diff --git a/backend/src/data/themes.ts b/backend/src/data/themes.ts
index b0fc930c..edbdb113 100644
--- a/backend/src/data/themes.ts
+++ b/backend/src/data/themes.ts
@@ -1,7 +1,4 @@
-export interface Theme {
-    title: string;
-    hruids: string[];
-}
+import {Theme} from "dwengo-1-common/src/interfaces/theme";
 
 export const themes: Theme[] = [
     {
diff --git a/common/src/interfaces/theme.d.ts b/common/src/interfaces/theme.d.ts
new file mode 100644
index 00000000..5334b775
--- /dev/null
+++ b/common/src/interfaces/theme.d.ts
@@ -0,0 +1,4 @@
+export interface Theme {
+    title: string;
+    hruids: string[];
+}
diff --git a/frontend/src/controllers/themes.ts b/frontend/src/controllers/themes.ts
index d6c8be98..7804f2b7 100644
--- a/frontend/src/controllers/themes.ts
+++ b/frontend/src/controllers/themes.ts
@@ -1,11 +1,12 @@
 import { BaseController } from "@/controllers/base-controller.ts";
+import type {Theme} from "dwengo-1-common/src/interfaces/theme";
 
 export class ThemeController extends BaseController {
     constructor() {
         super("theme");
     }
 
-    async getAll(language: string | null = null): Promise<unknown> {
+    async getAll(language: string | null = null): Promise<Theme[]> {
         const query = language ? { language } : undefined;
         return this.get("/", query);
     }
diff --git a/frontend/src/queries/teachers.ts b/frontend/src/queries/teachers.ts
index 3ab1f39b..3bd625b1 100644
--- a/frontend/src/queries/teachers.ts
+++ b/frontend/src/queries/teachers.ts
@@ -43,7 +43,7 @@ export function useTeachersQuery(
 ): UseQueryReturnType<TeachersResponse, Error> {
     return useQuery({
         queryKey: computed(() => TEACHERS_QUERY_KEY(toValue(full))),
-        queryFn: () => teacherController.getAll(toValue(full)),
+        queryFn: async () => teacherController.getAll(toValue(full)),
     });
 }
 
@@ -52,7 +52,7 @@ export function useTeacherQuery(
 ): UseQueryReturnType<TeacherResponse, Error> {
     return useQuery({
         queryKey: computed(() => TEACHER_QUERY_KEY(toValue(username)!)),
-        queryFn: () => teacherController.getByUsername(toValue(username)!),
+        queryFn: async () => teacherController.getByUsername(toValue(username)!),
         enabled: () => Boolean(toValue(username)),
     });
 }
@@ -63,7 +63,7 @@ export function useTeacherClassesQuery(
 ): UseQueryReturnType<ClassesResponse, Error> {
     return useQuery({
         queryKey: computed(() => TEACHER_CLASSES_QUERY_KEY(toValue(username)!, toValue(full))),
-        queryFn: () => teacherController.getClasses(toValue(username)!, toValue(full)),
+        queryFn: async () => teacherController.getClasses(toValue(username)!, toValue(full)),
         enabled: () => Boolean(toValue(username)),
     });
 }
@@ -74,7 +74,7 @@ export function useTeacherStudentsQuery(
 ): UseQueryReturnType<StudentsResponse, Error> {
     return useQuery({
         queryKey: computed(() => TEACHER_STUDENTS_QUERY_KEY(toValue(username)!, toValue(full))),
-        queryFn: () => teacherController.getStudents(toValue(username)!, toValue(full)),
+        queryFn: async () => teacherController.getStudents(toValue(username)!, toValue(full)),
         enabled: () => Boolean(toValue(username)),
     });
 }
@@ -85,7 +85,7 @@ export function useTeacherQuestionsQuery(
 ): UseQueryReturnType<QuestionsResponse, Error> {
     return useQuery({
         queryKey: computed(() => TEACHER_QUESTIONS_QUERY_KEY(toValue(username)!, toValue(full))),
-        queryFn: () => teacherController.getQuestions(toValue(username)!, toValue(full)),
+        queryFn: async () => teacherController.getQuestions(toValue(username)!, toValue(full)),
         enabled: () => Boolean(toValue(username)),
     });
 }
@@ -96,7 +96,7 @@ export function useTeacherJoinRequestsQuery(
 ): UseQueryReturnType<JoinRequestsResponse, Error> {
     return useQuery({
         queryKey: computed(() => JOIN_REQUESTS_QUERY_KEY(toValue(username)!, toValue(classId)!)),
-        queryFn: () => teacherController.getStudentJoinRequests(toValue(username)!, toValue(classId)!),
+        queryFn: async () => teacherController.getStudentJoinRequests(toValue(username)!, toValue(classId)!),
         enabled: () => Boolean(toValue(username)) && Boolean(toValue(classId)),
     });
 }
@@ -110,7 +110,7 @@ export function useCreateTeacherMutation(): UseMutationReturnType<
     const queryClient = useQueryClient();
 
     return useMutation({
-        mutationFn: (data: TeacherDTO) => teacherController.createTeacher(data),
+        mutationFn: async (data: TeacherDTO) => teacherController.createTeacher(data),
         onSuccess: async () => {
             await queryClient.invalidateQueries({ queryKey: ["teachers"] });
         },
@@ -126,7 +126,7 @@ export function useDeleteTeacherMutation(): UseMutationReturnType<
     const queryClient = useQueryClient();
 
     return useMutation({
-        mutationFn: (username: string) => teacherController.deleteTeacher(username),
+        mutationFn: async (username: string) => teacherController.deleteTeacher(username),
         onSuccess: async (deletedTeacher) => {
             await queryClient.invalidateQueries({ queryKey: ["teachers"] });
             await queryClient.invalidateQueries({ queryKey: TEACHER_QUERY_KEY(deletedTeacher.teacher.username) });
@@ -143,7 +143,7 @@ export function useUpdateJoinRequestMutation(): UseMutationReturnType<
     const queryClient = useQueryClient();
 
     return useMutation({
-        mutationFn: ({ teacherUsername, classId, studentUsername, accepted }) =>
+        mutationFn: async ({ teacherUsername, classId, studentUsername, accepted }) =>
             teacherController.updateStudentJoinRequest(teacherUsername, classId, studentUsername, accepted),
         onSuccess: async (deletedJoinRequest) => {
             const username = deletedJoinRequest.request.requester;
diff --git a/frontend/src/queries/themes.ts b/frontend/src/queries/themes.ts
index 65bf9237..dcd251e7 100644
--- a/frontend/src/queries/themes.ts
+++ b/frontend/src/queries/themes.ts
@@ -1,10 +1,11 @@
-import { useQuery } from "@tanstack/vue-query";
+import {useQuery, type UseQueryReturnType} from "@tanstack/vue-query";
 import { type MaybeRefOrGetter, toValue } from "vue";
 import { ThemeController } from "@/controllers/themes.ts";
+import type {Theme} from "dwengo-1-common/src/interfaces/theme";
 
 const themeController = new ThemeController();
 
-export function useThemeQuery(language: MaybeRefOrGetter<string | undefined>) {
+export function useThemeQuery(language: MaybeRefOrGetter<string | undefined>): UseQueryReturnType<Theme[], Error> {
     return useQuery({
         queryKey: ["themes", language],
         queryFn: async () => {
@@ -15,7 +16,7 @@ export function useThemeQuery(language: MaybeRefOrGetter<string | undefined>) {
     });
 }
 
-export function useThemeHruidsQuery(themeKey: MaybeRefOrGetter<string | undefined>) {
+export function useThemeHruidsQuery(themeKey: MaybeRefOrGetter<string | undefined>): UseQueryReturnType<string[], Error> {
     return useQuery({
         queryKey: ["theme-hruids", themeKey],
         queryFn: async () => themeController.getHruidsByKey(toValue(themeKey)!),