities/dislike.interface.ts
+++ b/src/model-interfaces/activities/dislike.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APDislike = APActivity
+export type APDislike = APActivity & { type: "Dislike" };
+
+export const ActivityIsDislike = (
+	activity: APActivity,
+): activity is APDislike => {
+	return activity.type == "Dislike";
+};
diff --git a/src/model-interfaces/activities/flag.interface.ts b/src/model-interfaces/activities/flag.interface.ts
index b89ce00..feee08b 100644
--- a/src/model-interfaces/activities/flag.interface.ts
+++ b/src/model-interfaces/activities/flag.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APFlag = APActivity
+export type APFlag = APActivity & { type: "Flag" };
+
+export const ActivityIsFlag = (activity: APActivity): activity is APFlag => {
+	return activity.type == "Flag";
+};
diff --git a/src/model-interfaces/activities/follow.interface.ts b/src/model-interfaces/activities/follow.interface.ts
index 3a026d5..2b439d5 100644
--- a/src/model-interfaces/activities/follow.interface.ts
+++ b/src/model-interfaces/activities/follow.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APFollow = APActivity
+export type APFollow = APActivity & { type: "Follow" };
+
+export const ActivityIsFollow = (
+	activity: APActivity,
+): activity is APFollow => {
+	return activity.type == "Follow";
+};
diff --git a/src/model-interfaces/activities/ignore.interface.ts b/src/model-interfaces/activities/ignore.interface.ts
index e1b505e..abefcdd 100644
--- a/src/model-interfaces/activities/ignore.interface.ts
+++ b/src/model-interfaces/activities/ignore.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APIgnore = APActivity
+export type APIgnore = APActivity & { type: "Ignore" };
+
+export const ActivityIsIgnore = (
+	activity: APActivity,
+): activity is APIgnore => {
+	return activity.type == "Ignore";
+};
diff --git a/src/model-interfaces/activities/intransitive-activity.interface.ts b/src/model-interfaces/activities/intransitive-activity.interface.ts
index a87e32d..8df3a73 100644
--- a/src/model-interfaces/activities/intransitive-activity.interface.ts
+++ b/src/model-interfaces/activities/intransitive-activity.interface.ts
@@ -1,3 +1,3 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APIntransitiveActivity = Omit<APActivity, 'object'>
\ No newline at end of file
+export type APIntransitiveActivity = Omit<APActivity, "object">;
diff --git a/src/model-interfaces/activities/invite.interface.ts b/src/model-interfaces/activities/invite.interface.ts
index ec1abd3..8adc52d 100644
--- a/src/model-interfaces/activities/invite.interface.ts
+++ b/src/model-interfaces/activities/invite.interface.ts
@@ -1,3 +1,9 @@
-import { APOffer } from './offer.interface';
+import { APActivity } from "./activity.interface";
 
-export type APInvite = APOffer
+export type APInvite = APActivity & { type: "Invite" };
+
+export const ActivityIsInvite = (
+	activity: APActivity,
+): activity is APInvite => {
+	return activity.type == "Invite";
+};
diff --git a/src/model-interfaces/activities/join.interface.ts b/src/model-interfaces/activities/join.interface.ts
index 3d840c2..f95cea5 100644
--- a/src/model-interfaces/activities/join.interface.ts
+++ b/src/model-interfaces/activities/join.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APJoin = APActivity
+export type APJoin = APActivity & { type: "Join" };
+
+export const ActivityIsJoin = (activity: APActivity): activity is APJoin => {
+	return activity.type == "Join";
+};
diff --git a/src/model-interfaces/activities/leave.interface.ts b/src/model-interfaces/activities/leave.interface.ts
index c07a73c..38f9b0c 100644
--- a/src/model-interfaces/activities/leave.interface.ts
+++ b/src/model-interfaces/activities/leave.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APLeave = APActivity
+export type APLeave = APActivity & { type: "Leave" };
+
+export const ActivityIsLeave = (activity: APActivity): activity is APLeave => {
+	return activity.type == "Leave";
+};
diff --git a/src/model-interfaces/activities/like.interface.ts b/src/model-interfaces/activities/like.interface.ts
index 8b24f69..6c8c46a 100644
--- a/src/model-interfaces/activities/like.interface.ts
+++ b/src/model-interfaces/activities/like.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APLike = APActivity
+export type APLike = APActivity & { type: "Like" };
+
+export const ActivityIsLike = (activity: APActivity): activity is APLike => {
+	return activity.type == "Like";
+};
diff --git a/src/model-interfaces/activities/listen.interface.ts b/src/model-interfaces/activities/listen.interface.ts
index 2ba0af5..5de2ae9 100644
--- a/src/model-interfaces/activities/listen.interface.ts
+++ b/src/model-interfaces/activities/listen.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APListen = APActivity
+export type APListen = APActivity & { type: "Listen" };
+
+export const ActivityIsListen = (
+	activity: APActivity,
+): activity is APListen => {
+	return activity.type == "Listen";
+};
diff --git a/src/model-interfaces/activities/move.interface.ts b/src/model-interfaces/activities/move.interface.ts
index 0d3e3e6..52b94e6 100644
--- a/src/model-interfaces/activities/move.interface.ts
+++ b/src/model-interfaces/activities/move.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APMove = APActivity
+export type APMove = APActivity & { type: "Move" };
+
+export const ActivityIsMove = (activity: APActivity): activity is APMove => {
+	return activity.type == "Move";
+};
diff --git a/src/model-interfaces/activities/offer.interface.ts b/src/model-interfaces/activities/offer.interface.ts
index e211e30..9e9a7fb 100644
--- a/src/model-interfaces/activities/offer.interface.ts
+++ b/src/model-interfaces/activities/offer.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APOffer = APActivity
+export type APOffer = APActivity & { type: "Offer" };
+
+export const ActivityIsOffer = (activity: APActivity): activity is APOffer => {
+	return activity.type == "Offer";
+};
diff --git a/src/model-interfaces/activities/question.interface.ts b/src/model-interfaces/activities/question.interface.ts
index 1613763..4abff03 100644
--- a/src/model-interfaces/activities/question.interface.ts
+++ b/src/model-interfaces/activities/question.interface.ts
@@ -1,30 +1,37 @@
-import {AnyOfField, ClosedField, OneOfField} from '../../fields';
-import { APIntransitiveActivity } from './intransitive-activity.interface';
+import { AnyOfField, ClosedField, OneOfField } from "../../fields";
+import { APIntransitiveActivity } from "./intransitive-activity.interface";
 
 export interface APQuestion extends APIntransitiveActivity {
+	type: "Question";
 
-    /**
-     * Identifies an exclusive option for a Question.
-     * Use of oneOf implies that the Question can have only a single answer.
-     * To indicate that a Question can have multiple answers, use anyOf.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#oneOf Docs}
-     */
-    oneOf?: OneOfField[];
+	/**
+	 * Identifies an exclusive option for a Question.
+	 * Use of oneOf implies that the Question can have only a single answer.
+	 * To indicate that a Question can have multiple answers, use anyOf.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#oneOf Docs}
+	 */
+	oneOf?: OneOfField[];
 
-    /**
-     * Identifies an inclusive option for a Question.
-     * Use of anyOf implies that the Question can have multiple answers.
-     * To indicate that a Question can have only one answer, use oneOf.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#anyOf Docs}
-     */
-    anyOf?: AnyOfField[];
+	/**
+	 * Identifies an inclusive option for a Question.
+	 * Use of anyOf implies that the Question can have multiple answers.
+	 * To indicate that a Question can have only one answer, use oneOf.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#anyOf Docs}
+	 */
+	anyOf?: AnyOfField[];
 
-    /**
-     * Indicates that a question has been closed, and answers are no longer accepted.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#closed Docs}
-     */
-    closed?: ClosedField;
+	/**
+	 * Indicates that a question has been closed, and answers are no longer accepted.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#closed Docs}
+	 */
+	closed?: ClosedField;
 }
+
+export const ActivityIsQuestion = (
+	activity: APIntransitiveActivity,
+): activity is APQuestion => {
+	return activity.type == "Question";
+};
diff --git a/src/model-interfaces/activities/read.interface.ts b/src/model-interfaces/activities/read.interface.ts
index d43d1c9..8709117 100644
--- a/src/model-interfaces/activities/read.interface.ts
+++ b/src/model-interfaces/activities/read.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APRead = APActivity
+export type APRead = APActivity & { type: "Read" };
+
+export const ActivityIsRead = (activity: APActivity): activity is APRead => {
+	return activity.type == "Read";
+};
diff --git a/src/model-interfaces/activities/reject.interface.ts b/src/model-interfaces/activities/reject.interface.ts
index 1392e70..441f340 100644
--- a/src/model-interfaces/activities/reject.interface.ts
+++ b/src/model-interfaces/activities/reject.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APReject = APActivity
+export type APReject = APActivity & { type: "Reject" };
+
+export const ActivityIsReject = (
+	activity: APActivity,
+): activity is APReject => {
+	return activity.type == "Reject";
+};
diff --git a/src/model-interfaces/activities/remove.interface.ts b/src/model-interfaces/activities/remove.interface.ts
index a8b8ca0..594927d 100644
--- a/src/model-interfaces/activities/remove.interface.ts
+++ b/src/model-interfaces/activities/remove.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APRemove = APActivity
+export type APRemove = APActivity & { type: "Remove" };
+
+export const ActivityIsRemove = (
+	activity: APActivity,
+): activity is APRemove => {
+	return activity.type == "Remove";
+};
diff --git a/src/model-interfaces/activities/tentative-accept.interface.ts b/src/model-interfaces/activities/tentative-accept.interface.ts
index 307d1ba..b2ddb3e 100644
--- a/src/model-interfaces/activities/tentative-accept.interface.ts
+++ b/src/model-interfaces/activities/tentative-accept.interface.ts
@@ -1,3 +1,9 @@
-import { APAccept } from './accept.interface';
+import { APActivity } from "./activity.interface";
 
-export type APTentativeAccept = APAccept
+export type APTentativeAccept = APActivity & { type: "TentativeAccept" };
+
+export const ActivityIsTentativeAccept = (
+	activity: APActivity,
+): activity is APTentativeAccept => {
+	return activity.type == "TentativeAccept";
+};
diff --git a/src/model-interfaces/activities/tentative-reject.interface.ts b/src/model-interfaces/activities/tentative-reject.interface.ts
index 4930b0c..0fefd04 100644
--- a/src/model-interfaces/activities/tentative-reject.interface.ts
+++ b/src/model-interfaces/activities/tentative-reject.interface.ts
@@ -1,3 +1,9 @@
-import { APReject } from './reject.interface';
+import { APActivity } from "./activity.interface";
 
-export type APTentativeReject = APReject
+export type APTentativeReject = APActivity & { type: "TentativeReject" };
+
+export const ActivityIsTentativeReject = (
+	activity: APActivity,
+): activity is APTentativeReject => {
+	return activity.type == "TentativeReject";
+};
diff --git a/src/model-interfaces/activities/travel.interface.ts b/src/model-interfaces/activities/travel.interface.ts
index 24f74c5..fad3225 100644
--- a/src/model-interfaces/activities/travel.interface.ts
+++ b/src/model-interfaces/activities/travel.interface.ts
@@ -1,3 +1,9 @@
-import { APIntransitiveActivity } from './intransitive-activity.interface';
+import { APIntransitiveActivity } from "./intransitive-activity.interface";
 
-export type APTravel = APIntransitiveActivity
+export type APTravel = APIntransitiveActivity & { type: "Travel" };
+
+export const ActivityIsTravel = (
+	activity: APIntransitiveActivity,
+): activity is APTravel => {
+	return activity.type == "Travel";
+};
diff --git a/src/model-interfaces/activities/undo.interface.ts b/src/model-interfaces/activities/undo.interface.ts
index b690d67..2d7e7e3 100644
--- a/src/model-interfaces/activities/undo.interface.ts
+++ b/src/model-interfaces/activities/undo.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APUndo = APActivity
+export type APUndo = APActivity & { type: "Undo" };
+
+export const ActivityIsUndo = (activity: APActivity): activity is APUndo => {
+	return activity.type == "Undo";
+};
diff --git a/src/model-interfaces/activities/update.interface.ts b/src/model-interfaces/activities/update.interface.ts
index 438d338..1223bce 100644
--- a/src/model-interfaces/activities/update.interface.ts
+++ b/src/model-interfaces/activities/update.interface.ts
@@ -1,3 +1,9 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APUpdate = APActivity
+export type APUpdate = APActivity & { type: "Update" };
+
+export const ActivityIsUpdate = (
+	activity: APActivity,
+): activity is APUpdate => {
+	return activity.type == "Update";
+};
diff --git a/src/model-interfaces/activities/view.interface.ts b/src/model-interfaces/activities/view.interface.ts
index f081845..baed991 100644
--- a/src/model-interfaces/activities/view.interface.ts
+++ b/src/model-interfaces/activities/view.interface.ts
@@ -1,3 +1,7 @@
-import { APActivity } from './activity.interface';
+import { APActivity } from "./activity.interface";
 
-export type APView = APActivity
+export type APView = APActivity & { type: "View" };
+
+export const ActivityIsView = (activity: APActivity): activity is APView => {
+	return activity.type == "View";
+};
diff --git a/src/model-interfaces/actors/actor.interface.ts b/src/model-interfaces/actors/actor.interface.ts
index e615a36..aa3cda8 100644
--- a/src/model-interfaces/actors/actor.interface.ts
+++ b/src/model-interfaces/actors/actor.interface.ts
@@ -1,111 +1,110 @@
-import { APObject } from '../common/object.interface';
+import { APObject } from "../common/object.interface";
 import {
-    FollowersField,
-    FollowingField,
-    InboxField,
-    LikedField,
-    OutboxField,
-    PreferredUsernameMapField,
-    PreferredUsernameField,
-    StreamsField,
-    EndpointsField
-} from '../../fields';
+	FollowersField,
+	FollowingField,
+	InboxField,
+	LikedField,
+	OutboxField,
+	PreferredUsernameMapField,
+	PreferredUsernameField,
+	StreamsField,
+	EndpointsField,
+} from "../../fields";
 
 export interface APActor extends APObject {
+	/*
+	 *  The inbox is discovered through the inbox property of an actor's profile.
+	 *  The inbox MUST be an OrderedCollection. The inbox stream contains all activities
+	 *  received by the actor. The server SHOULD filter content according to the
+	 *  requester permission. In general, the owner of an inbox is likely to be
+	 *  able to access all of their inbox contents. Depending on access control,
+	 *  some other content may be public, whereas other content may require
+	 *  authentication for non-owner users, if they can access the inbox at all.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#inbox Docs}
+	 */
+	inbox: InboxField;
 
-    /*
-     *  The inbox is discovered through the inbox property of an actor's profile.
-     *  The inbox MUST be an OrderedCollection. The inbox stream contains all activities
-     *  received by the actor. The server SHOULD filter content according to the
-     *  requester permission. In general, the owner of an inbox is likely to be
-     *  able to access all of their inbox contents. Depending on access control,
-     *  some other content may be public, whereas other content may require
-     *  authentication for non-owner users, if they can access the inbox at all.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#inbox Docs}
-     */
-    inbox: InboxField;
-
-    /**
-     *  The outbox is discovered through the outbox property of an actor's profile.
-     *  The outbox MUST be an OrderedCollection. The outbox stream contains activities
-     *  the user has published, subject to the ability of the requester to retrieve the
-     *  activity (that is, the contents of the outbox are filtered by the permissions
-     *  of the person reading it). If a user submits a request without Authorization the
-     *  server should respond with all the Public posts. This could potentially be all
-     *  relevant objects published by the user, though the number of available items is
-     *  left to the discretion of those implementing and deploying the server.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#outbox Docs}
-     */
-    outbox: OutboxField;
+	/**
+	 *  The outbox is discovered through the outbox property of an actor's profile.
+	 *  The outbox MUST be an OrderedCollection. The outbox stream contains activities
+	 *  the user has published, subject to the ability of the requester to retrieve the
+	 *  activity (that is, the contents of the outbox are filtered by the permissions
+	 *  of the person reading it). If a user submits a request without Authorization the
+	 *  server should respond with all the Public posts. This could potentially be all
+	 *  relevant objects published by the user, though the number of available items is
+	 *  left to the discretion of those implementing and deploying the server.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#outbox Docs}
+	 */
+	outbox: OutboxField;
 
-    /**
-     * Every actor SHOULD have a collection of following. This is a list of everybody that
-     * the actor has followed, added as a side effect. The following collection MUST be
-     * either an OrderedCollection or a Collection and MAY be filtered on privileges of an
-     * authenticated user or as appropriate when no authentication is given.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#following Docs}
-     */
-    following?: FollowingField;
+	/**
+	 * Every actor SHOULD have a collection of following. This is a list of everybody that
+	 * the actor has followed, added as a side effect. The following collection MUST be
+	 * either an OrderedCollection or a Collection and MAY be filtered on privileges of an
+	 * authenticated user or as appropriate when no authentication is given.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#following Docs}
+	 */
+	following?: FollowingField;
 
-    /**
-     * Every actor SHOULD have a collection of followers. This is a list of everyone who has
-     * sent a Follow activity for the actor, added as a side effect. This is where one would
-     * find a list of all the actors that are following the actor. The followers collection
-     * MUST be either an OrderedCollection or a Collection and MAY be filtered on privileges
-     * of an authenticated user or as appropriate when no authentication is given.
-     *
-     * NOTE: The follow activity generally is a request to see the objects an actor creates.
-     * This makes the Followers collection an appropriate default target for delivery of notifications.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#followers Docs}
-     */
-    followers?: FollowersField;
+	/**
+	 * Every actor SHOULD have a collection of followers. This is a list of everyone who has
+	 * sent a Follow activity for the actor, added as a side effect. This is where one would
+	 * find a list of all the actors that are following the actor. The followers collection
+	 * MUST be either an OrderedCollection or a Collection and MAY be filtered on privileges
+	 * of an authenticated user or as appropriate when no authentication is given.
+	 *
+	 * NOTE: The follow activity generally is a request to see the objects an actor creates.
+	 * This makes the Followers collection an appropriate default target for delivery of notifications.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#followers Docs}
+	 */
+	followers?: FollowersField;
 
-    /**
-     * Every actor MAY have a liked collection. This is a list of every object from all the
-     * actor's Like activities, added as a side effect. The liked collection MUST be either
-     * an OrderedCollection or a Collection and MAY be filtered on privileges of an
-     * authenticated user or as appropriate when no authentication is given.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#liked Docs}
-     */
-    liked?: LikedField;
+	/**
+	 * Every actor MAY have a liked collection. This is a list of every object from all the
+	 * actor's Like activities, added as a side effect. The liked collection MUST be either
+	 * an OrderedCollection or a Collection and MAY be filtered on privileges of an
+	 * authenticated user or as appropriate when no authentication is given.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#liked Docs}
+	 */
+	liked?: LikedField;
 
-    /**
-     * A list of supplementary Collections which may be of interest.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#actors Docs}
-     */
-    streams?: StreamsField | StreamsField[];
+	/**
+	 * A list of supplementary Collections which may be of interest.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#actors Docs}
+	 */
+	streams?: StreamsField | StreamsField[];
 
-    /**
-     * A short username which may be used to refer to the actor, with no uniqueness guarantees.
-     * [For multiple language-tagged values use preferredUsernameMap property]
-     *
-     * {@link https://www.w3.org/TR/activitypub/#actors Docs}
-     */
-    preferredUsername?: PreferredUsernameField;
+	/**
+	 * A short username which may be used to refer to the actor, with no uniqueness guarantees.
+	 * [For multiple language-tagged values use preferredUsernameMap property]
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#actors Docs}
+	 */
+	preferredUsername?: PreferredUsernameField;
 
-    /**
-     * A short username which may be used to refer to the actor, with no uniqueness guarantees.
-     * [For a single value use preferredUsername property]
-     *
-     * {@link https://www.w3.org/TR/activitypub/#actors Docs}
-     */
-    preferredUsernameMap?: PreferredUsernameMapField;
+	/**
+	 * A short username which may be used to refer to the actor, with no uniqueness guarantees.
+	 * [For a single value use preferredUsername property]
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#actors Docs}
+	 */
+	preferredUsernameMap?: PreferredUsernameMapField;
 
-    /**
-     * A json object which maps additional (typically server/domain-wide) endpoints which may
-     * be useful either for this actor or someone referencing this actor. This mapping may be
-     * nested inside the actor document as the value or may be a link to a JSON-LD document with
-     * these properties.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#actors Docs}
-     */
-    endpoints?: EndpointsField;
+	/**
+	 * A json object which maps additional (typically server/domain-wide) endpoints which may
+	 * be useful either for this actor or someone referencing this actor. This mapping may be
+	 * nested inside the actor document as the value or may be a link to a JSON-LD document with
+	 * these properties.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#actors Docs}
+	 */
+	endpoints?: EndpointsField;
 
 	/**
 	 * The public key of this actor, used to sign activities.
@@ -117,5 +116,5 @@ export interface APActor extends APObject {
 		owner: string;
 		/** The RSA public key. */
 		publicKeyPem: string;
-	}
+	};
 }
diff --git a/src/model-interfaces/actors/application.interface.ts b/src/model-interfaces/actors/application.interface.ts
index df50008..a7a0ad2 100644
--- a/src/model-interfaces/actors/application.interface.ts
+++ b/src/model-interfaces/actors/application.interface.ts
@@ -1,3 +1,7 @@
-import { APActor } from './actor.interface';
+import { APActor } from "./actor.interface";
 
-export type APApplication = APActor
+export type APApplication = APActor & { type: "Application" };
+
+export const ActorIsApplication = (actor: APActor): actor is APApplication => {
+	return actor.type == "Application";
+};
diff --git a/src/model-interfaces/actors/group.interface.ts b/src/model-interfaces/actors/group.interface.ts
index 6813fb9..d9ece01 100644
--- a/src/model-interfaces/actors/group.interface.ts
+++ b/src/model-interfaces/actors/group.interface.ts
@@ -1,3 +1,7 @@
-import { APActor } from './actor.interface';
+import { APActor } from "./actor.interface";
 
-export type APGroup = APActor
+export type APGroup = APActor & { type: "Group" };
+
+export const ActorIsGroup = (actor: APActor): actor is APGroup => {
+	return actor.type == "Group";
+};
diff --git a/src/model-interfaces/actors/organization.interface.ts b/src/model-interfaces/actors/organization.interface.ts
index ca5ae31..3a39a3a 100644
--- a/src/model-interfaces/actors/organization.interface.ts
+++ b/src/model-interfaces/actors/organization.interface.ts
@@ -1,3 +1,9 @@
-import { APActor } from './actor.interface';
+import { APActor } from "./actor.interface";
 
-export type APOrganization = APActor
\ No newline at end of file
+export type APOrganization = APActor & { type: "Organization" };
+
+export const ActorIsOrganization = (
+	actor: APActor,
+): actor is APOrganization => {
+	return actor.type == "Organization";
+};
diff --git a/src/model-interfaces/actors/person.interface.ts b/src/model-interfaces/actors/person.interface.ts
index 55749ca..01660cc 100644
--- a/src/model-interfaces/actors/person.interface.ts
+++ b/src/model-interfaces/actors/person.interface.ts
@@ -1,3 +1,7 @@
-import { APActor } from './actor.interface';
+import { APActor } from "./actor.interface";
 
-export type APPerson = APActor
\ No newline at end of file
+export type APPerson = APActor & { type: "Person" };
+
+export const ActorIsPerson = (actor: APActor): actor is APPerson => {
+	return actor.type == "Person";
+};
diff --git a/src/model-interfaces/actors/service.interface.ts b/src/model-interfaces/actors/service.interface.ts
index a8620a5..bb436b3 100644
--- a/src/model-interfaces/actors/service.interface.ts
+++ b/src/model-interfaces/actors/service.interface.ts
@@ -1,3 +1,7 @@
-import { APActor } from './actor.interface';
+import { APActor } from "./actor.interface";
 
-export type APService = APActor
\ No newline at end of file
+export type APService = APActor & { type: "Service" };
+
+export const ActorIsService = (actor: APActor): actor is APService => {
+	return actor.type == "Service";
+};
diff --git a/src/model-interfaces/collections/collection-page.interface.ts b/src/model-interfaces/collections/collection-page.interface.ts
index ef54571..0cfef3d 100644
--- a/src/model-interfaces/collections/collection-page.interface.ts
+++ b/src/model-interfaces/collections/collection-page.interface.ts
@@ -1,26 +1,29 @@
-import { APCollection } from './collection.interface';
-import {CollectionPageNextField, CollectionPagePartOfField, CollectionPagePrevField} from '../../fields';
+import { APCollection } from "./collection.interface";
+import {
+	CollectionPageNextField,
+	CollectionPagePartOfField,
+	CollectionPagePrevField,
+} from "../../fields";
 
 export interface APCollectionPage extends APCollection {
+	/**
+	 * Identifies the Collection to which a CollectionPage objects items belong.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#partOf Docs}
+	 */
+	partOf?: CollectionPagePartOfField;
 
-    /**
-     * Identifies the Collection to which a CollectionPage objects items belong.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#partOf Docs}
-     */
-    partOf?: CollectionPagePartOfField;
+	/**
+	 * In a paged Collection, indicates the next page of items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#next Docs}
+	 */
+	next?: CollectionPageNextField;
 
-    /**
-     * In a paged Collection, indicates the next page of items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#next Docs}
-     */
-    next?: CollectionPageNextField;
-
-    /**
-     * In a paged Collection, identifies the previous page of items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#prev Docs}
-     */
-    prev?: CollectionPagePrevField;
+	/**
+	 * In a paged Collection, identifies the previous page of items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#prev Docs}
+	 */
+	prev?: CollectionPagePrevField;
 }
diff --git a/src/model-interfaces/collections/collection.interface.ts b/src/model-interfaces/collections/collection.interface.ts
index 92fa85c..4aa3371 100644
--- a/src/model-interfaces/collections/collection.interface.ts
+++ b/src/model-interfaces/collections/collection.interface.ts
@@ -1,51 +1,51 @@
-import { APObject } from '../common/object.interface';
+import { APObject } from "../common/object.interface";
 import {
-    CollectionCurrentField,
-    CollectionFirstField, CollectionItemsField,
-    CollectionLastField,
-    TotalItemsField
-} from '../../fields';
+	CollectionCurrentField,
+	CollectionFirstField,
+	CollectionItemsField,
+	CollectionLastField,
+	TotalItemsField,
+} from "../../fields";
 
 export interface APCollection extends APObject {
+	/**
+	 * A non-negative integer specifying the total number of objects contained by
+	 * the logical view of the collection. This number might not reflect the actual
+	 * number of items serialized within the Collection object instance.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#totalItems Docs}
+	 */
+	totalItems?: TotalItemsField;
 
-    /**
-     * A non-negative integer specifying the total number of objects contained by
-     * the logical view of the collection. This number might not reflect the actual
-     * number of items serialized within the Collection object instance.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#totalItems Docs}
-     */
-    totalItems?: TotalItemsField;
+	/**
+	 * In a paged Collection, indicates the page that contains
+	 * the most recently updated member items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#current Docs}
+	 */
+	current?: CollectionCurrentField;
 
-    /**
-     * In a paged Collection, indicates the page that contains
-     * the most recently updated member items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#current Docs}
-     */
-    current?: CollectionCurrentField;
+	/**
+	 * In a paged Collection,indicates the furthest proceeding
+	 * page of items in the collection.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#first Docs}
+	 */
+	first?: CollectionFirstField;
 
-    /**
-     * In a paged Collection,indicates the furthest proceeding
-     * page of items in the collection.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#first Docs}
-     */
-    first?: CollectionFirstField;
+	/**
+	 * In a paged Collection, indicates the furthest proceeding
+	 * page of the collection.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#last Docs}
+	 */
+	last?: CollectionLastField;
 
-    /**
-     * In a paged Collection, indicates the furthest proceeding
-     * page of the collection.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#last Docs}
-     */
-    last?: CollectionLastField;
-
-    /**
-     * Identifies the items contained in a collection.
-     * The items might be ordered or unordered.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#items Docs}
-     */
-    items?: CollectionItemsField[];
+	/**
+	 * Identifies the items contained in a collection.
+	 * The items might be ordered or unordered.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#items Docs}
+	 */
+	items?: CollectionItemsField[];
 }
diff --git a/src/model-interfaces/collections/ordered-collection-page.interface.ts b/src/model-interfaces/collections/ordered-collection-page.interface.ts
index c4848ef..2e476b3 100644
--- a/src/model-interfaces/collections/ordered-collection-page.interface.ts
+++ b/src/model-interfaces/collections/ordered-collection-page.interface.ts
@@ -1,38 +1,38 @@
 import {
-    OrderedCollectionPageNextField,
-    OrderedCollectionPagePartOfField,
-    OrderedCollectionPagePrevField,
-    StartIndexField
-} from '../../fields';
-import { APOrderedCollection } from './ordered-collection.interface';
+	OrderedCollectionPageNextField,
+	OrderedCollectionPagePartOfField,
+	OrderedCollectionPagePrevField,
+	StartIndexField,
+} from "../../fields";
+import { APOrderedCollection } from "./ordered-collection.interface";
 
 export interface APOrderedCollectionPage extends APOrderedCollection {
-    /**
-     * Identifies the OrderedCollection to which a OrderedCollectionPage objects items belong.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#partOf Docs}
-     */
-    partOf?: OrderedCollectionPagePartOfField;
+	/**
+	 * Identifies the OrderedCollection to which a OrderedCollectionPage objects items belong.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#partOf Docs}
+	 */
+	partOf?: OrderedCollectionPagePartOfField;
 
-    /**
-     * In a paged OrderedCollection, indicates the next page of items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#next Docs}
-     */
-    next?: OrderedCollectionPageNextField;
+	/**
+	 * In a paged OrderedCollection, indicates the next page of items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#next Docs}
+	 */
+	next?: OrderedCollectionPageNextField;
 
-    /**
-     * In a paged OrderedCollection, identifies the previous page of items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#prev Docs}
-     */
-    prev?: OrderedCollectionPagePrevField;
+	/**
+	 * In a paged OrderedCollection, identifies the previous page of items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#prev Docs}
+	 */
+	prev?: OrderedCollectionPagePrevField;
 
-    /**
-     * A non-negative integer value identifying the relative position
-     * within the logical view of a strictly ordered collection.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#startIndex Docs}
-     */
-    startIndex?: StartIndexField;
+	/**
+	 * A non-negative integer value identifying the relative position
+	 * within the logical view of a strictly ordered collection.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#startIndex Docs}
+	 */
+	startIndex?: StartIndexField;
 }
diff --git a/src/model-interfaces/collections/ordered-collection.interface.ts b/src/model-interfaces/collections/ordered-collection.interface.ts
index 89b9366..e582937 100644
--- a/src/model-interfaces/collections/ordered-collection.interface.ts
+++ b/src/model-interfaces/collections/ordered-collection.interface.ts
@@ -1,50 +1,51 @@
 import {
-    OrderedCollectionCurrentField,
-    OrderedCollectionFirstField, OrderedCollectionItemsField,
-    OrderedCollectionLastField, TotalItemsField
-} from '../../fields';
-import { APObject } from '../common/object.interface';
+	OrderedCollectionCurrentField,
+	OrderedCollectionFirstField,
+	OrderedCollectionItemsField,
+	OrderedCollectionLastField,
+	TotalItemsField,
+} from "../../fields";
+import { APObject } from "../common/object.interface";
 
 export interface APOrderedCollection extends APObject {
+	/**
+	 * A non-negative integer specifying the total number of objects contained by
+	 * the logical view of the collection. This number might not reflect the actual
+	 * number of items serialized within the Collection object instance.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#totalItems Docs}
+	 */
+	totalItems?: TotalItemsField;
 
-    /**
-     * A non-negative integer specifying the total number of objects contained by
-     * the logical view of the collection. This number might not reflect the actual
-     * number of items serialized within the Collection object instance.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#totalItems Docs}
-     */
-    totalItems?: TotalItemsField;
+	/**
+	 * In a paged OrderedCollection, indicates the page that contains
+	 * the most recently updated member items.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#current Docs}
+	 */
+	current?: OrderedCollectionCurrentField;
 
-    /**
-     * In a paged OrderedCollection, indicates the page that contains
-     * the most recently updated member items.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#current Docs}
-     */
-    current?: OrderedCollectionCurrentField;
+	/**
+	 * In a paged OrderedCollection, indicates the furthest proceeding
+	 * page of items in the collection.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#first Docs}
+	 */
+	first?: OrderedCollectionFirstField;
 
-    /**
-     * In a paged OrderedCollection, indicates the furthest proceeding
-     * page of items in the collection.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#first Docs}
-     */
-    first?: OrderedCollectionFirstField;
+	/**
+	 * In a paged OrderedCollection, indicates the furthest proceeding
+	 * page of the collection.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#last Docs}
+	 */
+	last?: OrderedCollectionLastField;
 
-    /**
-     * In a paged OrderedCollection, indicates the furthest proceeding
-     * page of the collection.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#last Docs}
-     */
-    last?: OrderedCollectionLastField;
-
-    /**
-     * Identifies the ordered items contained in a collection.
-     * The items must be ordered.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#orderedItems Docs}
-     */
-    orderedItems?: OrderedCollectionItemsField[];
+	/**
+	 * Identifies the ordered items contained in a collection.
+	 * The items must be ordered.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#orderedItems Docs}
+	 */
+	orderedItems?: OrderedCollectionItemsField[];
 }
diff --git a/src/model-interfaces/common/article.interface.ts b/src/model-interfaces/common/article.interface.ts
index ca4e8ba..ebf9c41 100644
--- a/src/model-interfaces/common/article.interface.ts
+++ b/src/model-interfaces/common/article.interface.ts
@@ -1,3 +1,7 @@
-import {APObject} from './object.interface';
+import { APObject } from "./object.interface";
 
-export type APArticle = APObject
+export type APArticle = APObject & { type: "Article" };
+
+export const ObjectIsArticle = (object: APObject): object is APArticle => {
+	return object.type == "Article";
+};
diff --git a/src/model-interfaces/common/event.interface.ts b/src/model-interfaces/common/event.interface.ts
index 3634e2f..a71864f 100644
--- a/src/model-interfaces/common/event.interface.ts
+++ b/src/model-interfaces/common/event.interface.ts
@@ -1,3 +1,7 @@
-import {APObject} from './object.interface';
+import { APObject } from "./object.interface";
 
-export type APEvent = APObject
+export type APEvent = APObject & { type: "Event" };
+
+export const ObjectIsEvent = (object: APObject): object is APEvent => {
+	return object.type == "Event";
+};
diff --git a/src/model-interfaces/common/link.interface.ts b/src/model-interfaces/common/link.interface.ts
index a49536b..8dd6669 100644
--- a/src/model-interfaces/common/link.interface.ts
+++ b/src/model-interfaces/common/link.interface.ts
@@ -1,95 +1,102 @@
 import {
-    HeightField,
-    HreflangField,
-    HrefField,
-    MediaTypeField,
-    NameMapField,
-    NameField, PreviewField,
-    RelField, TypeField, WidthField
-} from '../../fields';
+	HeightField,
+	HrefField,
+	HreflangField,
+	MediaTypeField,
+	NameField,
+	NameMapField,
+	PreviewField,
+	RelField,
+	TypeField,
+	WidthField,
+} from "../../fields";
+import { APObject } from "./object.interface";
 
 export interface APLink {
+	/**
+	 * Identifies the {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
+	 * type. Multiple values may be specified.
+	 *
+	 * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Docs (@type)}
+	 */
+	type?: TypeField | TypeField[];
 
-    /**
-     * Identifies the {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
-     * type. Multiple values may be specified.
-     *
-     * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Docs (@type)}
-     */
-    type?: TypeField | TypeField[];
+	/**
+	 * A simple, human-readable, plain-text name for the object.
+	 * HTML markup MUST NOT be included.
+	 * [For multiple language-tagged values use nameMap property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#name Docs}
+	 */
+	name?: NameField;
 
-    /**
-     * A simple, human-readable, plain-text name for the object.
-     * HTML markup MUST NOT be included.
-     * [For multiple language-tagged values use nameMap property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#name Docs}
-     */
-    name?: NameField;
+	/**
+	 * A simple, human-readable, plain-text name for the object.
+	 * HTML markup MUST NOT be included.
+	 * [For a single value use name property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#name Docs}
+	 */
+	nameMap?: NameMapField;
 
-    /**
-     * A simple, human-readable, plain-text name for the object.
-     * HTML markup MUST NOT be included.
-     * [For a single value use name property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#name Docs}
-     */
-    nameMap?: NameMapField;
+	/**
+	 * The target resource pointed to by a Link.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#href Docs}
+	 */
+	href?: HrefField;
 
-    /**
-     * The target resource pointed to by a Link.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#href Docs}
-     */
-    href?: HrefField;
+	/**
+	 * Hints as to the language used by the target resource.
+	 * Field MUST be a [BCP47] Language-Tag.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#hreflang Docs}
+	 */
+	hreflang?: HreflangField;
 
-    /**
-     * Hints as to the language used by the target resource.
-     * Field MUST be a [BCP47] Language-Tag.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#hreflang Docs}
-     */
-    hreflang?: HreflangField;
+	/**
+	 * When used on a Link, identifies the MIME media type of the referenced resource
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#mediaType Docs}
+	 */
+	mediaType?: MediaTypeField;
 
-    /**
-     * When used on a Link, identifies the MIME media type of the referenced resource
-     *
-     * {@link https://www.w3.org/ns/activitystreams#mediaType Docs}
-     */
-    mediaType?: MediaTypeField;
+	/**
+	 * A link relation associated with a Link. The value MUST conform to both
+	 * the [HTML5] and [RFC5988] "link relation" definitions. In the [HTML5],
+	 * any string not containing the "space" U+0020, "tab" (U+0009), "LF" (U+000A), "FF" (U+000C), "CR" (U+000D) or "," (U+002C)
+	 * characters can be used as a valid link relation.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#rel Docs}
+	 */
+	rel?: RelField | RelField[];
 
-    /**
-     * A link relation associated with a Link. The value MUST conform to both
-     * the [HTML5] and [RFC5988] "link relation" definitions. In the [HTML5],
-     * any string not containing the "space" U+0020, "tab" (U+0009), "LF" (U+000A), "FF" (U+000C), "CR" (U+000D) or "," (U+002C)
-     * characters can be used as a valid link relation.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#rel Docs}
-     */
-    rel?: RelField | RelField[];
+	/**
+	 * On a Link, specifies a hint as to the rendering height in
+	 * device-independent pixels of the linked resource.
+	 * Type: Non negative integer
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#height Docs}
+	 */
+	height?: HeightField;
 
-    /**
-     * On a Link, specifies a hint as to the rendering height in
-     * device-independent pixels of the linked resource.
-     * Type: Non negative integer
-     *
-     * {@link https://www.w3.org/ns/activitystreams#height Docs}
-     */
-    height?: HeightField;
+	/**
+	 * On a Link, specifies a hint as to the rendering width in
+	 * device-independent pixels of the linked resource.
+	 * Type: Non negative integer
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#width Docs}
+	 */
+	width?: WidthField;
 
-    /**
-     * On a Link, specifies a hint as to the rendering width in
-     * device-independent pixels of the linked resource.
-     * Type: Non negative integer
-     *
-     * {@link https://www.w3.org/ns/activitystreams#width Docs}
-     */
-    width?: WidthField;
-
-    /**
-     * Identifies an entity that provides a preview of this object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#preview Docs}
-     */
-    preview?: PreviewField;
+	/**
+	 * Identifies an entity that provides a preview of this object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#preview Docs}
+	 */
+	preview?: PreviewField;
 }
+
+export const ObjectIsLink = (object: APObject): object is APLink => {
+	return object.type == "Link";
+};
diff --git a/src/model-interfaces/common/mention.interface.ts b/src/model-interfaces/common/mention.interface.ts
index 1ad1837..5181486 100644
--- a/src/model-interfaces/common/mention.interface.ts
+++ b/src/model-interfaces/common/mention.interface.ts
@@ -1,3 +1,8 @@
-import {APLink} from './link.interface';
+import { APLink } from "./link.interface";
+import { APObject } from "./object.interface";
 
-export type APMention = APLink
+export type APMention = APLink & { type: "Mention" };
+
+export const ObjectIsMention = (object: APObject): object is APMention => {
+	return object.type == "Mention";
+};
diff --git a/src/model-interfaces/common/note.interface.ts b/src/model-interfaces/common/note.interface.ts
index ec17b72..d0c27d4 100644
--- a/src/model-interfaces/common/note.interface.ts
+++ b/src/model-interfaces/common/note.interface.ts
@@ -1,3 +1,7 @@
-import { APObject } from './object.interface';
+import { APObject } from "./object.interface";
 
-export type APNote = APObject
\ No newline at end of file
+export type APNote = APObject & { type: "Note" };
+
+export const ObjectIsNote = (object: APObject): object is APNote => {
+	return object.type == "Note";
+};
diff --git a/src/model-interfaces/common/object.interface.ts b/src/model-interfaces/common/object.interface.ts
index d6e458a..019df58 100644
--- a/src/model-interfaces/common/object.interface.ts
+++ b/src/model-interfaces/common/object.interface.ts
@@ -1,366 +1,369 @@
 import {
-    UrlField,
-    IconField,
-    ImageField,
-    AttachmentField,
-    AudienceField,
-    InReplyToField,
-    LocationField,
-    PreviewField,
-    ToField,
-    BtoField,
-    CcField,
-    BccField,
-    AttributedToField,
-    TagField,
-    GeneratorField,
-    IdField,
-    TypeField,
-    ContentField,
-    ContentMapField,
-    MediaTypeField,
-    NameField,
-    NameMapField,
-    EndTimeField,
-    StartTimeField,
-    PublishedField,
-    RepliesField,
-    SummaryField,
-    SummaryMapField,
-    UpdatedField,
-    DurationField, SourceField, LikesField, SharesField, ContextField,
-} from '../../fields';
+	AttachmentField,
+	AttributedToField,
+	AudienceField,
+	BccField,
+	BtoField,
+	CcField,
+	ContentField,
+	ContentMapField,
+	ContextField,
+	DurationField,
+	EndTimeField,
+	GeneratorField,
+	IconField,
+	IdField,
+	ImageField,
+	InReplyToField,
+	LikesField,
+	LocationField,
+	MediaTypeField,
+	NameField,
+	NameMapField,
+	PreviewField,
+	PublishedField,
+	RepliesField,
+	SharesField,
+	SourceField,
+	StartTimeField,
+	SummaryField,
+	SummaryMapField,
+	TagField,
+	ToField,
+	TypeField,
+	UpdatedField,
+	UrlField,
+} from "../../fields";
 
 export interface APObject {
-    /**
-     * JSON-LD uses the special @context property to define the processing context.
-     * The Field of the @context property is defined by the [JSON-LD] specification.
-     *
-     * {@link https://www.w3.org/TR/activitystreams-core/#jsonld Docs}
-     */
-    '@context'?: ContextField | ContextField[];
-
-    /**
-     * Provides the globally unique identifier for
-     * an {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
-     * All objects must have unique global identifier (unless the object is transient,
-     * in which case the id MAY be omitted).
-     *
-     * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object AS Docs (@id)}
-     *
-     * {@link https://www.w3.org/TR/activitypub/#obj-id AP Docs}
-     */
-    id?: IdField;
-
-    /**
-     * Identifies the {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
-     * type. Multiple values may be specified.
-     * All objects must have type. There is already a bunch of default types presented by this library.
-     *
-     * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object AS Docs (@type)}
-     *
-     * {@link https://www.w3.org/TR/activitypub/#obj-id AP Docs}
-     */
-    type?: TypeField | TypeField[];
-
-    /**
-     * Identifies resources attached or related to an object that potentially requires special handling.
-     * The intent is to provide a model that is at least semantically similar to attachments in email.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#attachment Docs}
-     */
-    attachment?: AttachmentField | AttachmentField[];
-
-
-    /**
-     * Identifies one or more entities to which this object is attributed.
-     * The attributed entities might not be Actors. For instance,
-     * an object might be attributed to the completion of another activity.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#attributedTo Docs}
-     */
-    attributedTo?: AttributedToField | AttributedToField[];
-
-    /**
-     * Identifies one or more entities that represent the total population of entities
-     * for which the object can be considered to be relevant.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#audience Docs}
-     */
-    audience?: AudienceField | AudienceField[];
-
-    /**
-     * The content or textual representation of the Object encoded as a JSON string.
-     * By default, the value of content is HTML. The mediaType property can be
-     * used in the object to indicate a different content type.
-     * [For multiple language-tagged values use contentMap property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#content Docs}
-     */
-    content?: ContentField;
-
-    /**
-     * The content or textual representation of the Object encoded as a JSON string.
-     * By default, the value of content is HTML. The mediaType property can be
-     * used in the object to indicate a different content type.
-     * [For a single value use content property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#content Docs}
-     */
-    contentMap?: ContentMapField;
-
-    /**
-     * When used on an Object, identifies the MIME media type of the value of the content property.
-     * If not specified, the content property is assumed to contain text/html content.
-     * Works different with Link
-     *
-     * {@link https://www.w3.org/ns/activitystreams#mediaType Docs}
-     */
-    mediaType?: MediaTypeField;
-
-    /**
-     * A simple, human-readable, plain-text name for the object.
-     * HTML markup MUST NOT be included.
-     * [For multiple language-tagged values use nameMap property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#name Docs}
-     */
-    name?: NameField;
-
-    /**
-     * A simple, human-readable, plain-text name for the object.
-     * HTML markup MUST NOT be included.
-     * [For a single value use name property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#name Docs}
-     */
-    nameMap?: NameMapField;
-
-    /**
-     * The date and time describing the actual or expected ending time of the object.
-     * When used with an Activity object, for instance, the endTime property specifies
-     * the moment the activity concluded or is expected to conclude.
-     *
-     * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
-     *
-     * {@link https://www.w3.org/ns/activitystreams#endTime Docs}
-     *
-     * @example
-     * 2020-08-08T08:30:11-03:00Z
-     * 2020-08-08T08:30:11-03:00
-     * 2020-08-08T08:30:11Z
-     * 2020-08-08T08:30:11
-     * 2020-08-08
-     */
-    endTime?: EndTimeField;
-
-    /**
-     * The date and time describing the actual or expected starting time of the object.
-     * When used with an Activity object, for instance, the startTime property specifies
-     * the moment the activity began or is scheduled to begin.
-     *
-     * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
-     *
-     * {@link https://www.w3.org/ns/activitystreams#startTime Docs}
-     *
-     * @example
-     * 2020-08-08T08:30:11-03:00Z
-     * 2020-08-08T08:30:11-03:00
-     * 2020-08-08T08:30:11Z
-     * 2020-08-08T08:30:11
-     * 2020-08-08
-     */
-    startTime?: StartTimeField;
-
-    /**
-     * Identifies the entity (e.g. an application) that generated the object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#generator Docs}
-     */
-    generator?: GeneratorField;
-
-    /**
-     * Indicates an entity (or entities) that describes an icon for this object.
-     * Unlike image property, the icon should have an aspect ratio of one (horizontal)
-     * to one (vertical) and should be suitable for presentation at a small size.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#icon Docs}
-     */
-    icon?: IconField | IconField[];
-
-    /**
-     * Indicates an entity that describes an image for this object.
-     * Unlike the icon property, there are no aspect ratio or display size limitations assumed.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#image Docs}
-     */
-    image?: ImageField | ImageField[];
-
-    /**
-     * Indicates one or more entities for which this object is considered a response.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#inReplyTo Docs}
-     */
-    inReplyTo?: InReplyToField | InReplyToField[];
-
-    /**
-     * Indicates one or more physical or logical locations associated with the object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#location Docs}
-     */
-    location?: LocationField | LocationField[];
-
-    /**
-     * Identifies an entity that provides a preview of this object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#preview Docs}
-     */
-    preview?: PreviewField;
-
-    /**
-     * The date and time at which the object was published.
-     *
-     * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
-     *
-     * {@link https://www.w3.org/ns/activitystreams#published Docs}
-     *
-     * @example
-     * 2020-08-08T08:30:11-03:00Z
-     * 2020-08-08T08:30:11-03:00
-     * 2020-08-08T08:30:11Z
-     * 2020-08-08T08:30:11
-     * 2020-08-08
-     */
-    published?: PublishedField;
-
-    /**
-     * Identifies a Collection containing objects considered to be responses to this object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#replies Docs}
-     */
-    replies?: RepliesField;
-
-    /**
-     * A natural language summarization of the object encoded as HTML.
-     * Multiple language tagged summaries MAY be provided.
-     * [For multiple language-tagged values use summaryMap property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#summary Docs}
-     */
-    summary?: SummaryField;
-
-    /**
-     * A natural language summarization of the object encoded as HTML.
-     * Multiple language tagged summaries MAY be provided.
-     * [For a single value use summary property]
-     *
-     * {@link https://www.w3.org/ns/activitystreams#summary Docs}
-     */
-    summaryMap?: SummaryMapField;
-
-    /**
-     * One or more "tags" that have been associated with an objects. A tag can be any kind of Object.
-     * The key difference between attachment and tag is that the former implies association by
-     * inclusion, while the latter implies associated by reference.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#tag Docs}
-     */
-    tag?: TagField | TagField[];
-
-    /**
-     * The date and time at which the object was updated.
-     *
-     * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
-     *
-     * {@link https://www.w3.org/ns/activitystreams#published Docs}
-     *
-     * @example
-     * 2020-08-08T08:30:11-03:00Z
-     * 2020-08-08T08:30:11-03:00
-     * 2020-08-08T08:30:11Z
-     * 2020-08-08T08:30:11
-     * 2020-08-08
-     */
-    updated?: UpdatedField;
-
-    /**
-     * Identifies one or more links to representations of the object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#url Docs}
-     */
-    url?: UrlField | UrlField[];
-
-    /**
-     * Identifies an entity or entities considered to be part of the public primary audience of an Object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#to Docs}
-     */
-    to?: ToField | ToField[];
-
-    /**
-     * Identifies an Object that is part of the private primary audience of this Object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#bto Docs}
-     */
-    bto?: BtoField | BtoField[];
-
-    /**
-     * Identifies an Object that is part of the public secondary audience of this Object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#cc Docs}
-     */
-    cc?: CcField | CcField[];
-
-    /**
-     * Identifies one or more Objects that are part of the private secondary audience of this Object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#bcc Docs}
-     */
-    bcc?: BccField | BccField[];
-
-    /**
-     * When the object describes a time-bound resource, such as an audio or video, a meeting, etc.,
-     * the duration property indicates the object's approximate duration.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#duration Docs}
-     *
-     * Must be provided in {@link http://www.datypic.com/sc/xsd/t-xsd_duration.html xsd:duration}
-     *
-     * @example
-     * PT20M (20 minutes)
-     * P1DT2H (1 day, 2 hours)
-     * P2Y6M5DT12H35M30S (2 years, 6 months, 5 days, 12 hours, 35 minutes, 30 seconds)
-     */
-    duration?: DurationField;
-
-    /**
-     * ActivityPub extends the Object by supplying the source property. The source property is intended to
-     * convey some sort of source from which the content markup was derived, as a form of provenance, or to
-     * support future editing by clients. In general, clients do the conversion from source to content, not
-     * the other way around.
-     * The value of source is itself an object which uses its own content and mediaType fields to supply source information.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#source-property Docs}
-     */
-    source?: SourceField;
-
-    /**
-     * Every object MAY have a "likes" collection. This is a list of all Like activities with this object as
-     * the object property, added as a side effect. The likes collection MUST be either an OrderedCollection
-     * or a Collection and MAY be filtered on privileges of an authenticated user or as appropriate when
-     * no authentication is given.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#likes Docs}
-     */
-    likes?: LikesField;
-
-    /**
-     * Every object MAY have a "shares" collection. This is a list of all Announce activities with this object as
-     * the object property, added as a side effect. The shares collection MUST be either an OrderedCollection
-     * or a Collection and MAY be filtered on privileges of an authenticated user or as appropriate when
-     * no authentication is given.
-     *
-     * {@link https://www.w3.org/TR/activitypub/#shares Docs}
-     */
-    shares?: SharesField;
-}
\ No newline at end of file
+	/**
+	 * JSON-LD uses the special @context property to define the processing context.
+	 * The Field of the @context property is defined by the [JSON-LD] specification.
+	 *
+	 * {@link https://www.w3.org/TR/activitystreams-core/#jsonld Docs}
+	 */
+	"@context"?: ContextField | ContextField[];
+
+	/**
+	 * Provides the globally unique identifier for
+	 * an {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
+	 * All objects must have unique global identifier (unless the object is transient,
+	 * in which case the id MAY be omitted).
+	 *
+	 * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object AS Docs (@id)}
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#obj-id AP Docs}
+	 */
+	id?: IdField;
+
+	/**
+	 * Identifies the {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object Object}
+	 * type. Multiple values may be specified.
+	 * All objects must have type. There is already a bunch of default types presented by this library.
+	 *
+	 * {@link https://www.w3.org/TR/activitystreams-vocabulary/#dfn-object AS Docs (@type)}
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#obj-id AP Docs}
+	 */
+	type?: TypeField | TypeField[];
+
+	/**
+	 * Identifies resources attached or related to an object that potentially requires special handling.
+	 * The intent is to provide a model that is at least semantically similar to attachments in email.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#attachment Docs}
+	 */
+	attachment?: AttachmentField | AttachmentField[];
+
+	/**
+	 * Identifies one or more entities to which this object is attributed.
+	 * The attributed entities might not be Actors. For instance,
+	 * an object might be attributed to the completion of another activity.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#attributedTo Docs}
+	 */
+	attributedTo?: AttributedToField | AttributedToField[];
+
+	/**
+	 * Identifies one or more entities that represent the total population of entities
+	 * for which the object can be considered to be relevant.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#audience Docs}
+	 */
+	audience?: AudienceField | AudienceField[];
+
+	/**
+	 * The content or textual representation of the Object encoded as a JSON string.
+	 * By default, the value of content is HTML. The mediaType property can be
+	 * used in the object to indicate a different content type.
+	 * [For multiple language-tagged values use contentMap property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#content Docs}
+	 */
+	content?: ContentField;
+
+	/**
+	 * The content or textual representation of the Object encoded as a JSON string.
+	 * By default, the value of content is HTML. The mediaType property can be
+	 * used in the object to indicate a different content type.
+	 * [For a single value use content property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#content Docs}
+	 */
+	contentMap?: ContentMapField;
+
+	/**
+	 * When used on an Object, identifies the MIME media type of the value of the content property.
+	 * If not specified, the content property is assumed to contain text/html content.
+	 * Works different with Link
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#mediaType Docs}
+	 */
+	mediaType?: MediaTypeField;
+
+	/**
+	 * A simple, human-readable, plain-text name for the object.
+	 * HTML markup MUST NOT be included.
+	 * [For multiple language-tagged values use nameMap property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#name Docs}
+	 */
+	name?: NameField;
+
+	/**
+	 * A simple, human-readable, plain-text name for the object.
+	 * HTML markup MUST NOT be included.
+	 * [For a single value use name property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#name Docs}
+	 */
+	nameMap?: NameMapField;
+
+	/**
+	 * The date and time describing the actual or expected ending time of the object.
+	 * When used with an Activity object, for instance, the endTime property specifies
+	 * the moment the activity concluded or is expected to conclude.
+	 *
+	 * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#endTime Docs}
+	 *
+	 * @example
+	 * 2020-08-08T08:30:11-03:00Z
+	 * 2020-08-08T08:30:11-03:00
+	 * 2020-08-08T08:30:11Z
+	 * 2020-08-08T08:30:11
+	 * 2020-08-08
+	 */
+	endTime?: EndTimeField;
+
+	/**
+	 * The date and time describing the actual or expected starting time of the object.
+	 * When used with an Activity object, for instance, the startTime property specifies
+	 * the moment the activity began or is scheduled to begin.
+	 *
+	 * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#startTime Docs}
+	 *
+	 * @example
+	 * 2020-08-08T08:30:11-03:00Z
+	 * 2020-08-08T08:30:11-03:00
+	 * 2020-08-08T08:30:11Z
+	 * 2020-08-08T08:30:11
+	 * 2020-08-08
+	 */
+	startTime?: StartTimeField;
+
+	/**
+	 * Identifies the entity (e.g. an application) that generated the object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#generator Docs}
+	 */
+	generator?: GeneratorField;
+
+	/**
+	 * Indicates an entity (or entities) that describes an icon for this object.
+	 * Unlike image property, the icon should have an aspect ratio of one (horizontal)
+	 * to one (vertical) and should be suitable for presentation at a small size.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#icon Docs}
+	 */
+	icon?: IconField | IconField[];
+
+	/**
+	 * Indicates an entity that describes an image for this object.
+	 * Unlike the icon property, there are no aspect ratio or display size limitations assumed.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#image Docs}
+	 */
+	image?: ImageField | ImageField[];
+
+	/**
+	 * Indicates one or more entities for which this object is considered a response.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#inReplyTo Docs}
+	 */
+	inReplyTo?: InReplyToField | InReplyToField[];
+
+	/**
+	 * Indicates one or more physical or logical locations associated with the object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#location Docs}
+	 */
+	location?: LocationField | LocationField[];
+
+	/**
+	 * Identifies an entity that provides a preview of this object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#preview Docs}
+	 */
+	preview?: PreviewField;
+
+	/**
+	 * The date and time at which the object was published.
+	 *
+	 * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#published Docs}
+	 *
+	 * @example
+	 * 2020-08-08T08:30:11-03:00Z
+	 * 2020-08-08T08:30:11-03:00
+	 * 2020-08-08T08:30:11Z
+	 * 2020-08-08T08:30:11
+	 * 2020-08-08
+	 */
+	published?: PublishedField;
+
+	/**
+	 * Identifies a Collection containing objects considered to be responses to this object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#replies Docs}
+	 */
+	replies?: RepliesField;
+
+	/**
+	 * A natural language summarization of the object encoded as HTML.
+	 * Multiple language tagged summaries MAY be provided.
+	 * [For multiple language-tagged values use summaryMap property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#summary Docs}
+	 */
+	summary?: SummaryField;
+
+	/**
+	 * A natural language summarization of the object encoded as HTML.
+	 * Multiple language tagged summaries MAY be provided.
+	 * [For a single value use summary property]
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#summary Docs}
+	 */
+	summaryMap?: SummaryMapField;
+
+	/**
+	 * One or more "tags" that have been associated with an objects. A tag can be any kind of Object.
+	 * The key difference between attachment and tag is that the former implies association by
+	 * inclusion, while the latter implies associated by reference.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#tag Docs}
+	 */
+	tag?: TagField | TagField[];
+
+	/**
+	 * The date and time at which the object was updated.
+	 *
+	 * Must be provided in {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#published Docs}
+	 *
+	 * @example
+	 * 2020-08-08T08:30:11-03:00Z
+	 * 2020-08-08T08:30:11-03:00
+	 * 2020-08-08T08:30:11Z
+	 * 2020-08-08T08:30:11
+	 * 2020-08-08
+	 */
+	updated?: UpdatedField;
+
+	/**
+	 * Identifies one or more links to representations of the object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#url Docs}
+	 */
+	url?: UrlField | UrlField[];
+
+	/**
+	 * Identifies an entity or entities considered to be part of the public primary audience of an Object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#to Docs}
+	 */
+	to?: ToField | ToField[];
+
+	/**
+	 * Identifies an Object that is part of the private primary audience of this Object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#bto Docs}
+	 */
+	bto?: BtoField | BtoField[];
+
+	/**
+	 * Identifies an Object that is part of the public secondary audience of this Object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#cc Docs}
+	 */
+	cc?: CcField | CcField[];
+
+	/**
+	 * Identifies one or more Objects that are part of the private secondary audience of this Object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#bcc Docs}
+	 */
+	bcc?: BccField | BccField[];
+
+	/**
+	 * When the object describes a time-bound resource, such as an audio or video, a meeting, etc.,
+	 * the duration property indicates the object's approximate duration.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#duration Docs}
+	 *
+	 * Must be provided in {@link http://www.datypic.com/sc/xsd/t-xsd_duration.html xsd:duration}
+	 *
+	 * @example
+	 * PT20M (20 minutes)
+	 * P1DT2H (1 day, 2 hours)
+	 * P2Y6M5DT12H35M30S (2 years, 6 months, 5 days, 12 hours, 35 minutes, 30 seconds)
+	 */
+	duration?: DurationField;
+
+	/**
+	 * ActivityPub extends the Object by supplying the source property. The source property is intended to
+	 * convey some sort of source from which the content markup was derived, as a form of provenance, or to
+	 * support future editing by clients. In general, clients do the conversion from source to content, not
+	 * the other way around.
+	 * The value of source is itself an object which uses its own content and mediaType fields to supply source information.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#source-property Docs}
+	 */
+	source?: SourceField;
+
+	/**
+	 * Every object MAY have a "likes" collection. This is a list of all Like activities with this object as
+	 * the object property, added as a side effect. The likes collection MUST be either an OrderedCollection
+	 * or a Collection and MAY be filtered on privileges of an authenticated user or as appropriate when
+	 * no authentication is given.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#likes Docs}
+	 */
+	likes?: LikesField;
+
+	/**
+	 * Every object MAY have a "shares" collection. This is a list of all Announce activities with this object as
+	 * the object property, added as a side effect. The shares collection MUST be either an OrderedCollection
+	 * or a Collection and MAY be filtered on privileges of an authenticated user or as appropriate when
+	 * no authentication is given.
+	 *
+	 * {@link https://www.w3.org/TR/activitypub/#shares Docs}
+	 */
+	shares?: SharesField;
+}
diff --git a/src/model-interfaces/common/place.interface.ts b/src/model-interfaces/common/place.interface.ts
index 51ea944..ab71d8b 100644
--- a/src/model-interfaces/common/place.interface.ts
+++ b/src/model-interfaces/common/place.interface.ts
@@ -1,60 +1,64 @@
-import {APObject} from './object.interface';
 import {
-    AccuracyField,
-    AltitudeField,
-    LatitudeField,
-    LongitudeField,
-    RadiusField,
-    UnitsField
-} from '../../fields';
-
+	AccuracyField,
+	AltitudeField,
+	LatitudeField,
+	LongitudeField,
+	RadiusField,
+	UnitsField,
+} from "../../fields";
+import { APObject } from "./object.interface";
 
 export interface APPlace extends APObject {
+	type: "Place";
+
+	/**
+	 * Indicates the accuracy of position coordinates on a Place objects.
+	 * Expressed in properties of percentage. e.g. "94.0" means "94.0% accurate".
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#accuracy Docs}
+	 */
+	accuracy?: AccuracyField;
+
+	/**
+	 * Indicates the altitude of a place. The measurement units is indicated using the "units" property.
+	 * If units is not specified, the default is assumed to be "m" indicating "meters".
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#altitude Docs}
+	 */
+	altitude?: AltitudeField;
+
+	/**
+	 * The latitude of a place
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#latitude Docs}
+	 */
+	latitude?: LatitudeField;
 
-    /**
-     * Indicates the accuracy of position coordinates on a Place objects.
-     * Expressed in properties of percentage. e.g. "94.0" means "94.0% accurate".
-     *
-     * {@link https://www.w3.org/ns/activitystreams#accuracy Docs}
-     */
-    accuracy?: AccuracyField;
-
-    /**
-     * Indicates the altitude of a place. The measurement units is indicated using the "units" property.
-     * If units is not specified, the default is assumed to be "m" indicating "meters".
-     *
-     * {@link https://www.w3.org/ns/activitystreams#altitude Docs}
-     */
-    altitude?: AltitudeField;
-
-    /**
-     * The latitude of a place
-     *
-     * {@link https://www.w3.org/ns/activitystreams#latitude Docs}
-     */
-    latitude?: LatitudeField;
-
-    /**
-     * The longitude of a place
-     *
-     * {@link https://www.w3.org/ns/activitystreams#longitude Docs}
-     */
-    longitude?: LongitudeField;
-
-    /**
-     * The radius from the given latitude and longitude for a Place.
-     * The units are expressed by the "units" property. If units is not specified,
-     * the default is assumed to be "m" indicating "meters".
-     *
-     * {@link https://www.w3.org/ns/activitystreams#radius Docs}
-     */
-    radius?: RadiusField;
-
-    /**
-     * Specifies the measurement units for the radius and altitude properties
-     * on a Place object. If not specified, the default is assumed to be "m" for "meters".
-     *
-     * {@link https://www.w3.org/ns/activitystreams#units Docs}
-     */
-    units?: UnitsField;
+	/**
+	 * The longitude of a place
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#longitude Docs}
+	 */
+	longitude?: LongitudeField;
+
+	/**
+	 * The radius from the given latitude and longitude for a Place.
+	 * The units are expressed by the "units" property. If units is not specified,
+	 * the default is assumed to be "m" indicating "meters".
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#radius Docs}
+	 */
+	radius?: RadiusField;
+
+	/**
+	 * Specifies the measurement units for the radius and altitude properties
+	 * on a Place object. If not specified, the default is assumed to be "m" for "meters".
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#units Docs}
+	 */
+	units?: UnitsField;
 }
+
+export const ObjectIsPlace = (object: APObject): object is APPlace => {
+	return object.type == "Place";
+};
diff --git a/src/model-interfaces/common/profile.interface.ts b/src/model-interfaces/common/profile.interface.ts
index 06da25f..849587a 100644
--- a/src/model-interfaces/common/profile.interface.ts
+++ b/src/model-interfaces/common/profile.interface.ts
@@ -1,13 +1,18 @@
-import {DescribesField} from '../../fields';
-import { APObject } from './object.interface';
+import { DescribesField } from "../../fields";
+import { APObject } from "./object.interface";
 
 export interface APProfile extends APObject {
+	type: "Profile";
 
-    /**
-     * On a Profile object, the describes property identifies
-     * the object described by the Profile.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#describes Docs}
-     */
-    describes?: DescribesField;
+	/**
+	 * On a Profile object, the describes property identifies
+	 * the object described by the Profile.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#describes Docs}
+	 */
+	describes?: DescribesField;
 }
+
+export const ObjectIsProfile = (object: APObject): object is APProfile => {
+	return object.type == "Profile";
+};
diff --git a/src/model-interfaces/common/relationship.interface.ts b/src/model-interfaces/common/relationship.interface.ts
index 16475f4..c82f091 100644
--- a/src/model-interfaces/common/relationship.interface.ts
+++ b/src/model-interfaces/common/relationship.interface.ts
@@ -1,29 +1,36 @@
-import {SubjectField, ObjectField, RelationshipField} from '../../fields';
-import { APObject } from './object.interface';
+import { ObjectField, RelationshipField, SubjectField } from "../../fields";
+import { APObject } from "./object.interface";
 
 export interface APRelationship extends APObject {
+	type: "Relationship";
 
-    /**
-     * On a Relationship object, the subject property identifies one of the connected individuals.
-     * For instance, for a Relationship object describing "John is related to Sally",
-     * subject would refer to John.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#subject Docs}
-     */
-    subject?: SubjectField;
+	/**
+	 * On a Relationship object, the subject property identifies one of the connected individuals.
+	 * For instance, for a Relationship object describing "John is related to Sally",
+	 * subject would refer to John.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#subject Docs}
+	 */
+	subject?: SubjectField;
 
-    /**
-     * When used within a Relationship describes the entity to which the subject is related.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#object Docs}
-     */
-    object?: ObjectField | ObjectField[];
+	/**
+	 * When used within a Relationship describes the entity to which the subject is related.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#object Docs}
+	 */
+	object?: ObjectField | ObjectField[];
 
-    /**
-     * On a Relationship object, the relationship property
-     * identifies the kind of relationship that exists between subject and object.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#relationship Docs}
-     */
-    relationship?: RelationshipField;
+	/**
+	 * On a Relationship object, the relationship property
+	 * identifies the kind of relationship that exists between subject and object.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#relationship Docs}
+	 */
+	relationship?: RelationshipField;
 }
+
+export const ObjectIsRelationship = (
+	object: APObject,
+): object is APRelationship => {
+	return object.type == "Relationship";
+};
diff --git a/src/model-interfaces/common/tombstone.interface.ts b/src/model-interfaces/common/tombstone.interface.ts
index 3fd5e4b..4df00fa 100644
--- a/src/model-interfaces/common/tombstone.interface.ts
+++ b/src/model-interfaces/common/tombstone.interface.ts
@@ -1,23 +1,28 @@
-import {DeletedField, FormerTypeField} from '../../fields';
-import { APObject } from './object.interface';
+import { DeletedField, FormerTypeField } from "../../fields";
+import { APObject } from "./object.interface";
 
 export interface APTombstone extends APObject {
+	type: "Tombstone";
 
-    /**
-     * On a Tombstone object, the formerType property identifies
-     * the type of the object that was deleted.
-     *
-     * {@link https://www.w3.org/ns/activitystreams#formerType  Docs}
-     */
-    formerType?: FormerTypeField;
+	/**
+	 * On a Tombstone object, the formerType property identifies
+	 * the type of the object that was deleted.
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#formerType  Docs}
+	 */
+	formerType?: FormerTypeField;
 
-    /**
-     * On a Tombstone object, the deleted property is a timestamp
-     * for when the object was deleted.
-     *
-     * If time must be specified - use {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
-     *
-     * {@link https://www.w3.org/ns/activitystreams#deleted Docs}
-     */
-    deleted?: DeletedField;
+	/**
+	 * On a Tombstone object, the deleted property is a timestamp
+	 * for when the object was deleted.
+	 *
+	 * If time must be specified - use {@link https://www.w3schools.blog/xsd-date-and-time-data-types xsd:dateTime}
+	 *
+	 * {@link https://www.w3.org/ns/activitystreams#deleted Docs}
+	 */
+	deleted?: DeletedField;
 }
+
+export const ObjectIsTombstone = (object: APObject): object is APTombstone => {
+	return object.type == "Tombstone";
+};
diff --git a/src/model-interfaces/documents/audio.interface.ts b/src/model-interfaces/documents/audio.interface.ts
index 4032139..03bca19 100644
--- a/src/model-interfaces/documents/audio.interface.ts
+++ b/src/model-interfaces/documents/audio.interface.ts
@@ -1,3 +1,7 @@
-import { APDocument } from './document.interface';
+import { APObject } from "../common/object.interface";
 
-export type APAudio = APDocument
\ No newline at end of file
+export type APAudio = APObject & { type: "Audio" };
+
+export const ObjectIsAudio = (object: APObject): object is APAudio => {
+	return object.type == "Audio";
+};
diff --git a/src/model-interfaces/documents/document.interface.ts b/src/model-interfaces/documents/document.interface.ts
index 6195ef2..6ebfe34 100644
--- a/src/model-interfaces/documents/document.interface.ts
+++ b/src/model-interfaces/documents/document.interface.ts
@@ -1,3 +1,7 @@
-import {APObject} from '../common/object.interface';
+import { APObject } from "../common/object.interface";
 
-export type APDocument = APObject
+export type APDocument = APObject & { type: "Document" };
+
+export const ObjectIsDocument = (object: APObject): object is APDocument => {
+	return object.type == "Document";
+};
diff --git a/src/model-interfaces/documents/image.interface.ts b/src/model-interfaces/documents/image.interface.ts
index 536d175..ba9a6ae 100644
--- a/src/model-interfaces/documents/image.interface.ts
+++ b/src/model-interfaces/documents/image.interface.ts
@@ -1,3 +1,7 @@
-import { APDocument } from './document.interface';
+import { APObject } from "../common/object.interface";
 
-export type APImage = APDocument
\ No newline at end of file
+export type APImage = APObject & { type: "Image" };
+
+export const ObjectIsImage = (object: APObject): object is APImage => {
+	return object.type == "Image";
+};
diff --git a/src/model-interfaces/documents/page.interface.ts b/src/model-interfaces/documents/page.interface.ts
index a8fa6e5..cc23623 100644
--- a/src/model-interfaces/documents/page.interface.ts
+++ b/src/model-interfaces/documents/page.interface.ts
@@ -1,3 +1,7 @@
-import { APDocument } from './document.interface';
+import { APObject } from "../common/object.interface";
 
-export type APPage = APDocument
\ No newline at end of file
+export type APPage = APObject & { type: "Page" };
+
+export const ObjectIsPage = (object: APObject): object is APPage => {
+	return object.type == "Page";
+};
diff --git a/src/model-interfaces/documents/video.interface.ts b/src/model-interfaces/documents/video.interface.ts
index 205f7e1..fe9af52 100644
--- a/src/model-interfaces/documents/video.interface.ts
+++ b/src/model-interfaces/documents/video.interface.ts
@@ -1,3 +1,7 @@
-import { APDocument } from './document.interface';
+import { APObject } from "../common/object.interface";
 
-export type APVideo = APDocument
\ No newline at end of file
+export type APVideo = APObject & { type: "Video" };
+
+export const ObjectIsVideo = (object: APObject): object is APVideo => {
+	return object.type == "Video";
+};
diff --git a/src/model-interfaces/index.ts b/src/model-interfaces/index.ts
index 212e7cc..2cce63b 100644
--- a/src/model-interfaces/index.ts
+++ b/src/model-interfaces/index.ts
@@ -1,59 +1,59 @@
-export * from './common/article.interface';
-export * from './common/event.interface';
-export * from './common/link.interface';
-export * from './common/mention.interface';
-export * from './common/note.interface';
-export * from './common/object.interface';
-export * from './common/place.interface';
-export * from './common/profile.interface';
-export * from './common/tombstone.interface';
-export * from './common/relationship.interface';
+export * from "./common/article.interface";
+export * from "./common/event.interface";
+export * from "./common/link.interface";
+export * from "./common/mention.interface";
+export * from "./common/note.interface";
+export * from "./common/object.interface";
+export * from "./common/place.interface";
+export * from "./common/profile.interface";
+export * from "./common/tombstone.interface";
+export * from "./common/relationship.interface";
 
-export * from './activities/activity.interface';
-export * from './activities/intransitive-activity.interface';
-export * from './activities/question.interface';
-export * from './activities/accept.interface';
-export * from './activities/add.interface';
-export * from './activities/announce.interface';
-export * from './activities/arrive.interface';
-export * from './activities/block.interface';
-export * from './activities/create.interface';
-export * from './activities/delete.interface';
-export * from './activities/dislike.interface';
-export * from './activities/flag.interface';
-export * from './activities/follow.interface';
-export * from './activities/ignore.interface';
-export * from './activities/invite.interface';
-export * from './activities/join.interface';
-export * from './activities/leave.interface';
-export * from './activities/like.interface';
-export * from './activities/listen.interface';
-export * from './activities/move.interface';
-export * from './activities/offer.interface';
-export * from './activities/read.interface';
-export * from './activities/reject.interface';
-export * from './activities/remove.interface';
-export * from './activities/tentative-accept.interface';
-export * from './activities/tentative-reject.interface';
-export * from './activities/travel.interface';
-export * from './activities/undo.interface';
-export * from './activities/update.interface';
-export * from './activities/view.interface';
+export * from "./activities/activity.interface";
+export * from "./activities/intransitive-activity.interface";
+export * from "./activities/question.interface";
+export * from "./activities/accept.interface";
+export * from "./activities/add.interface";
+export * from "./activities/announce.interface";
+export * from "./activities/arrive.interface";
+export * from "./activities/block.interface";
+export * from "./activities/create.interface";
+export * from "./activities/delete.interface";
+export * from "./activities/dislike.interface";
+export * from "./activities/flag.interface";
+export * from "./activities/follow.interface";
+export * from "./activities/ignore.interface";
+export * from "./activities/invite.interface";
+export * from "./activities/join.interface";
+export * from "./activities/leave.interface";
+export * from "./activities/like.interface";
+export * from "./activities/listen.interface";
+export * from "./activities/move.interface";
+export * from "./activities/offer.interface";
+export * from "./activities/read.interface";
+export * from "./activities/reject.interface";
+export * from "./activities/remove.interface";
+export * from "./activities/tentative-accept.interface";
+export * from "./activities/tentative-reject.interface";
+export * from "./activities/travel.interface";
+export * from "./activities/undo.interface";
+export * from "./activities/update.interface";
+export * from "./activities/view.interface";
 
-export * from './actors/actor.interface';
-export * from './actors/application.interface';
-export * from './actors/organization.interface';
-export * from './actors/group.interface';
-export * from './actors/person.interface';
-export * from './actors/service.interface';
+export * from "./actors/actor.interface";
+export * from "./actors/application.interface";
+export * from "./actors/organization.interface";
+export * from "./actors/group.interface";
+export * from "./actors/person.interface";
+export * from "./actors/service.interface";
 
-export * from './collections/collection.interface';
-export * from './collections/collection-page.interface';
-export * from './collections/ordered-collection.interface';
-export * from './collections/ordered-collection-page.interface';
+export * from "./collections/collection.interface";
+export * from "./collections/collection-page.interface";
+export * from "./collections/ordered-collection.interface";
+export * from "./collections/ordered-collection-page.interface";
 
-export * from './documents/document.interface';
-export * from './documents/audio.interface';
-export * from './documents/image.interface';
-export * from './documents/page.interface';
-export * from './documents/video.interface';
\ No newline at end of file
+export * from "./documents/document.interface";
+export * from "./documents/audio.interface";
+export * from "./documents/image.interface";
+export * from "./documents/page.interface";
+export * from "./documents/video.interface";