diff --git a/client/src/components/app_bar.tsx b/client/src/components/app_bar.tsx
index dffdc81..2c65a81 100644
--- a/client/src/components/app_bar.tsx
+++ b/client/src/components/app_bar.tsx
@@ -1,3 +1,6 @@
+/**
+ *  @file contains the navigation bars of the app.
+ */
 import * as React from 'react'
 import { FontAwesomeIcon } from '@fortawesome/react-fontawesome'
 import { faDownload, faUpload, faEraser, faBook, faBookOpen, faGlobe, faHome,
@@ -11,7 +14,7 @@ import { useAppDispatch, useAppSelector } from '../hooks'
 import { Button } from './button'
 import { downloadProgress } from './popup/erase'
 
-/** navigation buttons to switch between welcome-pages on mobile */
+/** navigation buttons for mobile welcome page to switch between intro/tree/inventory. */
 function MobileNavButtons({pageNumber, setPageNumber}:
   { pageNumber: number,
     setPageNumber: any}) {
@@ -49,61 +52,16 @@ function MobileNavButtons({pageNumber, setPageNumber}:
   </>
 }
 
+/** button to toggle dropdown menu. */
 function MenuButton({navOpen, setNavOpen}) {
   return <Button to="" className="btn toggle-width" id="menu-btn" onClick={(ev) => {setNavOpen(!navOpen)}}>
     {navOpen ? <FontAwesomeIcon icon={faXmark} /> : <FontAwesomeIcon icon={faBars} />}
   </Button>
 }
 
-/** the navigation bar on the welcome page */
-export function WelcomeAppBar({pageNumber, setPageNumber, gameInfo, toggleImpressum, toggleEraseMenu, toggleUploadMenu, toggleInfo} : {
-  pageNumber: number,
-  setPageNumber: any,
-  gameInfo: GameInfo,
-  toggleImpressum: any,
-  toggleEraseMenu: any,
-  toggleUploadMenu: any,
-  toggleInfo: any
-}) {
-  const gameId = React.useContext(GameIdContext)
-  const gameProgress = useAppSelector(selectProgress(gameId))
-  const {mobile} = React.useContext(MobileContext)
-  const [navOpen, setNavOpen] = React.useState(false)
-
-  return <div className="app-bar">
-    <div>
-      <Button inverted="false" title="back to games selection" to="/">
-        <FontAwesomeIcon icon={faArrowLeft} />&nbsp;<FontAwesomeIcon icon={faGlobe} />
-      </Button>
-      <span className="app-bar-title"></span>
-    </div>
-    <div>
-      {!mobile && <span className="app-bar-title">{gameInfo?.title}</span>}
-    </div>
-    <div className="nav-btns">
-      {mobile && <MobileNavButtons pageNumber={pageNumber} setPageNumber={setPageNumber} />}
-      <MenuButton navOpen={navOpen} setNavOpen={setNavOpen} />
-    </div>
-    <div className={'menu dropdown' + (navOpen ? '' : ' hidden')}>
-      <Button title="Game Info & Credits" inverted="true" to="" onClick={() => {toggleInfo(); setNavOpen(false)}}>
-        <FontAwesomeIcon icon={faCircleInfo} />&nbsp;Game Info
-      </Button>
-      <Button title="Clear Progress" inverted="true" to="" onClick={() => {toggleEraseMenu(); setNavOpen(false)}}>
-        <FontAwesomeIcon icon={faEraser} />&nbsp;Erase
-      </Button>
-      <Button title="Download Progress" inverted="true" to="" onClick={(ev) => {downloadProgress(gameId, gameProgress, ev); setNavOpen(false)}}>
-        <FontAwesomeIcon icon={faDownload} />&nbsp;Download
-      </Button>
-      <Button title="Load Progress from JSON" inverted="true" to="" onClick={() => {toggleUploadMenu(); setNavOpen(false)}}>
-        <FontAwesomeIcon icon={faUpload} />&nbsp;Upload
-      </Button>
-      <Button title="Impressum, privacy policy" inverted="true" to="" onClick={() => {toggleImpressum(); setNavOpen(false)}}>
-        <FontAwesomeIcon icon={faCircleInfo} />&nbsp;Impressum
-      </Button>
-    </div>
-  </div>
-}
-
+/** button to go one level futher.
+ * for the last level, this button turns into a button going back to the welcome page.
+ */
 function NextButton({worldSize, difficulty, completed, setNavOpen}) {
   const gameId = React.useContext(GameIdContext)
   const {worldId, levelId} = React.useContext(WorldLevelIdContext)
@@ -121,6 +79,9 @@ function NextButton({worldSize, difficulty, completed, setNavOpen}) {
   )
 }
 
+/** button to go one level back.
+ * only renders if the current level id is > 0.
+ */
 function PreviousButton({setNavOpen}) {
   const gameId = React.useContext(GameIdContext)
   const {worldId, levelId} = React.useContext(WorldLevelIdContext)
@@ -134,6 +95,7 @@ function PreviousButton({setNavOpen}) {
   </>)
 }
 
+/** button to toggle between editor and typewriter */
 function InputModeButton({setNavOpen, isDropdown}) {
   const {levelId} = React.useContext(WorldLevelIdContext)
   const {typewriterMode, setTypewriterMode, lockInputMode} = React.useContext(InputModeContext)
@@ -156,6 +118,7 @@ function InputModeButton({setNavOpen, isDropdown}) {
   </Button>
 }
 
+/** button to toggle iimpressum popup */
 function ImpressumButton({setNavOpen, toggleImpressum, isDropdown}) {
   return <Button className="btn btn-inverted toggle-width"
     title="information, Impressum, privacy policy" inverted="true" to="" onClick={(ev) => {toggleImpressum(ev); setNavOpen(false)}}>
@@ -164,6 +127,7 @@ function ImpressumButton({setNavOpen, toggleImpressum, isDropdown}) {
   </Button>
 }
 
+/**  button to go back to welcome page */
 function HomeButton({isDropdown}) {
   const gameId = React.useContext(GameIdContext)
   return <Button to={`/${gameId}`} inverted="true" title="back to world selection" id="home-btn">
@@ -172,7 +136,9 @@ function HomeButton({isDropdown}) {
   </Button>
 }
 
-/** only displays a button if `setPageNumber` is set. */
+/** button in mobile level to toggle inventory.
+ * only displays a button if `setPageNumber` is set.
+ */
 function InventoryButton({pageNumber, setPageNumber}) {
   return (setPageNumber &&
     <Button to="" className="btn btn-inverted toggle-width"
@@ -183,6 +149,55 @@ function InventoryButton({pageNumber, setPageNumber}) {
   )
 }
 
+/** the navigation bar on the welcome page */
+export function WelcomeAppBar({pageNumber, setPageNumber, gameInfo, toggleImpressum, toggleEraseMenu, toggleUploadMenu, toggleInfo} : {
+  pageNumber: number,
+  setPageNumber: any,
+  gameInfo: GameInfo,
+  toggleImpressum: any,
+  toggleEraseMenu: any,
+  toggleUploadMenu: any,
+  toggleInfo: any
+}) {
+  const gameId = React.useContext(GameIdContext)
+  const gameProgress = useAppSelector(selectProgress(gameId))
+  const {mobile} = React.useContext(MobileContext)
+  const [navOpen, setNavOpen] = React.useState(false)
+
+  return <div className="app-bar">
+    <div>
+      <Button inverted="false" title="back to games selection" to="/">
+        <FontAwesomeIcon icon={faArrowLeft} />&nbsp;<FontAwesomeIcon icon={faGlobe} />
+      </Button>
+      <span className="app-bar-title"></span>
+    </div>
+    <div>
+      {!mobile && <span className="app-bar-title">{gameInfo?.title}</span>}
+    </div>
+    <div className="nav-btns">
+      {mobile && <MobileNavButtons pageNumber={pageNumber} setPageNumber={setPageNumber} />}
+      <MenuButton navOpen={navOpen} setNavOpen={setNavOpen} />
+    </div>
+    <div className={'menu dropdown' + (navOpen ? '' : ' hidden')}>
+      <Button title="Game Info & Credits" inverted="true" to="" onClick={() => {toggleInfo(); setNavOpen(false)}}>
+        <FontAwesomeIcon icon={faCircleInfo} />&nbsp;Game Info
+      </Button>
+      <Button title="Clear Progress" inverted="true" to="" onClick={() => {toggleEraseMenu(); setNavOpen(false)}}>
+        <FontAwesomeIcon icon={faEraser} />&nbsp;Erase
+      </Button>
+      <Button title="Download Progress" inverted="true" to="" onClick={(ev) => {downloadProgress(gameId, gameProgress, ev); setNavOpen(false)}}>
+        <FontAwesomeIcon icon={faDownload} />&nbsp;Download
+      </Button>
+      <Button title="Load Progress from JSON" inverted="true" to="" onClick={() => {toggleUploadMenu(); setNavOpen(false)}}>
+        <FontAwesomeIcon icon={faUpload} />&nbsp;Upload
+      </Button>
+      <Button title="Impressum, privacy policy" inverted="true" to="" onClick={() => {toggleImpressum(); setNavOpen(false)}}>
+        <FontAwesomeIcon icon={faCircleInfo} />&nbsp;Impressum
+      </Button>
+    </div>
+  </div>
+}
+
 /** the navigation bar in a level */
 export function LevelAppBar({isLoading, levelTitle, toggleImpressum, pageNumber=undefined, setPageNumber=undefined} : {
   isLoading: boolean,