diff --git a/_admin.php b/_admin.php
index bd6a0bc..540064d 100644
--- a/_admin.php
+++ b/_admin.php
@@ -37,13 +37,13 @@ $core->addBehavior('themesToolsTabs', ['tweakStoresBehaviors', 'themesToolsTabs'
 class tweakStoresBehaviors
 {
     # create dcstore.xml file on the fly when pack a module
-    public static function packmanBeforeCreatePackage(dcCore $core, $module)
+    public static function packmanBeforeCreatePackage(dcCore $core, array $module): void
     {
         tweakStores::writeXML($module['id'], $module, $core->blog->settings->tweakStores->file_pattern);
     }
 
     # addd some js
-    public static function modulesToolsHeaders(dcCore $core, $plugin)
+    public static function modulesToolsHeaders(dcCore $core, bool $is_plugin): string
     {
         $core->auth->user_prefs->addWorkspace('interface');
 
@@ -58,19 +58,19 @@ class tweakStoresBehaviors
     }
 
     # admin plugins page tab
-    public static function pluginsToolsTabs(dcCore $core)
+    public static function pluginsToolsTabs(dcCore $core): void
     {
         self::modulesToolsTabs($core, $core->plugins->getModules(), explode(',', DC_DISTRIB_PLUGINS), $core->adminurl->get('admin.plugins') . '#tweakStores');
     }
 
     # admin themes page tab
-    public static function themesToolsTabs(dcCore $core)
+    public static function themesToolsTabs(dcCore $core): void
     {
         self::modulesToolsTabs($core, $core->themes->getModules(), explode(',', DC_DISTRIB_THEMES), $core->adminurl->get('admin.blog.theme') . '#tweakStores');
     }
 
     # generic page tab
-    protected static function modulesToolsTabs(dcCore $core, $modules, $excludes, $page_url)
+    protected static function modulesToolsTabs(dcCore $core, array $modules, array $excludes, string $page_url): void
     {
         $core->auth->user_prefs->addWorkspace('interface');
         $user_ui_colorsyntax       = $core->auth->user_prefs->interface->colorsyntax;
@@ -252,7 +252,7 @@ class tweakStoresBehaviors
     }
 
     # create list of module for combo and remove official modules
-    protected static function comboModules($modules, array $excludes)
+    protected static function comboModules(array $modules, array $excludes): array
     {
         $combo = [__('Select a module') => '0'];
         foreach ($modules as $id => $module) {
diff --git a/inc/class.tweakstores.php b/inc/class.tweakstores.php
index f5e3ff4..47d0dae 100644
--- a/inc/class.tweakstores.php
+++ b/inc/class.tweakstores.php
@@ -12,11 +12,14 @@
  */
 class tweakStores
 {
+    /** @var array List of notice messages */
     public static $notice = [];
+
+    /** @var array List of failed messages */
     public static $failed = [];
 
     # taken from lib.moduleslist.php
-    public static function sanitizeModule($id, $module)
+    public static function sanitizeModule(string $id, array $module): array
     {
         $label = empty($module['label']) ? $id : $module['label'];
         $name  = __(empty($module['name']) ? $label : $module['name']);
@@ -62,12 +65,12 @@ class tweakStores
     }
 
     # taken from lib.moduleslist.php
-    public static function sanitizeString($str)
+    public static function sanitizeString(string $str): string
     {
-        return preg_replace('/[^A-Za-z0-9\@\#+_-]/', '', strtolower($str));
+        return (string) preg_replace('/[^A-Za-z0-9\@\#+_-]/', '', strtolower($str));
     }
 
-    public static function parseFilePattern($id, $module, $file_pattern)
+    public static function parseFilePattern(string $id, array $module, string $file_pattern): string
     {
         $module = self::sanitizeModule($id, $module);
 
@@ -88,10 +91,10 @@ class tweakStores
         ));
     }
 
-    public static function generateXML($id, $module, $file_pattern)
+    public static function generateXML(string $id, array $module, string $file_pattern): string
     {
         if (!is_array($module) || empty($module)) {
-            return false;
+            return '';
         }
         $module = self::sanitizeModule($id, $module);
         $rsp    = new xmlTag('module');
@@ -185,7 +188,7 @@ class tweakStores
         return self::prettyXML($res->toXML());
     }
 
-    public static function writeXML($id, $module, $file_pattern)
+    public static function writeXML(string $id, array $module, string $file_pattern): bool
     {
         self::$failed = [];
         if (!$module['root_writable']) {
@@ -215,9 +218,9 @@ class tweakStores
             $dom->formatOutput       = true;
             $dom->loadXML($str);
 
-            return $dom->saveXML();
+            return (string) $dom->saveXML();
         }
 
-        return str_replace('><', ">\n<", $str);
+        return (string) str_replace('><', ">\n<", $str);
     }
 }