diff --git a/application/Espo/Core/Utils/Client/DevModeJsFileListProvider.php b/application/Espo/Core/Utils/Client/DevModeJsFileListProvider.php
new file mode 100644
index 0000000000..f383177875
--- /dev/null
+++ b/application/Espo/Core/Utils/Client/DevModeJsFileListProvider.php
@@ -0,0 +1,91 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\Utils\Client;
+
+use Espo\Core\{
+    Utils\File\Manager as FileManager,
+};
+
+/**
+ * @internal Also used by the installer w/o DI.
+ */
+class DevModeJsFileListProvider
+{
+    private $fileManager;
+
+    private const LIBS_FILE = 'frontend/libs.json';
+
+    public function __construct(FileManager $fileManager)
+    {
+        $this->fileManager = $fileManager;
+    }
+
+    /**
+     * @return string[]
+     */
+    public function get(): array
+    {
+        $list = [];
+
+        $items = json_decode($this->fileManager->getContents(self::LIBS_FILE));
+
+        foreach ($items as $item) {
+            if (!($item->bundle ?? false)) {
+                continue;
+            }
+
+            $files = $item->files ?? null;
+
+            if ($files !== null) {
+                $list = array_merge(
+                    $list,
+                    $this->getLibFileListFromItems($files)
+                );
+
+                continue;
+            }
+
+            $list[] = $item->src;
+        }
+
+        return $list;
+    }
+
+    private function getLibFileListFromItems(array $items): array
+    {
+        $list = [];
+
+        foreach ($items as $item) {
+            $list[] = $item->src;
+        }
+
+        return $list;
+    }
+}
diff --git a/application/Espo/Core/Utils/ClientManager.php b/application/Espo/Core/Utils/ClientManager.php
index acef1a9706..65fecce178 100644
--- a/application/Espo/Core/Utils/ClientManager.php
+++ b/application/Espo/Core/Utils/ClientManager.php
@@ -31,6 +31,7 @@ namespace Espo\Core\Utils;
 
 use Espo\Core\{
     Utils\File\Manager as FileManager,
+    Utils\Client\DevModeJsFileListProvider,
 };
 
 /**
@@ -52,20 +53,22 @@ class ClientManager
 
     private $basePath = '';
 
-    private const LIBS_FILE = 'frontend/libs.json';
-
     private $libsConfigPath = 'client/cfg/libs.json';
 
+    private $devModeJsFileListProvider;
+
     public function __construct(
         Config $config,
         ThemeManager $themeManager,
         Metadata $metadata,
-        FileManager $fileManager
+        FileManager $fileManager,
+        DevModeJsFileListProvider $devModeJsFileListProvider
     ) {
         $this->config = $config;
         $this->themeManager = $themeManager;
         $this->metadata = $metadata;
         $this->fileManager = $fileManager;
+        $this->devModeJsFileListProvider = $devModeJsFileListProvider;
     }
 
     public function setBasePath(string $basePath): void
@@ -220,37 +223,6 @@ class ClientManager
      */
     private function getDeveloperModeBundleLibFileList(): array
     {
-        $list = [];
-
-        $items = json_decode($this->fileManager->getContents(self::LIBS_FILE));
-
-        foreach ($items as $item) {
-            if (!($item->bundle ?? false)) {
-                continue;
-            }
-
-            $files = $item->files ?? null;
-
-            if ($files !== null) {
-                $list = array_merge($list, $this->getLibFileListFromItems($files));
-
-                continue;
-            }
-
-            $list[] = $item->src;
-        }
-
-        return $list;
-    }
-
-    private function getLibFileListFromItems(array $items): array
-    {
-        $list = [];
-
-        foreach ($items as $item) {
-            $list[] = $item->src;
-        }
-
-        return $list;
+        return $this->devModeJsFileListProvider->get();
     }
 }
diff --git a/install/core/Utils.php b/install/core/Utils.php
index 7dac7e94aa..2f2f831770 100644
--- a/install/core/Utils.php
+++ b/install/core/Utils.php
@@ -31,7 +31,7 @@ class Utils
 {
     static public $actionPath = 'install/core/actions';
 
-    static public function checkActionExists($actionName)
+    static public function checkActionExists(string $actionName): bool
     {
         return in_array($actionName, [
             'saveSettings',
@@ -49,9 +49,7 @@ class Utils
             'step2',
             'step3',
             'step4',
-            'step5'
+            'step5',
         ]);
-
-        return false;
     }
 }
diff --git a/install/core/tpl/index.tpl b/install/core/tpl/index.tpl
index be00b24cf4..1a9cbb09ca 100644
--- a/install/core/tpl/index.tpl
+++ b/install/core/tpl/index.tpl
@@ -6,14 +6,22 @@
         <meta content="utf-8" http-equiv="encoding">
         <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
 
+        {if $isBuild}
         <script type="text/javascript" src="../client/espo.min.js"></script>
+        {else}
+        {foreach from=$libFileList item=file}
+        <script type="text/javascript" src="../{$file}"></script>
+        {/foreach}
+        {/if}
 
         <script type="text/javascript" src="js/install.js"></script>
         <link href="../client/css/espo/hazyblue.css" rel="stylesheet">
         <link href="css/install.css" rel="stylesheet">
         <link rel="shortcut icon" href="../client/img/favicon.ico" type="image/x-icon">
     </head>
+
     <body class='install-body'>
+        <a href="index.tpl"></a>
         <header id="header"></header>
         <div class="container content">
             <div class="col-md-offset-1 col-md-10">
@@ -23,6 +31,7 @@
                 </div>
             </div>
         </div>
+
         <footer class="container">{include file="footer.tpl"}</footer>
     </body>
 </html>
diff --git a/install/index.php b/install/index.php
index 45ca59f7b5..b858cd48d9 100644
--- a/install/index.php
+++ b/install/index.php
@@ -31,9 +31,11 @@ if (session_status() !== \PHP_SESSION_ACTIVE) {
     session_start();
 }
 
-if (file_exists('../bootstrap.php')) {
-    require_once('../bootstrap.php');
-}
+require_once('../bootstrap.php');
+
+use Espo\Core\Utils\Util;
+use Espo\Core\Utils\Client\DevModeJsFileListProvider;
+use Espo\Core\Utils\File\Manager as FileManager;
 
 if (!isset($postData)) {
     require_once('core/PostData.php');
@@ -43,7 +45,7 @@ if (!isset($postData)) {
 
 $allPostData = $postData->getAll();
 
-//action
+// action
 $action = (!empty($allPostData['action']))? $allPostData['action'] : 'main';
 
 require_once('core/Utils.php');
@@ -53,12 +55,19 @@ if (!Utils::checkActionExists($action)) {
 }
 
 // temp save all settings
-$ignoredFields = array('installProcess', 'dbName', 'hostName', 'dbUserName', 'dbUserPass', 'dbDriver');
+$ignoredFields = [
+    'installProcess',
+    'dbName',
+    'hostName',
+    'dbUserName',
+    'dbUserPass',
+    'dbDriver',
+];
 
 if (!empty($allPostData)) {
     foreach ($allPostData as $key => $val) {
         if (!in_array($key, $ignoredFields)) {
-                $_SESSION['install'][$key] = trim($val);
+            $_SESSION['install'][$key] = trim($val);
         }
     }
 }
@@ -69,8 +78,10 @@ $userLang = (!empty($_SESSION['install']['user-lang']))? $_SESSION['install']['u
 require_once 'core/Language.php';
 
 $language = new Language();
+
 $langs = $language->get($userLang);
-$sanitizedLangs = \Espo\Core\Utils\Util::sanitizeHtml($langs);
+
+$sanitizedLangs = Util::sanitizeHtml($langs);
 //END: get user selected language
 
 $config = include('core/config.php');
@@ -99,8 +110,8 @@ if (!$systemHelper->initWritable()) {
 
     $message = $sanitizedLangs['messages']['Bad init Permission'];
     $message = str_replace('{*}', $dir, $message);
-    $message = str_replace('{C}', $systemHelper->getPermissionCommands(array($dir, ''), '775'), $message);
-    $message = str_replace('{CSU}', $systemHelper->getPermissionCommands(array($dir, ''), '775', true), $message);
+    $message = str_replace('{C}', $systemHelper->getPermissionCommands([$dir, ''], '775'), $message);
+    $message = str_replace('{CSU}', $systemHelper->getPermissionCommands([$dir, ''], '775', true), $message);
 
     die($message . "\n");
 }
@@ -116,7 +127,7 @@ $installer = new Installer();
 // check if app was installed
 if ($installer->isInstalled() && !isset($_SESSION['install']['installProcess'])) {
     if (isset($_SESSION['install']['redirected']) && $_SESSION['install']['redirected']) {
-            die('The installation is disabled. It can be enabled in config files.');
+        die('The installation is disabled. It can be enabled in config files.');
     }
 
     $url = "http://".$_SERVER['HTTP_HOST'].$_SERVER['REQUEST_URI'];
@@ -183,14 +194,20 @@ $smarty->assign('config', $config);
 $smarty->assign('installerConfig', $installer->getInstallerConfigData());
 
 if (Utils::checkActionExists($action)) {
-	include $actionFile;
+    include $actionFile;
 }
 
 if (!empty($actionFile) && file_exists('install/core/tpl/' . $tplName)) {
     /* check if EspoCRM is built */
     $isBuilt = file_exists('client/espo.min.js');
 
-    $smarty->assign('isBuilt', $isBuilt);
+    $smarty->assign('isBuilt', true);
+
+    if (!$isBuilt) {
+        $libListProvider = new DevModeJsFileListProvider(new FileManager());
+
+        $smarty->assign('libFileList', $libListProvider->get());
+    }
 
     $smarty->display('index.tpl');
 }