diff --git a/frontend/src/components/MenuBar.vue b/frontend/src/components/MenuBar.vue
index f942babc..95468351 100644
--- a/frontend/src/components/MenuBar.vue
+++ b/frontend/src/components/MenuBar.vue
@@ -29,11 +29,11 @@
     ]);
 
     // Logic to change the language of the website to the selected language
-    const changeLanguage = (langCode: string) => {
+    function changeLanguage(langCode: string): void {
         locale.value = langCode;
         localStorage.setItem("user-lang", langCode);
         console.log(langCode);
-    };
+    }
 </script>
 
 <template>
diff --git a/frontend/src/router/index.ts b/frontend/src/router/index.ts
index 5f2c4624..7ad5763d 100644
--- a/frontend/src/router/index.ts
+++ b/frontend/src/router/index.ts
@@ -20,13 +20,13 @@ const router = createRouter({
         {
             path: "/",
             name: "home",
-            component: () => import("../views/HomePage.vue"),
+            component: async (): Promise<unknown> => import("../views/HomePage.vue"),
             meta: { requiresAuth: false },
         },
         {
             path: "/login",
             name: "LoginPage",
-            component: () => import("../views/LoginPage.vue"),
+            component: async (): Promise<unknown> => import("../views/LoginPage.vue"),
             meta: { requiresAuth: false },
         },
         {
@@ -108,7 +108,7 @@ const router = createRouter({
     ],
 });
 
-router.beforeEach(async (to, from, next) => {
+router.beforeEach(async (to, _from, next) => {
     // Verify if user is logged in before accessing certain routes
     if (to.meta.requiresAuth) {
         if (!authState.isLoggedIn.value) {
diff --git a/frontend/src/services/auth/auth-config-loader.ts b/frontend/src/services/auth/auth-config-loader.ts
index ce8a33ca..05e2f537 100644
--- a/frontend/src/services/auth/auth-config-loader.ts
+++ b/frontend/src/services/auth/auth-config-loader.ts
@@ -1,10 +1,11 @@
 import apiClient from "@/services/api-client.ts";
 import type { FrontendAuthConfig } from "@/services/auth/auth.d.ts";
+import type {UserManagerSettings} from "oidc-client-ts";
 
 /**
  * Fetch the authentication configuration from the backend.
  */
-export async function loadAuthConfig() {
+export async function loadAuthConfig(): Promise<Record<string, UserManagerSettings>> {
     const authConfig = (await apiClient.get<FrontendAuthConfig>("auth/config")).data;
     return {
         student: {
diff --git a/frontend/src/services/auth/auth-service.ts b/frontend/src/services/auth/auth-service.ts
index 2b3d2807..60765a5a 100644
--- a/frontend/src/services/auth/auth-service.ts
+++ b/frontend/src/services/auth/auth-service.ts
@@ -49,7 +49,7 @@ const isLoggedIn = computed(() => authState.user !== null);
 /**
  * Redirect the user to the login page where he/she can choose whether to log in as a student or teacher.
  */
-async function initiateLogin() {
+async function initiateLogin(): Promise<void> {
     await router.push(loginRoute);
 }
 
@@ -77,12 +77,12 @@ async function handleLoginCallback(): Promise<void> {
 /**
  * Refresh an expired authorization token.
  */
-async function renewToken() {
+async function renewToken(): Promise<User | null> {
     const activeRole = authStorage.getActiveRole();
     if (!activeRole) {
         console.log("Can't renew the token: Not logged in!");
         await initiateLogin();
-        return;
+        return null;
     }
     try {
         return await (await getUserManagers())[activeRole].signinSilent();
@@ -91,6 +91,7 @@ async function renewToken() {
         console.log(error);
         await initiateLogin();
     }
+    return null;
 }
 
 /**
@@ -113,7 +114,7 @@ apiClient.interceptors.request.use(
         }
         return reqConfig;
     },
-    (error) => Promise.reject(error),
+    async (error) => Promise.reject(error),
 );
 
 // Registering interceptor to refresh the token when a request failed because it was expired.
@@ -121,7 +122,7 @@ apiClient.interceptors.response.use(
     (response) => response,
     async (error: AxiosError<{ message?: string }>) => {
         if (error.response?.status === 401) {
-            if (error.response!.data.message === "token_expired") {
+            if (error.response.data.message === "token_expired") {
                 console.log("Access token expired, trying to refresh...");
                 await renewToken();
                 return apiClient(error.config!); // Retry the request
diff --git a/frontend/src/services/auth/auth-storage.ts b/frontend/src/services/auth/auth-storage.ts
index 0f5eb43d..ea7266a5 100644
--- a/frontend/src/services/auth/auth-storage.ts
+++ b/frontend/src/services/auth/auth-storage.ts
@@ -12,7 +12,7 @@ export default {
      * Set the role the user is currently logged in as from the local persistent storage.
      * This should happen when the user logs in with another account.
      */
-    setActiveRole(role: Role) {
+    setActiveRole(role: Role): void {
         localStorage.setItem("activeRole", role);
     },
 
@@ -20,7 +20,7 @@ export default {
      * Remove the saved current role from the local persistent storage.
      * This should happen when the user is logged out.
      */
-    deleteActiveRole() {
+    deleteActiveRole(): void {
         localStorage.removeItem("activeRole");
     },
 };
diff --git a/frontend/src/services/auth/auth.d.ts b/frontend/src/services/auth/auth.d.ts
index 8b01e408..d8c5990f 100644
--- a/frontend/src/services/auth/auth.d.ts
+++ b/frontend/src/services/auth/auth.d.ts
@@ -1,22 +1,22 @@
 import { type User, UserManager } from "oidc-client-ts";
 
-export type AuthState = {
+export interface AuthState {
     user: User | null;
     accessToken: string | null;
     activeRole: Role | null;
-};
+}
 
-export type FrontendAuthConfig = {
+export interface FrontendAuthConfig {
     student: FrontendIdpConfig;
     teacher: FrontendIdpConfig;
-};
+}
 
-export type FrontendIdpConfig = {
+export interface FrontendIdpConfig {
     authority: string;
     clientId: string;
     scope: string;
     responseType: string;
-};
+}
 
 export type Role = "student" | "teacher";
-export type UserManagersForRoles = { student: UserManager; teacher: UserManager };
+export interface UserManagersForRoles { student: UserManager; teacher: UserManager }
diff --git a/frontend/src/views/HomePage.vue b/frontend/src/views/HomePage.vue
index e9d53770..b358a150 100644
--- a/frontend/src/views/HomePage.vue
+++ b/frontend/src/views/HomePage.vue
@@ -5,7 +5,7 @@
 
     const testResponse = ref(null);
 
-    async function testAuthenticated() {
+    async function testAuthenticated(): Promise<void> {
         testResponse.value = await apiClient.get("/auth/testAuthenticatedOnly");
     }
 </script>
diff --git a/frontend/src/views/LoginPage.vue b/frontend/src/views/LoginPage.vue
index a538a80c..d430d7d8 100644
--- a/frontend/src/views/LoginPage.vue
+++ b/frontend/src/views/LoginPage.vue
@@ -2,15 +2,15 @@
     import dwengoLogo from "../../../assets/img/dwengo-groen-zwart.svg";
     import auth from "@/services/auth/auth-service.ts";
 
-    function loginAsStudent() {
+    function loginAsStudent(): void {
         auth.loginAs("student");
     }
 
-    function loginAsTeacher() {
+    function loginAsTeacher(): void {
         auth.loginAs("teacher");
     }
 
-    function performLogout() {
+    function performLogout(): void {
         auth.logout();
     }
 </script>
diff --git a/frontend/vite.config.ts b/frontend/vite.config.ts
index 9ebf424b..15cf34b3 100644
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -2,7 +2,6 @@ import { fileURLToPath, URL } from "node:url";
 
 import { defineConfig } from "vite";
 import vue from "@vitejs/plugin-vue";
-import vueDevTools from "vite-plugin-vue-devtools";
 
 // https://vite.dev/config/
 export default defineConfig({