diff --git a/.github/workflows/on_pull_request.yml b/.github/workflows/on_pull_request.yml
index 2cc318c..c5d649e 100644
--- a/.github/workflows/on_pull_request.yml
+++ b/.github/workflows/on_pull_request.yml
@@ -34,6 +34,8 @@ jobs:
         run: composer install --no-progress --no-suggest --prefer-dist --optimize-autoloader
       - name: PHP CodeSniffer
         run: composer phpcs
+      - name: PHPStan
+        run: composer phpstan
       - name: PHPUnit
         run: composer test
       - name: Install Composer dependencies (without dev)
diff --git a/composer.json b/composer.json
index 312fef6..c81bdfe 100644
--- a/composer.json
+++ b/composer.json
@@ -31,11 +31,13 @@
     ],
     "require-dev": {
         "phpunit/phpunit": "^12",
-        "squizlabs/php_codesniffer": "^3.10"
+        "squizlabs/php_codesniffer": "^3.10",
+        "phpstan/phpstan": "^2"
     },
     "scripts": {
         "test": "phpunit --testdox",
         "phpcs": "phpcs --standard=PSR12 src/ tests/",
-        "phpcbf": "phpcbf --standard=PSR12 src/ tests/"
+        "phpcbf": "phpcbf --standard=PSR12 src/ tests/",
+        "phpstan": "phpstan analyse"
     }
 }
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..1494f51
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,5 @@
+parameters:
+    level: max
+    paths:
+        - src
+        - tests
diff --git a/src/OutputDecorator.php b/src/OutputDecorator.php
index 7e3ab8c..84c6234 100644
--- a/src/OutputDecorator.php
+++ b/src/OutputDecorator.php
@@ -59,9 +59,9 @@ public function resetIndent(): void
      * Prints fatal message
      *
      * @param string $message Message to print
-     * @param mixed ...$params Params for parsing message
+     * @param string|int|float|bool|null ...$params Params for parsing message
      */
-    public function fatal(string $message, ...$params): void
+    public function fatal(string $message, string|int|float|bool|null ...$params): void
     {
         $this->write('<error>' . vsprintf($message, $params) . '</error>', true);
     }
@@ -78,15 +78,18 @@ public function renderIndentString(): string
 
     /**
      * @inheritDoc
+     * @param iterable<string>|string $messages
      */
     public function write(iterable|string $messages, bool $newline = false, int $options = self::OUTPUT_NORMAL): void
     {
         if ($this->indent > 0) {
             $tmpMsg = '';
-            foreach (explode(PHP_EOL, $messages) as $line) {
-                $tmpMsg .= $this->renderIndentString() . $line . PHP_EOL;
+            if (is_string($messages)) {
+                foreach (explode(PHP_EOL, $messages) as $line) {
+                    $tmpMsg .= $this->renderIndentString() . $line . PHP_EOL;
+                }
+                $messages = rtrim($tmpMsg);
             }
-            $messages = rtrim($tmpMsg);
         }
 
         $this->output->write($messages, $newline, $options);
@@ -96,9 +99,9 @@ public function write(iterable|string $messages, bool $newline = false, int $opt
      * Prints success message
      *
      * @param string $message Message to print
-     * @param mixed ...$params Params for parsing message
+     * @param string|int|float|bool|null ...$params Params for parsing message
      */
-    public function success(string $message, ...$params): void
+    public function success(string $message, string|int|float|bool|null ...$params): void
     {
         $this->write('<info>' . vsprintf($message, $params) . '</info>', true);
     }
@@ -107,9 +110,9 @@ public function success(string $message, ...$params): void
      * Prints error message
      *
      * @param string $message Message to print
-     * @param mixed ...$params Params for parsing message
+     * @param string|int|float|bool|null ...$params Params for parsing message
      */
-    public function error(string $message, ...$params): void
+    public function error(string $message, string|int|float|bool|null ...$params): void
     {
         $this->write('<error>' . vsprintf($message, $params) . '</error>', true);
     }
@@ -118,9 +121,9 @@ public function error(string $message, ...$params): void
      * Prints info message
      *
      * @param string $message Message to print
-     * @param mixed ...$params Params for parsing message
+     * @param string|int|float|bool|null ...$params Params for parsing message
      */
-    public function info(string $message, ...$params): void
+    public function info(string $message, string|int|float|bool|null ...$params): void
     {
         $this->write('<comment>' . vsprintf($message, $params) . '</comment>', true);
     }
@@ -129,15 +132,16 @@ public function info(string $message, ...$params): void
      * Prints simple message
      *
      * @param string $message Message to print
-     * @param mixed ...$params Params for parsing message
+     * @param string|int|float|bool|null ...$params Params for parsing message
      */
-    public function msg(string $message, ...$params): void
+    public function msg(string $message, string|int|float|bool|null ...$params): void
     {
         $this->write(vsprintf($message, $params), true);
     }
 
     /**
      * @inheritDoc
+     * @param iterable<string>|string $messages
      */
     public function writeln(iterable|string $messages, int $options = 0): void
     {
diff --git a/tests/OutputDecoratorTest.php b/tests/OutputDecoratorTest.php
index 065d6e9..d6a4dfd 100644
--- a/tests/OutputDecoratorTest.php
+++ b/tests/OutputDecoratorTest.php
@@ -20,6 +20,9 @@ protected function setUp(): void
         parent::setUp();
     }
 
+    /**
+     * @return array<string, array<int, mixed>>
+     */
     public static function getTestData(): array
     {
         return [
@@ -90,6 +93,9 @@ public static function getTestData(): array
         ];
     }
 
+    /**
+     * @param array<int, mixed> $params
+     */
     private function useDecoratorMethod(string $method, string $text, array $params): string
     {
         if (empty($params)) {
@@ -102,6 +108,9 @@ private function useDecoratorMethod(string $method, string $text, array $params)
         return $this->output->fetch();
     }
 
+    /**
+     * @param array<int, mixed> $args
+     */
     #[DataProvider('getTestData')]
     public function testIncrIndent(string $method, string $text, array $args = [], ?string $shouldReturn = null): void
     {
@@ -123,6 +132,9 @@ public function testIncrIndent(string $method, string $text, array $args = [], ?
         $this->assertSame($this->decorator->renderIndentString() . $shouldReturn . PHP_EOL, $buffer);
     }
 
+    /**
+     * @param array<int, mixed> $args
+     */
     #[DataProvider('getTestData')]
     public function testDecrIndent(string $method, string $text, array $args = [], ?string $shouldReturn = null): void
     {
@@ -140,6 +152,9 @@ public function testDecrIndent(string $method, string $text, array $args = [], ?
         $this->assertSame($shouldReturn . PHP_EOL, $buffer);
     }
 
+    /**
+     * @param array<int, mixed> $args
+     */
     #[DataProvider('getTestData')]
     public function testResetIncr(string $method, string $text, array $args = [], ?string $shouldReturn = null): void
     {