diff --git a/application/Espo/Core/Upgrades/Actions/Base.php b/application/Espo/Core/Upgrades/Actions/Base.php
index f71f2f47ef..0fa0f8bd53 100644
--- a/application/Espo/Core/Upgrades/Actions/Base.php
+++ b/application/Espo/Core/Upgrades/Actions/Base.php
@@ -34,6 +34,8 @@ use Espo\Core\Utils\System;
 use Espo\Core\Utils\Json;
 use Espo\Core\Exceptions\Error;
 
+use Espo\Core\Utils\File\Manager as FileManager;
+
 use Espo\Core\{
     Container,
     Upgrades\ActionManager,
@@ -156,6 +158,9 @@ abstract class Base
         return $this->getContainer()->get('log');
     }
 
+    /**
+     * @return FileManager
+     */
     protected function getFileManager()
     {
         return $this->getContainer()->get('fileManager');
@@ -773,11 +778,12 @@ abstract class Base
     /**
      * Delete temporary package files.
      *
-     * @return boolean
+     * @return bool
      */
     protected function deletePackageFiles()
     {
         $packagePath = $this->getPackagePath();
+
         $res = $this->getFileManager()->removeInDir($packagePath, true);
 
         return $res;
@@ -786,11 +792,12 @@ abstract class Base
     /**
      * Delete temporary package archive.
      *
-     * @return boolean
+     * @return bool
      */
     protected function deletePackageArchive()
     {
         $packageArchive = $this->getPackagePath(true);
+
         $res = $this->getFileManager()->removeFile($packageArchive);
 
         return $res;
diff --git a/application/Espo/Core/Upgrades/Actions/Upgrade/Install.php b/application/Espo/Core/Upgrades/Actions/Upgrade/Install.php
index 8ce9678b5a..64d6751997 100644
--- a/application/Espo/Core/Upgrades/Actions/Upgrade/Install.php
+++ b/application/Espo/Core/Upgrades/Actions/Upgrade/Install.php
@@ -53,15 +53,18 @@ class Install extends \Espo\Core\Upgrades\Actions\Base\Install
     }
 
     /**
-     * Delete temporary package files
+     * Delete temporary package files.
      *
-     * @return boolean
+     * @return bool
      */
     protected function deletePackageFiles()
     {
         $res = parent::deletePackageFiles();
+
         $res &= $this->deletePackageArchive();
 
+        /** @var bool @res */
+
         return $res;
     }
 }
diff --git a/application/Espo/Core/Utils/Database/Helper.php b/application/Espo/Core/Utils/Database/Helper.php
index 01beb219f0..bb5f5e869d 100644
--- a/application/Espo/Core/Utils/Database/Helper.php
+++ b/application/Espo/Core/Utils/Database/Helper.php
@@ -153,7 +153,7 @@ class Helper
      * Create PDO connection.
      *
      * @param array $params
-     * @return PDO|\PDOException
+     * @return PDO|null
      */
     public function createPdoConnection(array $params = null)
     {
diff --git a/application/Espo/Core/Utils/Database/Orm/RelationManager.php b/application/Espo/Core/Utils/Database/Orm/RelationManager.php
index 34efd7bd31..e2d4393a0b 100644
--- a/application/Espo/Core/Utils/Database/Orm/RelationManager.php
+++ b/application/Espo/Core/Utils/Database/Orm/RelationManager.php
@@ -88,14 +88,14 @@ class RelationManager
     }
 
     /**
-    * Get foreign Link
-    *
-    * @param string $parentLinkName
-    * @param array $parentLinkParams
-    * @param array $currentEntityDefs
-    *
-    * @return array - in format array('name', 'params')
-    */
+     * Get foreign link.
+     *
+     * @param string $parentLinkName
+     * @param array $parentLinkParams
+     * @param array $currentEntityDefs
+     *
+     * @return array|false Formatted as ['name', 'params'].
+     */
     private function getForeignLink($parentLinkName, $parentLinkParams, $currentEntityDefs)
     {
         if (isset($parentLinkParams['foreign']) && isset($currentEntityDefs['links'][$parentLinkParams['foreign']])) {
diff --git a/application/Espo/Core/Utils/File/Permission.php b/application/Espo/Core/Utils/File/Permission.php
index d0f43592a8..16d1091a4f 100644
--- a/application/Espo/Core/Utils/File/Permission.php
+++ b/application/Espo/Core/Utils/File/Permission.php
@@ -387,7 +387,7 @@ class Permission
     /**
      * Get default owner user.
      *
-     * @return int owner id.
+     * @return int|false owner id.
      */
     public function getDefaultOwner(bool $usePosix = false)
     {
@@ -538,7 +538,7 @@ class Permission
      *
      * @param string $search
      * @param array $array
-     * @return bool
+     * @return int
      */
     protected function getSearchCount($search, array $array)
     {
diff --git a/application/Espo/Core/Utils/Metadata.php b/application/Espo/Core/Utils/Metadata.php
index e575d8efbc..4b3d5b332d 100644
--- a/application/Espo/Core/Utils/Metadata.php
+++ b/application/Espo/Core/Utils/Metadata.php
@@ -157,7 +157,7 @@ class Metadata
     * @param bool $isJSON
     * @param bool $reload
     *
-    * @return array
+    * @return array|string
     */
     public function getAll(bool $isJSON = false, bool $reload = false)
     {
@@ -384,6 +384,7 @@ class Metadata
     public function saveCustom(string $key1, string $key2, $data): void
     {
         if (is_object($data)) {
+            /** @phpstan-ignore-next-line */
             foreach ($data as $key => $item) {
                 if ($item == new stdClass()) {
                     unset($data->$key);
diff --git a/application/Espo/Core/Utils/Util.php b/application/Espo/Core/Utils/Util.php
index 3e45889643..9cac6745ed 100644
--- a/application/Espo/Core/Utils/Util.php
+++ b/application/Espo/Core/Utils/Util.php
@@ -111,9 +111,8 @@ class Util
      * Convert name from Camel Case format.
      * ex. camelCase to camel-case
      *
-     * @param string | array $name
-     *
-     * @return string
+     * @param string|string[] $name
+     * @return string|string[]
      */
     public static function fromCamelCase($name, $symbol = '_')
     {
@@ -139,9 +138,8 @@ class Util
      * Convert name from Camel Case format to underscore.
      * ex. camelCase to camel_case
      *
-     * @param string | array $name
-     *
-     * @return string
+     * @param string|string[] $name
+     * @return string|string[]
      */
     public static function toUnderScore($name)
     {
@@ -220,7 +218,7 @@ class Util
     {
         $doReindex = false;
 
-        foreach($haystack as $key => $value) {
+        foreach ($haystack as $key => $value) {
             if (is_array($value)) {
                 $haystack[$key] = static::unsetInArrayByValue($needle, $value);
             }
@@ -354,13 +352,15 @@ class Util
     * @param string $prePostFix
     * @param string $type
     *
-    * @return string
+    * @return string|null
     */
     public static function getNaming($name, $prePostFix, $type = 'prefix', $symbol = '_')
     {
         if ($type == 'prefix') {
             return static::toCamelCase($prePostFix.$symbol.$name, $symbol);
-        } else if ($type == 'postfix') {
+        }
+
+        if ($type == 'postfix') {
             return static::toCamelCase($name.$symbol.$prePostFix, $symbol);
         }
 
@@ -372,10 +372,9 @@ class Util
      *
      * @param string $search
      * @param string $replace
-     * @param string|false $array
+     * @param string[]|false $array
      * @param bool $isKeys
-     *
-     * @return array
+     * @return string[]|string
      */
     public static function replaceInArray($search = '', $replace = '', $array = false, $isKeys = true)
     {
@@ -383,14 +382,15 @@ class Util
             return str_replace($search, $replace, $array);
         }
 
-        $newArr = array();
+        $newArr = [];
+
         foreach ($array as $key => $value) {
             $addKey = $key;
-            if ($isKeys) { //Replace keys
+
+            if ($isKeys) {
                 $addKey = str_replace($search, $replace, $key);
             }
 
-            // Recurse
             $newArr[$addKey] = static::replaceInArray($search, $replace, $value, $isKeys);
         }