diff --git a/src/Api/Skill.php b/src/Api/Skill.php
index b952759..730abaa 100644
--- a/src/Api/Skill.php
+++ b/src/Api/Skill.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Api;
 
 /*
diff --git a/src/Api/SkillSet.php b/src/Api/SkillSet.php
index dfded92..f54b225 100644
--- a/src/Api/SkillSet.php
+++ b/src/Api/SkillSet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Api;
 
 /*
diff --git a/src/Constants/VerificationTypes.php b/src/Constants/VerificationTypes.php
index 163528e..4341248 100644
--- a/src/Constants/VerificationTypes.php
+++ b/src/Constants/VerificationTypes.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 define('VERIFICATION_SELF', 'self');
 define('VERIFICATION_EDUCATIONAL', 'education');
 define('VERIFICATION_BUSINESS', 'business');
diff --git a/src/Entity/Skill.php b/src/Entity/Skill.php
index 145e70d..864c143 100644
--- a/src/Entity/Skill.php
+++ b/src/Entity/Skill.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Entity;
 
 /*
diff --git a/src/Entity/SkillSet.php b/src/Entity/SkillSet.php
index 35bfc69..18a261b 100644
--- a/src/Entity/SkillSet.php
+++ b/src/Entity/SkillSet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Entity;
 
 /*
diff --git a/tests/Unit/Api/SkillSetTest.php b/tests/Unit/Api/SkillSetTest.php
index c04259e..2368c77 100644
--- a/tests/Unit/Api/SkillSetTest.php
+++ b/tests/Unit/Api/SkillSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Tests\Unit\Api;
 
 /*
diff --git a/tests/Unit/Api/SkillTest.php b/tests/Unit/Api/SkillTest.php
index 536a1cf..55a0517 100644
--- a/tests/Unit/Api/SkillTest.php
+++ b/tests/Unit/Api/SkillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Tests\Unit\Api;
 
 /*
diff --git a/tests/Unit/Entity/SkillSetTest.php b/tests/Unit/Entity/SkillSetTest.php
index b3af901..8641d50 100644
--- a/tests/Unit/Entity/SkillSetTest.php
+++ b/tests/Unit/Entity/SkillSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Tests\Unit\Entity;
 
 /*
diff --git a/tests/Unit/Entity/SkillTest.php b/tests/Unit/Entity/SkillTest.php
index 2964cb6..24c839f 100644
--- a/tests/Unit/Entity/SkillTest.php
+++ b/tests/Unit/Entity/SkillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace SkillDisplay\PHPToolKit\Tests\Unit\Entity;
 
 /*