diff --git a/src/Helper.php b/src/Helper.php
index 817605b..f96bc32 100644
--- a/src/Helper.php
+++ b/src/Helper.php
@@ -20,17 +20,12 @@
  */
 class Helper
 {
-    public static function className()
-    {
-        return get_called_class();
-    }
-
     /**
      * Merges two or more arrays into one recursively.
      * Based on Yii2 yii\helpers\BaseArrayHelper::merge.
      * @return array the merged array
      */
-    public static function mergeConfig()
+    public static function mergeConfig(): array
     {
         $args = func_get_args();
         $res = array_shift($args) ?: [];
@@ -62,7 +57,7 @@ public static function mergeConfig()
      * @param Closure $closure
      * @return string
      */
-    public static function dumpClosure(Closure $closure)
+    public static function dumpClosure(Closure $closure): string
     {
         $res = 'function (';
         $fun = new ReflectionFunction($closure);
@@ -99,7 +94,7 @@ public static function dumpClosure(Closure $closure)
      * @param mixed $value
      * @return string
      */
-    public static function exportVar($value)
+    public static function exportVar($value): string
     {
         $closures = self::collectClosures($value);
         $res = var_export($value, true);
@@ -114,7 +109,7 @@ public static function exportVar($value)
         return $res;
     }
 
-    public static function exportDefines(array $defines)
+    public static function exportDefines(array $defines): string
     {
         $res = '';
         foreach ($defines as $key => $value) {
@@ -131,7 +126,7 @@ public static function exportDefines(array $defines)
      * @param mixed $input will be changed
      * @return array array of found closures
      */
-    private static function collectClosures(&$input)
+    private static function collectClosures(&$input): array
     {
         static $closureNo = 1;
         $closures = [];
diff --git a/src/configs/Config.php b/src/configs/Config.php
index 9075a2c..41d75e7 100644
--- a/src/configs/Config.php
+++ b/src/configs/Config.php
@@ -66,7 +66,7 @@ public function getValues(): array
         return $this->values;
     }
 
-    public function load(array $paths = [])
+    public function load(array $paths = []): self
     {
         $configs = [];
         foreach ($paths as $path) {
@@ -86,7 +86,7 @@ public function load(array $paths = [])
      * @param string $path
      * @return array configuration read from file
      */
-    protected function loadFile($path)
+    protected function loadFile($path): array
     {
         $reader = ReaderFactory::get($this->builder, $path);
 
@@ -98,28 +98,28 @@ protected function loadFile($path)
      * @param mixed $name
      * @param array $configs
      */
-    public function build()
+    public function build(): self
     {
         $this->values = $this->calcValues($this->sources);
 
         return $this;
     }
 
-    public function write()
+    public function write(): self
     {
         $this->writeFile($this->getOutputPath(), $this->values);
 
         return $this;
     }
 
-    protected function calcValues(array $sources)
+    protected function calcValues(array $sources): array
     {
         $values = call_user_func_array([Helper::class, 'mergeConfig'], $sources);
 
         return $this->substituteOutputDirs($values);
     }
 
-    protected function writeFile(string $path, array $data)
+    protected function writeFile(string $path, array $data): void
     {
         $this->writePhpFile($path, $data, true);
     }
@@ -130,7 +130,7 @@ protected function writeFile(string $path, array $data)
      * @param string|array $data
      * @param bool $withEnvAndDefines
      */
-    protected function writePhpFile(string $path, $data, bool $withEnvAndDefines)
+    protected function writePhpFile(string $path, $data, bool $withEnvAndDefines): void
     {
         static::putFile($path, $this->replaceMarkers(implode("\n\n", array_filter([
             'header'  => '<?php',
@@ -141,7 +141,11 @@ protected function writePhpFile(string $path, $data, bool $withEnvAndDefines)
         ]))) . "\n");
     }
 
-    protected function renderVars(array $vars)
+    /**
+     * @param array $vars array to be exported
+     * @return string
+     */
+    protected function renderVars(array $vars): string
     {
         return 'return ' . Helper::exportVar($vars) . ';';
     }
@@ -158,7 +162,7 @@ protected function replaceMarkers(string $content): string
      * @param string $path
      * @param string $content
      */
-    protected static function putFile($path, $content)
+    protected static function putFile($path, $content): void
     {
         if (file_exists($path) && $content === file_get_contents($path)) {
             return;
@@ -176,7 +180,7 @@ protected static function putFile($path, $content)
      * @param array $data
      * @return array
      */
-    public function substituteOutputDirs(array $data)
+    public function substituteOutputDirs(array $data): array
     {
         $dir = static::normalizePath(dirname(dirname(dirname($this->getOutputDir()))));
 
@@ -190,7 +194,7 @@ public function substituteOutputDirs(array $data)
      * @param string $ds directory separator
      * @return string
      */
-    public static function normalizePath($path, $ds = self::UNIX_DS)
+    public static function normalizePath($path, $ds = self::UNIX_DS): string
     {
         return rtrim(strtr($path, '/\\', $ds . $ds), $ds);
     }
@@ -202,7 +206,7 @@ public static function normalizePath($path, $ds = self::UNIX_DS)
      * @param string $alias
      * @return array
      */
-    public static function substitutePaths($data, $dir, $alias)
+    public static function substitutePaths($data, $dir, $alias): array
     {
         foreach ($data as &$value) {
             if (is_string($value)) {
@@ -222,7 +226,7 @@ public static function substitutePaths($data, $dir, $alias)
      * @param string $alias
      * @return string
      */
-    protected static function substitutePath($path, $dir, $alias)
+    protected static function substitutePath($path, $dir, $alias): string
     {
         $end = $dir . self::UNIX_DS;
         $skippable = 0 === strncmp($path, '?', 1) ? '?' : '';
diff --git a/src/configs/Defines.php b/src/configs/Defines.php
index 15fe70a..a5d8235 100644
--- a/src/configs/Defines.php
+++ b/src/configs/Defines.php
@@ -17,7 +17,7 @@
  */
 class Defines extends Config
 {
-    protected function loadFile($path)
+    protected function loadFile($path): array
     {
         parent::loadFile($path);
         if (pathinfo($path, PATHINFO_EXTENSION) !== 'php') {
@@ -37,7 +37,7 @@ public function buildRequires(): string
         return implode("\n", $res);
     }
 
-    protected function writeFile(string $path, array $data)
+    protected function writeFile(string $path, array $data): void
     {
         $this->writePhpFile($path, $this->buildRequires(), false);
     }
diff --git a/src/configs/DotEnv.php b/src/configs/DotEnv.php
index 273d504..40b6843 100644
--- a/src/configs/DotEnv.php
+++ b/src/configs/DotEnv.php
@@ -17,7 +17,7 @@
  */
 class DotEnv extends Config
 {
-    protected function writeFile(string $path, array $data)
+    protected function writeFile(string $path, array $data): void
     {
         $this->writePhpFile($path, $data, false);
     }
diff --git a/src/configs/Params.php b/src/configs/Params.php
index 86c79df..4c9307a 100644
--- a/src/configs/Params.php
+++ b/src/configs/Params.php
@@ -17,12 +17,12 @@
  */
 class Params extends Config
 {
-    protected function calcValues(array $sources)
+    protected function calcValues(array $sources): array
     {
         return $this->pushEnvVars(parent::calcValues($sources));
     }
 
-    protected function pushEnvVars($vars)
+    protected function pushEnvVars($vars): array
     {
         $env = $this->builder->getConfig('dotenv')->getValues();
         if (!empty($vars)) {
diff --git a/src/configs/Rebuild.php b/src/configs/Rebuild.php
index b371bc0..af92420 100644
--- a/src/configs/Rebuild.php
+++ b/src/configs/Rebuild.php
@@ -17,7 +17,7 @@
  */
 class Rebuild extends Config
 {
-    protected function writeFile(string $path, array $data)
+    protected function writeFile(string $path, array $data): void
     {
         static::putFile($path, file_get_contents(__DIR__ . DIRECTORY_SEPARATOR . '__rebuild.php'));
     }
diff --git a/src/configs/System.php b/src/configs/System.php
index 3741710..d982293 100644
--- a/src/configs/System.php
+++ b/src/configs/System.php
@@ -18,29 +18,33 @@
  */
 class System extends Config
 {
-    public function setValue(string $name, $value)
+    public function setValue(string $name, $value): Config
     {
         $this->values[$name] = $value;
+
+        return $this;
     }
 
-    public function setValues(array $values)
+    public function setValues(array $values): Config
     {
         $this->values = $values;
 
         return $this;
     }
 
-    public function mergeValues(array $values)
+    public function mergeValues(array $values): Config
     {
         $this->values = array_merge($this->values, $values);
+
+        return $this;
     }
 
-    protected function writeFile(string $path, array $data)
+    protected function writeFile(string $path, array $data): void
     {
         $this->writePhpFile($path, $data, false);
     }
 
-    public function load(array $paths = [])
+    public function load(array $paths = []): Config
     {
         $path = $this->getOutputPath();
         if (!file_exists($path)) {
@@ -52,7 +56,7 @@ public function load(array $paths = [])
         return $this;
     }
 
-    public function build()
+    public function build(): Config
     {
         $this->values = $this->substituteOutputDirs($this->values);