diff --git a/src/Collector/Collector.php b/src/Collector/Collector.php
index 921afe1..155327e 100644
--- a/src/Collector/Collector.php
+++ b/src/Collector/Collector.php
@@ -10,6 +10,8 @@
 use Panaly\Result\Metric;
 use Panaly\Result\Result;
 
+use function assert;
+
 readonly class Collector
 {
     public function __construct(
@@ -22,7 +24,10 @@ public function collect(): Result
     {
         $result = new Result();
         foreach ($this->configurationFile->metricGroups as $executingGroup) {
-            $group = new Group($executingGroup->title);
+            $title = $executingGroup->title;
+            assert($title !== ''); // Ensured by validation of the object
+
+            $group = new Group($title);
 
             foreach ($executingGroup->metrics as $executingMetric) {
                 $metricHandler = $this->runtimeConfiguration->getMetric($executingMetric->identifier);
diff --git a/src/Result/Group.php b/src/Result/Group.php
index c26f108..375dc09 100644
--- a/src/Result/Group.php
+++ b/src/Result/Group.php
@@ -6,7 +6,10 @@
 
 class Group
 {
-    /** @param list<Metric> $metrics */
+    /**
+     * @param non-empty-string $title
+     * @param list<Metric>     $metrics
+     */
     public function __construct(
         private readonly string $title,
         private array $metrics = [],
@@ -29,7 +32,7 @@ public function addMetric(Metric $metric): void
         $this->metrics[] = $metric;
     }
 
-    /** @return array{title: string, metrics: list<array{title: string, value: mixed}>} */
+    /** @return array{title: non-empty-string, metrics: list<array{title: string, value: mixed}>} */
     public function toArray(): array
     {
         $metricsAsArray = [];
diff --git a/src/Result/Result.php b/src/Result/Result.php
index cce307f..627e881 100644
--- a/src/Result/Result.php
+++ b/src/Result/Result.php
@@ -4,11 +4,25 @@
 
 namespace Panaly\Result;
 
+use DateTimeImmutable;
+use DateTimeInterface;
+
 class Result
 {
+    private readonly DateTimeImmutable $createAt;
     /** @var list<Group> */
     private array $groups = [];
 
+    public function __construct()
+    {
+        $this->createAt = new DateTimeImmutable();
+    }
+
+    public function getCreateAt(): DateTimeImmutable
+    {
+        return $this->createAt;
+    }
+
     /** @return list<Group> */
     public function getGroups(): array
     {
@@ -20,12 +34,24 @@ public function addGroup(Group $group): void
         $this->groups[] = $group;
     }
 
-    /** @return list<array{title: string, metrics: list<array{title: string, value: mixed}>}> */
+    /**
+     * @return array{
+     *     createdAt: non-falsy-string,
+     *     groups: list<array{
+     *           title: string,
+     *           metrics: list<array{title: string, value: mixed}>
+     *     }>
+     * }
+     */
     public function toArray(): array
     {
-        $asArray = [];
+        $asArray = [
+            'createdAt' => $this->createAt->format(DateTimeInterface::ATOM),
+            'groups' => [],
+        ];
+
         foreach ($this->groups as $group) {
-            $asArray[] = $group->toArray();
+            $asArray['groups'][] = $group->toArray();
         }
 
         return $asArray;
diff --git a/tests/Result/ResultTest.php b/tests/Result/ResultTest.php
new file mode 100644
index 0000000..c475e6a
--- /dev/null
+++ b/tests/Result/ResultTest.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Panaly\Test\Result;
+
+use DateTimeInterface;
+use Panaly\Result\Result;
+use PHPUnit\Framework\TestCase;
+
+class ResultTest extends TestCase
+{
+    public function testTheResultConvertedToArrayContainsACreationDateTime(): void
+    {
+        $result        = new Result();
+        $resultAsArray = $result->toArray();
+
+        self::assertArrayHasKey('createdAt', $resultAsArray);
+        self::assertIsString($resultAsArray['createdAt']);
+        self::assertSame($result->getCreateAt()->format(DateTimeInterface::ATOM), $resultAsArray['createdAt']);
+    }
+}