diff --git a/src/fullcalendar/eventSources/eventSource.js b/src/fullcalendar/eventSources/eventSource.js
index 6f73327704..98e9833662 100644
--- a/src/fullcalendar/eventSources/eventSource.js
+++ b/src/fullcalendar/eventSources/eventSource.js
@@ -12,7 +12,7 @@ import { eventSourceFunction } from './eventSourceFunction.js'
 /**
  * Returns a function to generate a FullCalendar event-source based on the Vuex calendar model
  *
- * @return {function(*=): {backgroundColor: *, borderColor: *, className: *, id: *, textColor: *, events: events}}
+ * @return {(calendar: object) => {id: string, backgroundColor: string, borderColor: string, editable?: boolean, events: (info: {start: Date, end: Date, timeZone: string}, successCallback: (events: object[]) => void, failureCallback: (error: Error) => void) => Promise<void>}}
  */
 export default function() {
 	const fetchedTimeRangesStore = useFetchedTimeRangesStore()
diff --git a/src/fullcalendar/interaction/eventClick.js b/src/fullcalendar/interaction/eventClick.js
index c2e1cb4f25..1b25d7eebf 100644
--- a/src/fullcalendar/interaction/eventClick.js
+++ b/src/fullcalendar/interaction/eventClick.js
@@ -23,7 +23,7 @@ import { errorCatchAsync } from '../utils/errors.js'
  * @param {Window} window The window object
  * @param {boolean} isWidget Whether the calendar is embedded in a widget
  * @param {object} ref The ref object of CalendarGrid component
- * @return {Function}
+ * @return {(info: {event: EventDef}) => Promise<void>}
  */
 export default function(router, route, window, isWidget = false, ref = undefined) {
 	const widgetStore = useWidgetStore()
diff --git a/src/fullcalendar/interaction/eventDrop.js b/src/fullcalendar/interaction/eventDrop.js
index 5b059f4b82..f46c14b6c2 100644
--- a/src/fullcalendar/interaction/eventDrop.js
+++ b/src/fullcalendar/interaction/eventDrop.js
@@ -18,7 +18,7 @@ import { errorCatchAsync } from '../utils/errors.js'
  * Returns a function to drop an event at a different position
  *
  * @param {object} fcAPI The fullcalendar api
- * @return {Function}
+ * @return {(info: {event: EventDef, delta: object, revert: () => void}) => Promise<void>}
  */
 export default function(fcAPI) {
 	const calendarsStore = useCalendarsStore()
diff --git a/src/fullcalendar/interaction/eventResize.js b/src/fullcalendar/interaction/eventResize.js
index 739479029a..9b209447a7 100644
--- a/src/fullcalendar/interaction/eventResize.js
+++ b/src/fullcalendar/interaction/eventResize.js
@@ -12,7 +12,7 @@ import logger from '@/utils/logger.js'
 /**
  * Returns a function to resize an event
  *
- * @return {Function}
+ * @return {(info: {event: EventDef, startDelta: object, endDelta: object, revert: () => void}) => Promise<void>}
  */
 export default function() {
 	const calendarsStore = useCalendarsStore()
diff --git a/src/fullcalendar/interaction/select.js b/src/fullcalendar/interaction/select.js
index 1d3666afde..298e21b78c 100644
--- a/src/fullcalendar/interaction/select.js
+++ b/src/fullcalendar/interaction/select.js
@@ -14,7 +14,7 @@ import { errorCatch } from '../utils/errors.js'
  * @param {object} router The Vue router
  * @param {object} route The Vue route
  * @param {Window} window The window object
- * @return {Function}
+ * @return {(info: {start: Date, end: Date, allDay: boolean}) => void}
  */
 export default function(router, route, window) {
 	const settingsStore = useSettingsStore()
diff --git a/src/fullcalendar/utils/errors.js b/src/fullcalendar/utils/errors.js
index f8294167d0..b2d9171d20 100644
--- a/src/fullcalendar/utils/errors.js
+++ b/src/fullcalendar/utils/errors.js
@@ -8,10 +8,11 @@ import logger from '@/utils/logger.js'
 /**
  * Wraps a FullCalendar hook function with error logging
  *
- * @param {Function} hookFn The hook function to wrap
+ * @template {(...args: unknown[]) => unknown} T
+ * @param {T} hookFn The hook function to wrap
  * @param {string} hookName The name of the hook for logging
- * @param {*} [defaultReturn] The default return value if the hook throws an error
- * @return {Function} The wrapped hook function
+ * @param {ReturnType<T>} [defaultReturn] The default return value if the hook throws an error
+ * @return {T} The wrapped hook function
  */
 export function errorCatch(hookFn, hookName, defaultReturn = undefined) {
 	return function(...args) {
@@ -27,9 +28,10 @@ export function errorCatch(hookFn, hookName, defaultReturn = undefined) {
 /**
  * Wraps an async FullCalendar hook function with error logging
  *
- * @param {Function} hookFn The async hook function to wrap
+ * @template {(...args: unknown[]) => unknown} T
+ * @param {T} hookFn The async hook function to wrap
  * @param {string} hookName The name of the hook for logging
- * @return {Function} The wrapped async hook function
+ * @return {(...args: Parameters<T>) => Promise<Awaited<ReturnType<T>>|undefined>} The wrapped async hook function
  */
 export function errorCatchAsync(hookFn, hookName) {
 	return async function(...args) {
diff --git a/src/mixins/EditorMixin.js b/src/mixins/EditorMixin.js
index 71e4eb68ef..1b1a4c9615 100644
--- a/src/mixins/EditorMixin.js
+++ b/src/mixins/EditorMixin.js
@@ -156,7 +156,7 @@ export default {
 		 * Returns the color of the calendar selected by the user
 		 * This is used to color illustration
 		 *
-		 * @return {string|*}
+		 * @return {string}
 		 */
 		selectedCalendarColor() {
 			if (!this.selectedCalendar) {
@@ -939,7 +939,7 @@ export default {
 	 *
 	 * @param {object} to The route to navigate to
 	 * @param {object} from The route coming from
-	 * @param {Function} next Function to be called when ready to load the next view
+	 * @param {(vm?: object) => void} next Function to be called when ready to load the next view
 	 */
 	async beforeRouteEnter(to, from, next) {
 		if (to.name === 'NewFullView' || to.name === 'NewPopoverView') {
@@ -1014,7 +1014,7 @@ export default {
 	 *
 	 * @param {object} to The route to navigate to
 	 * @param {object} from The route coming from
-	 * @param {Function} next Function to be called when ready to load the next view
+	 * @param {(vm?: object) => void} next Function to be called when ready to load the next view
 	 */
 	async beforeRouteUpdate(to, from, next) {
 		// If we are in the New Event dialog, we want to update the selected time
@@ -1092,7 +1092,7 @@ export default {
 	 *
 	 * @param {object} to The route to navigate to
 	 * @param {object} from The route coming from
-	 * @param {Function} next Function to be called when ready to load the next view
+	 * @param {(vm?: object) => void} next Function to be called when ready to load the next view
 	 */
 	async beforeRouteLeave(to, from, next) {
 		// requiresActionOnRouteLeave is false when an action like deleting / saving / cancelling was already taken.
diff --git a/src/models/principal.js b/src/models/principal.js
index e9e053c467..dda4bdeb86 100644
--- a/src/models/principal.js
+++ b/src/models/principal.js
@@ -16,7 +16,7 @@ import { mapDavToRoomPrincipalProperties } from '@/models/principal/principal'
  * Creates a complete principal-object based on given props
  *
  * @param {object} props Principal-props already provided
- * @return {any}
+ * @return {object}
  */
 function getDefaultPrincipalObject(props) {
 	return { // Id of the principal
diff --git a/src/models/rfcProps.js b/src/models/rfcProps.js
index f6635d051d..51758400dc 100644
--- a/src/models/rfcProps.js
+++ b/src/models/rfcProps.js
@@ -8,7 +8,15 @@ import { getDefaultCategories } from '../defaults/defaultCategories.js'
 /**
  * Gets all supported RFC properties
  *
- * @return {{color: {readableName: *, icon: string, multiple: boolean, info: *}, timeTransparency: {readableName: *, defaultValue: string, icon: string, multiple: boolean, options: *[], info: *}, description: {readableName: *, icon: string, placeholder: *, defaultNumberOfRows: number}, location: {readableName: *, icon: string, placeholder: *}, categories: {readableName: *, icon: string, multiple: boolean, options: *, tagPlaceholder: *, placeholder: *, info: *}, accessClass: {readableName: *, defaultValue: string, icon: string, options: *[], multiple: boolean, info: *}, status: {readableName: *, defaultValue: string, icon: string, options: *[], multiple: boolean, info: *}}}
+ * @return {{
+ *   accessClass: {readableName: string, icon: string, options: {value: string, label: string}[], multiple: boolean, info: string, defaultValue: string},
+ *   location: {readableName: string, placeholder: string, icon: string},
+ *   description: {readableName: string, placeholder: string, icon: string, defaultNumberOfRows: number},
+ *   status: {readableName: string, icon: string, options: {value: string, label: string}[], multiple: boolean, info: string, defaultValue: string},
+ *   timeTransparency: {readableName: string, icon: string, multiple: boolean, info: string, options: {value: string, label: string}[], defaultValue: string},
+ *   categories: {readableName: string, icon: string, multiple: boolean, info: string, placeholder: string, tagPlaceholder: string, options: {value: string, label: string}[]},
+ *   color: {readableName: string, icon: string, multiple: boolean, info: string},
+ * }}
  */
 function getRFCProperties() {
 	return {
diff --git a/src/models/schedulingObject.js b/src/models/schedulingObject.js
index 18ae380373..5ae16afe47 100644
--- a/src/models/schedulingObject.js
+++ b/src/models/schedulingObject.js
@@ -152,7 +152,7 @@ function mapCalendarJsToSchedulingObject(calendarComponent) {
  * Extracts the first object from the calendar-component
  *
  * @param {CalendarComponent} calendarComponent The calendar-component
- * @return {any} First VEvent / VJournal / VTodo / VFreeBusy
+ * @return {object|undefined} First VEvent / VJournal / VTodo / VFreeBusy
  */
 function getFirstObjectFromCalendarComponent(calendarComponent) {
 	const vObjectIterator = calendarComponent.getVObjectIterator()
diff --git a/src/services/attachmentService.js b/src/services/attachmentService.js
index 3e81c89a7e..8391c2cd97 100644
--- a/src/services/attachmentService.js
+++ b/src/services/attachmentService.js
@@ -43,7 +43,7 @@ async function shareFile(path) {
  * @param {string} path The file path from the user's root directory. e.g. `/myfile.txt`
  * @param {string} sharedWith The user id to share the file with
  * @param {number} permissions The share permissions bitmask
- * @return {Promise<[{path: string, permissions, scope: string, name: string, backend: string, type: string},{path: string, permissions: *, scope: string, name: string, backend: string, type: string}]>}
+ * @return {Promise<{path: string, permissions: number, scope: string, name: string, backend: string, type: string}>}
  */
 async function shareFileWith(path, sharedWith, permissions = 17) {
 	try {
diff --git a/src/utils/alarms.js b/src/utils/alarms.js
index 5e7e0fbadc..8c4bfbb102 100644
--- a/src/utils/alarms.js
+++ b/src/utils/alarms.js
@@ -105,7 +105,7 @@ export function getTotalSecondsFromAmountAndUnitForTimedEvents(amount, unit, isB
  * Gets the amount of days / weeks, unit, hours and minutes from total seconds
  *
  * @param {number} totalSeconds Total amount of seconds
- * @return {{amount: *, unit: *, hours: *, minutes: *}}
+ * @return {{amount: number, unit: string, hours: number, minutes: number}}
  */
 export function getAmountHoursMinutesAndUnitForAllDayEvents(totalSeconds) {
 	const dayFactor = getFactorForAlarmUnit('days')
diff --git a/src/utils/color.js b/src/utils/color.js
index ec11991a88..976c0618e8 100644
--- a/src/utils/color.js
+++ b/src/utils/color.js
@@ -73,7 +73,7 @@ export function uidToHexColor(uid) {
  * Detects a color from a given string
  *
  * @param {string} color The color to get the real RGB hex string from
- * @return {string|boolean|*} String if color detected, boolean if not
+ * @return {string|boolean} String if color detected, boolean if not
  */
 export function detectColor(color) {
 	if (/^(#)((?:[A-Fa-f0-9]{3}){1,2})$/.test(color)) { // #ff00ff and #f0f