diff --git a/GuessNN-webapp/src/App.vue b/GuessNN-webapp/src/App.vue
index e705f67..eaf192e 100644
--- a/GuessNN-webapp/src/App.vue
+++ b/GuessNN-webapp/src/App.vue
@@ -1,15 +1,81 @@
 <template>
-	<main-component></main-component>
+	<div class="container">
+		<loading-indicator :loaded="!isLoading" :error="hasErrors" :class="{'loading': isLoading}">
+			<main-component :entities="entities" :concepts="concepts" :target="targetEntity??''"></main-component>
+			<template #error-message>
+				<span>{{entitiesError}} {{conceptsError}}</span>
+			</template>
+		</loading-indicator>
+	</div>
 </template>
 
 <script lang="ts">
 import MainComponent from "./components/MainComponent.vue";
+import LoadingIndicator from "@/components/LoadingIndicator.vue";
+import { defineComponent } from "vue";
+import { fetchJSON } from "@/Utils";
+import type { NamedEntity } from "@/NamedEntity";
+import type { Concept } from "@/Concept";
 
-export default {
-	components: { MainComponent },
-};
+const entitiesURL = "/entities.json";
+const conceptsURL = "/concepts.json";
+
+export default defineComponent({
+	components: { LoadingIndicator, MainComponent },
+	data() {
+		return {
+			entitiesLoading: true,
+			entitiesError: "",
+			entities: [] as Array<NamedEntity>,
+			conceptsLoading: true,
+			conceptsError: "",
+			concepts: [] as Array<Concept>,
+			targetEntity: null as string | null,
+		};
+	},
+	computed: {
+		isLoading(): boolean {
+			return this.entitiesLoading || this.conceptsLoading;
+		},
+		hasErrors(): boolean {
+			return this.entitiesError.length > 0 || this.conceptsError.length > 0;
+		},
+	},
+	mounted() {
+		this.entitiesLoading = true;
+		this.entitiesError = "";
+		this.entities = [];
+		fetchJSON(entitiesURL)
+			.then(json => this.entities = json as Array<NamedEntity>) //TODO: Create NamedEntity.fromJSON
+			.catch((err:Error) => this.entitiesError = `Error fetching entities: ${err.message}`)
+			.finally(() => this.entitiesLoading = false);
+
+		this.conceptsLoading = true;
+		this.conceptsError = "";
+		this.concepts = [];
+		this.targetEntity = null;
+		fetchJSON(conceptsURL)
+			.then(json => {
+				// TODO: Create Concept.fromJSON
+				this.concepts = (json as any).concepts as Array<Concept>; // eslint-disable-line @typescript-eslint/no-explicit-any
+				// TODO: verify presence of target in json
+				this.targetEntity = (json as any).target as string;  // eslint-disable-line @typescript-eslint/no-explicit-any
+			})
+			.catch((err:Error) => this.conceptsError = `Error fetching concepts: ${err.message}`)
+			.finally(() => this.conceptsLoading = false);
+	},
+});
 </script>
 
 <style lang="scss">
 @import "bootstrap/scss/bootstrap";
+@import "bootstrap-icons/font/bootstrap-icons";
+</style>
+
+<style scoped lang="scss">
+@import "bootstrap/scss/bootstrap";
+.loading {
+	@extend .position-absolute, .top-50, .start-50, .translate-middle;
+}
+
 </style>
diff --git a/GuessNN-webapp/src/components/LoadingIndicator.vue b/GuessNN-webapp/src/components/LoadingIndicator.vue
new file mode 100644
index 0000000..f5b514b
--- /dev/null
+++ b/GuessNN-webapp/src/components/LoadingIndicator.vue
@@ -0,0 +1,54 @@
+<template>
+	<slot v-if="error" name="error">
+		<div class="error">
+			<i class="bi bi-exclamation-triangle-fill"></i>
+			<slot name="error-message">
+				There was en error during loading.
+			</slot>
+		</div>
+	</slot>
+	<div v-else>
+		<slot v-if="loaded" name="default"></slot>
+		<div v-else class="loading-indicator">
+			<span>Loading...</span>
+		</div>
+	</div>
+</template>
+
+<script lang="ts">
+import { defineComponent } from "vue";
+
+export default defineComponent({
+	name: "LoadingIndicator",
+	props: {
+		loaded: {
+			type: Boolean,
+			default: false,
+		},
+		error: {
+			type: Boolean,
+			default: false,
+		},
+	},
+});
+</script>
+
+<style scoped lang="scss">
+@import "bootstrap/scss/bootstrap";
+
+.error {
+	@extend .alert, .alert-danger, .d-flex, .align-items-center;
+	i {
+		@extend .me-2;
+	}
+}
+
+.loading-indicator {
+	@extend .spinner-grow, .text-primary;
+
+	span {
+		@extend .visually-hidden;
+	}
+}
+
+</style>
diff --git a/GuessNN-webapp/src/components/MainComponent.vue b/GuessNN-webapp/src/components/MainComponent.vue
index 5e532da..b5e0ab1 100644
--- a/GuessNN-webapp/src/components/MainComponent.vue
+++ b/GuessNN-webapp/src/components/MainComponent.vue
@@ -1,37 +1,44 @@
 <template>
-	<div v-if="fetchErrors" class="error">
-		<div v-for="err in fetchErrors" :key="err">
-			{{ err }}<br />
-		</div>
-	</div>
-
 	<form v-if="entities.length > 0" @submit.prevent="submitGuess">
 		Enter a guess: <input type="text" v-model="guessFieldValue" /> <br />
 		<div v-if="guessError" class="error">{{ guessError }} <br /></div>
 		<span class="possibleTypes">It can be any {{ [...entityTypes].join(", ") }}.</span>
 	</form>
+	<div v-else>
+		Error: component instantiated but entities are empty.
+	</div>
 
 </template>
 
 <script lang="ts">
-import { defineComponent } from "vue";
+import { defineComponent, type PropType } from "vue";
 import type { NamedEntity } from "@/NamedEntity";
 import type { Concept } from "@/Concept";
-import { fetchJSON } from "@/Utils";
 
-const entitiesURL = "/entities.json";
-const conceptsURL = "/concepts.json";
 
 export default defineComponent({
 	name: "MainComponent",
+	props: {
+		entities: {
+			type: Object as PropType<Array<NamedEntity>>,
+			required: true,
+			validator: (value: Array<NamedEntity>) => value.length > 0,
+		},
+		concepts: {
+			type: Object as PropType<Array<Concept>>,
+			required: true,
+			validator: (value: Array<Concept>) => value.length > 0,
+		},
+		target: {
+			type: String,
+			required: true,
+			validator: (value: string) => value.length > 0,
+		},
+	},
 	data() {
 		return {
 			guessFieldValue: "",
-			fetchErrors: [] as Array<string>,
 			guessError: null as string | null,
-			entities: [] as Array<NamedEntity>,
-			concepts: [] as Array<Concept>,
-			target: null as string | null,
 		};
 	},
 	computed: {
@@ -58,17 +65,6 @@ export default defineComponent({
 			return result;
 		},
 	},
-	created() {
-		this.fetchErrors = [];
-		fetchJSON(entitiesURL)
-			.then(json => this.entities = json as Array<NamedEntity>)
-			.catch(this.fetchErrors.push);
-		fetchJSON(conceptsURL)
-			.then(json => {
-				this.concepts = (json as any).concepts as Array<Concept>; // eslint-disable-line @typescript-eslint/no-explicit-any
-				this.target = (json as any).target as string;  // eslint-disable-line @typescript-eslint/no-explicit-any
-			});
-	},
 	methods: {
 		submitGuess() {
 			this.guessError = null;
diff --git a/GuessNN-webapp/tsconfig.json b/GuessNN-webapp/tsconfig.json
index 3463d8d..1c26083 100644
--- a/GuessNN-webapp/tsconfig.json
+++ b/GuessNN-webapp/tsconfig.json
@@ -12,6 +12,7 @@
 		"./src/*"
 	  ]
 	},
+	"lib": ["es2018"],
 	"noImplicitThis": true,
   },
   "references": [