diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 00000000..2e286ac3
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,64 @@
+name: Tests
+
+on:
+  push:
+    branches: [ main, '[0-9]+.x' ]
+  pull_request:
+    branches: [ main, '[0-9]+.x' ]
+  workflow_dispatch: # Allow manual triggering on any branch via `gh workflow run tests.yml -r branch-name`
+
+jobs:
+  build:
+    env:
+      FLOW_PATH_ROOT: ../neos-base-distribution
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - php-version: "8.2"
+            neos-version: "9.0"
+          - php-version: "8.3"
+            neos-version: "9.0"
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          extensions: mbstring, xml, json, zlib, iconv, intl, pdo_sqlite, mysql
+
+      - id: composer-cache
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+        shell: bash
+
+      - uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-composer-
+
+      - name: Prepare Neos distribution
+        run: |
+          git clone --depth 1 --branch ${{ matrix.neos-version }} https://github.com/neos/neos-development-distribution.git ${FLOW_PATH_ROOT}
+          cd ${FLOW_PATH_ROOT}
+          composer config --no-plugins allow-plugins.neos/composer-plugin true
+          composer config repositories.package '{ "type": "path", "url": "../neos-seo", "options": { "symlink": false } }'
+          composer require --no-update --no-interaction neos/seo:@dev
+          composer require --dev --no-update --no-interaction phpstan/phpstan:^1.10
+
+      - name: Install dependencies
+        run: |
+          cd ${FLOW_PATH_ROOT}
+          rm -rf composer.lock
+          composer install --no-interaction --no-progress --prefer-dist
+
+      - name: Linting
+        run: |
+          cd ${FLOW_PATH_ROOT}/Packages/Application/Neos.Seo
+          composer run lint:phpstan
diff --git a/Classes/Fusion/XmlSitemapUrlsImplementation.php b/Classes/Fusion/XmlSitemapUrlsImplementation.php
index a1588da8..f558cc64 100644
--- a/Classes/Fusion/XmlSitemapUrlsImplementation.php
+++ b/Classes/Fusion/XmlSitemapUrlsImplementation.php
@@ -25,8 +25,16 @@
 use Neos\Flow\Persistence\Doctrine\PersistenceManager;
 use Neos\Fusion\FusionObjects\AbstractFusionObject;
 use Neos\Media\Domain\Model\ImageInterface;
-use Neos\Utility\Exception\PropertyNotAccessibleException;
 
+/**
+ * @phpstan-type SitemapUrlItem array{
+ *     node: Node,
+ *     lastModificationDateTime: \DateTimeImmutable,
+ *     priority: string,
+ *     images: array<string, ImageInterface>,
+ *     changeFrequency?: true
+ * }
+ */
 class XmlSitemapUrlsImplementation extends AbstractFusionObject
 {
     #[Flow\Inject]
@@ -36,7 +44,7 @@ class XmlSitemapUrlsImplementation extends AbstractFusionObject
     protected PersistenceManager $persistenceManager;
 
     /**
-     * @var array<string, array<int, string>>
+     * @var array<string, list<string>>
      */
     protected array $assetPropertiesByNodeType = [];
 
@@ -47,7 +55,7 @@ class XmlSitemapUrlsImplementation extends AbstractFusionObject
     protected ?Node $startingPoint = null;
 
     /**
-     * @var array|null
+     * @var list<SitemapUrlItem>|null
      */
     protected ?array $items = null;
 
@@ -84,8 +92,7 @@ public function getStartingPoint(): Node
     /**
      * Evaluate this Fusion object and return the result
      *
-     * @return array
-     * @throws PropertyNotAccessibleException
+     * @return list<SitemapUrlItem>
      */
     public function evaluate(): array
     {
@@ -105,7 +112,9 @@ public function evaluate(): array
                 $startingPoint->aggregateId,
                 FindSubtreeFilter::create(nodeTypes: NodeTypeCriteria::create($nodeTypeNames, NodeTypeNames::createEmpty()))
             );
-
+            if (!$subtree) {
+                throw new \RuntimeException(sprintf('The "startingPoint" Node with identifier "%s" doesnt exist anymore.', $startingPoint->aggregateId->value), 1718735861);
+            }
             $this->collectItems($items, $subtree);
             $this->items = $items;
         }
@@ -113,6 +122,9 @@ public function evaluate(): array
         return $this->items;
     }
 
+    /**
+     * @return list<string>
+     */
     private function getAssetPropertiesForNodeType(NodeType $nodeType): array
     {
         if (!array_key_exists($nodeType->name->value, $this->assetPropertiesByNodeType)) {
@@ -136,7 +148,7 @@ private function getAssetPropertiesForNodeType(NodeType $nodeType): array
     }
 
     /**
-     * @throws PropertyNotAccessibleException
+     * @param list<SitemapUrlItem> $items
      */
     protected function collectItems(array &$items, Subtree $subtree): void
     {
@@ -171,7 +183,9 @@ protected function collectItems(array &$items, Subtree $subtree): void
                     $node->aggregateId,
                     FindSubtreeFilter::create(nodeTypes: NodeTypeCriteria::create($nodeTypeNames, NodeTypeNames::createEmpty()))
                 );
-
+                if (!$contentSubtree) {
+                    throw new \RuntimeException(sprintf('The Node with identifier "%s" doesnt exist anymore.', $node->aggregateId->value), 1718735861);
+                }
                 $this->resolveImages($contentSubtree, $item, $nodeTypeManager);
             }
 
@@ -184,10 +198,7 @@ protected function collectItems(array &$items, Subtree $subtree): void
     }
 
     /**
-     * @param Subtree $subtree
-     * @param array & $item
-     * @return void
-     * @throws PropertyNotAccessibleException
+     * @param SitemapUrlItem $item
      */
     protected function resolveImages(Subtree $subtree, array &$item, NodeTypeManager $nodeTypeManager): void
     {
diff --git a/composer.json b/composer.json
index ca8513cd..c1f084e3 100644
--- a/composer.json
+++ b/composer.json
@@ -7,6 +7,9 @@
         "neos/neos": "^9.0",
         "neos/fusion-afx": "^9.0"
     },
+    "scripts": {
+        "lint:phpstan": "../../../bin/phpstan analyse"
+    },
     "autoload": {
         "psr-4": {
             "Neos\\Seo\\": "Classes"
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 00000000..d0cf7bd0
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,4 @@
+parameters:
+    level: 8
+    paths:
+        - Classes