diff --git a/src/Exceptions/LanguagesRequestException.php b/src/Exceptions/LanguagesRequestException.php
index fb5e8af..02510ad 100644
--- a/src/Exceptions/LanguagesRequestException.php
+++ b/src/Exceptions/LanguagesRequestException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Exceptions;
 
 use ErrorException;
diff --git a/src/Exceptions/LargeTextException.php b/src/Exceptions/LargeTextException.php
index 3adac23..2db6ae2 100644
--- a/src/Exceptions/LargeTextException.php
+++ b/src/Exceptions/LargeTextException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Exceptions;
 
 use ErrorException;
diff --git a/src/Exceptions/RateLimitException.php b/src/Exceptions/RateLimitException.php
index 25cf592..3f9f756 100644
--- a/src/Exceptions/RateLimitException.php
+++ b/src/Exceptions/RateLimitException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Exceptions;
 
 use ErrorException;
diff --git a/src/Exceptions/TranslationDecodingException.php b/src/Exceptions/TranslationDecodingException.php
index ff50c23..08159e6 100644
--- a/src/Exceptions/TranslationDecodingException.php
+++ b/src/Exceptions/TranslationDecodingException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Exceptions;
 
 use UnexpectedValueException;
diff --git a/src/Exceptions/TranslationRequestException.php b/src/Exceptions/TranslationRequestException.php
index 6d23e5a..b62ea0b 100644
--- a/src/Exceptions/TranslationRequestException.php
+++ b/src/Exceptions/TranslationRequestException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Exceptions;
 
 use ErrorException;
diff --git a/src/GoogleTranslate.php b/src/GoogleTranslate.php
index c5574ca..e13bc2e 100644
--- a/src/GoogleTranslate.php
+++ b/src/GoogleTranslate.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate;
 
 use DOMDocument;
@@ -26,7 +28,7 @@
 class GoogleTranslate
 {
     /**
-     * @var \GuzzleHttp\Client HTTP Client
+     * @var Client HTTP Client
      */
     protected Client $client;
 
diff --git a/src/Tokens/GoogleTokenGenerator.php b/src/Tokens/GoogleTokenGenerator.php
index 4b485ab..5ad360e 100644
--- a/src/Tokens/GoogleTokenGenerator.php
+++ b/src/Tokens/GoogleTokenGenerator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tokens;
 
 /**
@@ -22,7 +24,7 @@ public function generateToken(string $source, string $target, string $text): str
     {
         $tkk = ['406398', 2087938574];
 
-        for ($d = [], $e = 0, $f = 0; $f < $this->length($text); $f++) {
+        for ($d = [], $e = 0, $f = 0; $f < $this->length($text); ++$f) {
             $g = $this->charCodeAt($text, $f);
             if ($g < 128) {
                 $d[$e++] = $g;
diff --git a/src/Tokens/SampleTokenGenerator.php b/src/Tokens/SampleTokenGenerator.php
index 40bc877..f601aab 100644
--- a/src/Tokens/SampleTokenGenerator.php
+++ b/src/Tokens/SampleTokenGenerator.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tokens;
 
 /**
diff --git a/src/Tokens/TokenProviderInterface.php b/src/Tokens/TokenProviderInterface.php
index cd26bb8..636de05 100644
--- a/src/Tokens/TokenProviderInterface.php
+++ b/src/Tokens/TokenProviderInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tokens;
 
 /**
diff --git a/tests/ExceptionTest.php b/tests/ExceptionTest.php
index b50063f..713a57b 100644
--- a/tests/ExceptionTest.php
+++ b/tests/ExceptionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tests;
 
 use ErrorException;
@@ -12,7 +14,7 @@
 use Stichoza\GoogleTranslate\GoogleTranslate;
 use UnexpectedValueException;
 
-class ExceptionTest extends TestCase
+final class ExceptionTest extends TestCase
 {
     public GoogleTranslate $tr;
 
diff --git a/tests/LanguageDetectionTest.php b/tests/LanguageDetectionTest.php
index 1d73a63..30ecc16 100644
--- a/tests/LanguageDetectionTest.php
+++ b/tests/LanguageDetectionTest.php
@@ -1,11 +1,13 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tests;
 
 use PHPUnit\Framework\TestCase;
 use Stichoza\GoogleTranslate\GoogleTranslate;
 
-class LanguageDetectionTest extends TestCase
+final class LanguageDetectionTest extends TestCase
 {
     public GoogleTranslate $tr;
 
diff --git a/tests/SupportedLanguagesTest.php b/tests/SupportedLanguagesTest.php
index ba9ec50..b2b0ac3 100644
--- a/tests/SupportedLanguagesTest.php
+++ b/tests/SupportedLanguagesTest.php
@@ -1,11 +1,13 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tests;
 
 use PHPUnit\Framework\TestCase;
 use Stichoza\GoogleTranslate\GoogleTranslate;
 
-class SupportedLanguagesTest extends TestCase
+final class SupportedLanguagesTest extends TestCase
 {
     public GoogleTranslate $tr;
 
diff --git a/tests/TranslationTest.php b/tests/TranslationTest.php
index f7c6dd0..ee0bdab 100644
--- a/tests/TranslationTest.php
+++ b/tests/TranslationTest.php
@@ -1,11 +1,13 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tests;
 
 use PHPUnit\Framework\TestCase;
 use Stichoza\GoogleTranslate\GoogleTranslate;
 
-class TranslationTest extends TestCase
+final class TranslationTest extends TestCase
 {
     public GoogleTranslate $tr;
 
diff --git a/tests/UtilityTest.php b/tests/UtilityTest.php
index bd96699..dc20867 100644
--- a/tests/UtilityTest.php
+++ b/tests/UtilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Stichoza\GoogleTranslate\Tests;
 
 use Exception;
@@ -8,7 +10,7 @@
 use ReflectionMethod;
 use Stichoza\GoogleTranslate\GoogleTranslate;
 
-class UtilityTest extends TestCase
+final class UtilityTest extends TestCase
 {
     public GoogleTranslate $tr;