diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index dd4f232..415e0b3 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -2,7 +2,7 @@
     "name": "multi-downloader-client",
     "image": "rg.fr-par.scw.cloud/kubernetes/devcontainer:php-8.3",
     "containerEnv": {
-
+        "MULTI_DOWNLOADER_API_KEY": "YOUR_API_KEY"
     },
     "customizations": {
         "vscode": {
diff --git a/src/MultiDownloaderClient.php b/src/MultiDownloaderClient.php
index ae93ef7..d4e1d20 100644
--- a/src/MultiDownloaderClient.php
+++ b/src/MultiDownloaderClient.php
@@ -4,4 +4,16 @@ namespace Nwb\MultiDownloaderClient;
 
 class MultiDownloaderClient
 {
+    private string $apiKey;
+
+    public function __construct(string $apiKey = null)
+    {
+        $apiKey = $apiKey ?? getenv('MULTI_DOWNLOADER_API_KEY');
+
+        if (!$apiKey) {
+            throw new \InvalidArgumentException('API key is required');
+        }
+
+        $this->apiKey = $apiKey;
+    }
 }
diff --git a/tests/ModelLibPhpTest.php b/tests/ModelLibPhpTest.php
deleted file mode 100644
index 1797bac..0000000
--- a/tests/ModelLibPhpTest.php
+++ /dev/null
@@ -1,14 +0,0 @@
-<?php
-
-include __DIR__ . '/../vendor/autoload.php';
-
-use Nwb\MultiDownloaderClient\MultiDownloaderClient;
-use PHPUnit\Framework\TestCase;
-
-class MultiDownloaderClienTest extends TestCase
-{
-    public function testHello()
-    {
-        $client = new MultiDownloaderClient();
-    }
-}
diff --git a/tests/MultiDownloaderClientTest.php b/tests/MultiDownloaderClientTest.php
new file mode 100644
index 0000000..b7d4387
--- /dev/null
+++ b/tests/MultiDownloaderClientTest.php
@@ -0,0 +1,45 @@
+<?php
+
+include __DIR__ . '/../vendor/autoload.php';
+
+use Nwb\MultiDownloaderClient\MultiDownloaderClient;
+use PHPUnit\Framework\TestCase;
+
+class MultiDownloaderClientTest extends TestCase
+{
+    public static function getProperty($object, $property)
+    {
+        $reflectedClass = new \ReflectionClass($object);
+        $reflection = $reflectedClass->getProperty($property);
+        $reflection->setAccessible(true);
+
+        return $reflection->getValue($object);
+    }
+
+    public function testApiKeyEnv()
+    {
+        putenv('MULTI_DOWNLOADER_API_KEY=1234567890');
+
+        $client = new MultiDownloaderClient();
+        $apiKey = self::getProperty($client, 'apiKey');
+        $this->assertEquals('1234567890', $apiKey);
+    }
+
+    public function testApiKeyParam()
+    {
+        $client = new MultiDownloaderClient('test_key');
+
+        $apiKey = self::getProperty($client, 'apiKey');
+        $this->assertEquals('test_key', $apiKey);
+    }
+
+    public function testApiKeyMissing()
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('API key is required');
+
+        putenv('MULTI_DOWNLOADER_API_KEY');
+
+        new MultiDownloaderClient();
+    }
+}