diff --git a/.github/phpstan.neon b/.github/phpstan.neon
new file mode 100644
index 000000000..fa63a3481
--- /dev/null
+++ b/.github/phpstan.neon
@@ -0,0 +1,31 @@
+parameters:
+    ignoreErrors:
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::countByPid\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findByIsListed\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findByIsSortable\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByFeUserId\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByIndexName\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByPid\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByRecordId\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByRoot\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneBySessionId\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByType\(\)\.#'
+            - '#Call to an undefined method Kitodo\\Dlf\\Domain\\Repository\\[a-zA-Z]+Repository::findOneByUid\(\)\.#'
+            - '#Call to an undefined method Psr\\Http\\Message\\RequestFactoryInterface::request\(\)\.#'
+            - '#Call to an undefined method Solarium\\Core\\Query\\DocumentInterface::setField\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\IiifResourceInterface::getHeight\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\IiifResourceInterface::getWidth\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\IiifResourceInterface::getPossibleTextAnnotationContainers\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\IiifResourceInterface::getTextAnnotations\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\ManifestInterface::getOriginalJsonArray\(\)\.#'
+            - '#Call to an undefined method Ubl\\Iiif\\Presentation\\Common\\Model\\Resources\\RangeInterface::getMemberRangesAndRanges\(\)\.#'
+            - '#Constant LOG_SEVERITY_ERROR not found\.#'
+            - '#Constant LOG_SEVERITY_NOTICE not found\.#'
+            - '#Constant LOG_SEVERITY_WARNING not found\.#'
+            - '#Constant TYPO3_MODE not found\.#'
+    level: 5
+    paths:
+        - ../Classes/
+    excludePaths:
+        - ../Classes/Controller/OaiPmhController.php
+    treatPhpDocTypesAsCertain: false
diff --git a/.github/workflows/phpstan.yml b/.github/workflows/phpstan.yml
new file mode 100644
index 000000000..8d8861501
--- /dev/null
+++ b/.github/workflows/phpstan.yml
@@ -0,0 +1,25 @@
+name: PHPStan
+
+on:
+    push:
+      branches: [ "master" ]
+    pull_request:
+      branches: [ "master" ]
+
+jobs:
+  phpstan:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Install dependencies
+        uses: php-actions/composer@v6
+        with:
+          command: update
+          php_version: "7.4"
+
+      - name: PHPStan Static Analysis
+        uses: php-actions/phpstan@v3
+        with:
+          configuration: ./.github/phpstan.neon
diff --git a/Classes/Api/Orcid/Client.php b/Classes/Api/Orcid/Client.php
index b2cb38c10..3c814b70c 100644
--- a/Classes/Api/Orcid/Client.php
+++ b/Classes/Api/Orcid/Client.php
@@ -31,12 +31,12 @@ class Client
     /**
      * @var string constant for API hostname
      **/
-    const HOSTNAME  = 'orcid.org';
+    const HOSTNAME = 'orcid.org';
 
     /**
      * @var string constant for API version
      **/
-    const VERSION   = '3.0';
+    const VERSION = '3.0';
 
     /**
      * @access protected
diff --git a/Classes/Api/Viaf/Client.php b/Classes/Api/Viaf/Client.php
index b4f82e01f..dbe13163c 100644
--- a/Classes/Api/Viaf/Client.php
+++ b/Classes/Api/Viaf/Client.php
@@ -35,8 +35,6 @@ class Client
     protected Logger $logger;
 
     /**
-     * The VIAF API endpoint
-     *
      * @access private
      * @var string The VIAF API endpoint
      **/
@@ -110,7 +108,7 @@ public function getData()
      *
      * @return string
      **/
-    private  function getApiEndpoint(): string
+    private function getApiEndpoint(): string
     {
         return $this->viafUrl . '/' . $this->endpoint;
     }
diff --git a/Classes/Command/BaseCommand.php b/Classes/Command/BaseCommand.php
index 24e1108e6..922cea9c4 100644
--- a/Classes/Command/BaseCommand.php
+++ b/Classes/Command/BaseCommand.php
@@ -191,7 +191,7 @@ protected function getSolrCores(int $pageId): array
      *
      * @access protected
      *
-     * @param Document $doc The document instance
+     * @param Document $document The document instance
      *
      * @return bool true on success, false otherwise
      */
diff --git a/Classes/Command/HarvestCommand.php b/Classes/Command/HarvestCommand.php
index c9293e62f..e62fa04df 100644
--- a/Classes/Command/HarvestCommand.php
+++ b/Classes/Command/HarvestCommand.php
@@ -187,6 +187,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         if (
             !is_array($input->getOption('set'))
             && !empty($input->getOption('set'))
+            && !empty($oai)
         ) {
             $setsAvailable = $oai->listSets();
             foreach ($setsAvailable as $setAvailable) {
@@ -201,9 +202,14 @@ protected function execute(InputInterface $input, OutputInterface $output): int
             }
         }
 
+        $identifiers = [];
         // Get OAI record identifiers to process.
         try {
-            $identifiers = $oai->listIdentifiers('mets', $from, $until, $set);
+            if (!empty($oai)) {
+                $identifiers = $oai->listIdentifiers('mets', $from, $until, $set);
+            } else {
+                $io->error('ERROR: OAI interface does not exist.');
+            }
         } catch (BaseoaipmhException $exception) {
             $this->handleOaiError($exception, $io);
         }
diff --git a/Classes/Common/AbstractDocument.php b/Classes/Common/AbstractDocument.php
index bc13d3ef7..3876d53cb 100644
--- a/Classes/Common/AbstractDocument.php
+++ b/Classes/Common/AbstractDocument.php
@@ -391,7 +391,7 @@ public abstract function getFileMimeType(string $id): string;
      * @param array $settings
      * @param bool $forceReload Force reloading the document instead of returning the cached instance
      *
-     * @return MetsDocument|IiifManifest|null Instance of this class, either MetsDocument or IiifManifest
+     * @return AbstractDocument|null Instance of this class, either MetsDocument or IiifManifest
      */
     public static function &getInstance(string $location, array $settings = [], bool $forceReload = false)
     {
@@ -441,9 +441,11 @@ public static function &getInstance(string $location, array $settings = [], bool
         // Sanitize input.
         $pid = max(intval($settings['storagePid']), 0);
         if ($documentFormat == 'METS') {
-            $instance = new MetsDocument($location, $pid, $xml);
+            $instance = new MetsDocument($pid, $location, $xml, $settings);
         } elseif ($documentFormat == 'IIIF') {
-            $instance = new IiifManifest($location, $pid, $iiif);
+            // TODO: Parameter $preloadedDocument of class Kitodo\Dlf\Common\IiifManifest constructor expects SimpleXMLElement|Ubl\Iiif\Presentation\Common\Model\Resources\IiifResourceInterface, Ubl\Iiif\Presentation\Common\Model\AbstractIiifEntity|null given.
+            // @phpstan-ignore-next-line
+            $instance = new IiifManifest($pid, $location, $iiif);
         }
 
         if (!is_null($instance)) {
@@ -750,10 +752,11 @@ public function getStructureDepth(string $logId)
      * @abstract
      *
      * @param string $location The location URL of the XML file to parse
+     * @param array $settings The extension settings
      *
      * @return void
      */
-    protected abstract function init(string $location): void;
+    abstract protected function init(string $location, array $settings): void;
 
     /**
      * Reuse any document object that might have been already loaded to determine whether document is METS or IIIF
@@ -1086,6 +1089,8 @@ protected function _getRootId(): int
     {
         if (!$this->rootIdLoaded) {
             if ($this->parentId) {
+                // TODO: Parameter $location of static method AbstractDocument::getInstance() expects string, int<min, -1>|int<1, max> given.
+                // @phpstan-ignore-next-line
                 $parent = self::getInstance($this->parentId, ['storagePid' => $this->pid]);
                 $this->rootId = $parent->rootId;
             }
@@ -1168,20 +1173,19 @@ protected function _setCPid(int $value): void
      *
      * @access protected
      *
-     * @param string $location The location URL of the XML file to parse
      * @param int $pid If > 0, then only document with this PID gets loaded
+     * @param string $location The location URL of the XML file to parse
      * @param \SimpleXMLElement|IiifResourceInterface $preloadedDocument Either null or the \SimpleXMLElement
      * or IiifResourceInterface that has been loaded to determine the basic document format.
      *
      * @return void
      */
-    protected function __construct(string $location, int $pid, $preloadedDocument)
+    protected function __construct(int $pid, string $location, $preloadedDocument, array $settings = [])
     {
         $this->pid = $pid;
         $this->setPreloadedDocument($preloadedDocument);
-        $this->init($location);
+        $this->init($location, $settings);
         $this->establishRecordId($pid);
-        return;
     }
 
     /**
diff --git a/Classes/Common/Helper.php b/Classes/Common/Helper.php
index b3c9698d7..1f32b452a 100644
--- a/Classes/Common/Helper.php
+++ b/Classes/Common/Helper.php
@@ -24,9 +24,6 @@
 use TYPO3\CMS\Core\Utility\ArrayUtility;
 use TYPO3\CMS\Core\Utility\GeneralUtility;
 use TYPO3\CMS\Core\Utility\MathUtility;
-use TYPO3\CMS\Extbase\Configuration\ConfigurationManager;
-use TYPO3\CMS\Extbase\Configuration\ConfigurationManagerInterface;
-use TYPO3\CMS\Extbase\Object\ObjectManager;
 use TYPO3\CMS\Extbase\Utility\LocalizationUtility;
 use TYPO3\CMS\Core\Domain\Repository\PageRepository;
 
@@ -149,6 +146,8 @@ public static function checkIdentifier(string $id, string $type): bool
                 if (!preg_match('/\d{8}-\d{1}/i', $id)) {
                     return false;
                 } elseif ($checksum == 10) {
+                    //TODO: Binary operation "+" between string and 1 results in an error.
+                    // @phpstan-ignore-next-line
                     return self::checkIdentifier(($digits + 1) . substr($id, -2, 2), 'SWD');
                 } elseif (substr($id, -1, 1) != $checksum) {
                     return false;
@@ -218,11 +217,10 @@ public static function decrypt(string $encrypted)
      *
      * @static
      *
-     * @param string $content: content of file to read
+     * @param mixed $content content of file to read
      *
      * @return \SimpleXMLElement|false
      */
-    //TODO: make sure that this is called only with string then update
     public static function getXmlFileAsString($content)
     {
         // Don't make simplexml_load_string throw (when $content is an array
@@ -605,7 +603,7 @@ public static function getURN(string $base, string $id): string
         for ($i = 0, $j = strlen($digits); $i < $j; $i++) {
             $checksum += ($i + 1) * intval(substr($digits, $i, 1));
         }
-        $checksum = substr(intval($checksum / intval(substr($digits, -1, 1))), -1, 1);
+        $checksum = substr((string) floor($checksum / (int) substr($digits, -1, 1)), -1, 1);
         return $base . $id . $checksum;
     }
 
@@ -723,7 +721,7 @@ public static function translate(string $indexName, string $table, string $pid):
 
         // Check if "index_name" is an UID.
         if (MathUtility::canBeInterpretedAsInteger($indexName)) {
-            $indexName = self::getIndexNameFromUid($indexName, $table, $pid);
+            $indexName = self::getIndexNameFromUid((int) $indexName, $table, $pid);
         }
         /* $labels already contains the translated content element, but with the index_name of the translated content element itself
          * and not with the $indexName of the original that we receive here. So we have to determine the index_name of the
diff --git a/Classes/Common/IiifManifest.php b/Classes/Common/IiifManifest.php
index 9a1dd3a6b..4554d75a8 100644
--- a/Classes/Common/IiifManifest.php
+++ b/Classes/Common/IiifManifest.php
@@ -408,6 +408,8 @@ public function getFileLocation(string $id): string
         $resource = $this->iiif->getContainedResourceById($id);
         if (isset($resource)) {
             if ($resource instanceof CanvasInterface) {
+                // TODO: Cannot call method getSingleService() on array<Ubl\Iiif\Presentation\Common\Model\Resources\AnnotationInterface>.
+                // @phpstan-ignore-next-line
                 return (!empty($resource->getImageAnnotations()) && $resource->getImageAnnotations()->getSingleService() != null) ? $resource->getImageAnnotations()[0]->getSingleService()->getId() : $id;
             } elseif ($resource instanceof ContentResourceInterface) {
                 return $resource->getSingleService() != null && $resource->getSingleService() instanceof Service ? $resource->getSingleService()->getId() : $id;
@@ -458,6 +460,8 @@ public function getLogicalStructure(string $id, bool $recursive = false): array
         } else {
             $logUnits[] = $this->iiif;
         }
+        // TODO: Variable $logUnits in empty() always exists and is not falsy.
+        // @phpstan-ignore-next-line
         if (!empty($logUnits)) {
             if (!$recursive) {
                 $details = $this->getLogicalStructureInfo($logUnits[0]);
@@ -504,7 +508,7 @@ protected function getLogicalStructureInfo(IiifResourceInterface $resource, bool
         }
         $details['thumbnailId'] = $resource->getThumbnailUrl();
         $details['points'] = '';
-        // Load strucural mapping
+        // Load structural mapping
         $this->_getSmLinks();
         // Load physical structure.
         $this->_getPhysicalStructure();
@@ -516,7 +520,7 @@ protected function getLogicalStructureInfo(IiifResourceInterface $resource, bool
             $startCanvas = $resource->getStartCanvasOrFirstCanvas();
             $canvases = $resource->getAllCanvases();
         }
-        if ($startCanvas != null) {
+        if (isset($startCanvas)) {
             $details['pagination'] = $startCanvas->getLabel();
             $startCanvasIndex = array_search($startCanvas, $this->iiif->getDefaultCanvases());
             if ($startCanvasIndex !== false) {
@@ -681,8 +685,12 @@ public function getMetadata(string $id, int $cPid = 0): array
                     $resArray['format'] > 0 && !empty($resArray['xpath_sorting'])
                     && ($values = $iiifResource->jsonPath($resArray['xpath_sorting']) != null)
                 ) {
+                    // TODO: Call to function is_string() with true will always evaluate to false.
+                    // @phpstan-ignore-next-line
                     if (is_string($values)) {
                         $metadata[$resArray['index_name'] . '_sorting'][0] = [trim((string) $values)];
+                        // TODO: Instanceof between true and Flow\JSONPath\JSONPath will always evaluate to false.
+                        // @phpstan-ignore-next-line
                     } elseif ($values instanceof JSONPath && is_array($values->data()) && count($values->data()) > 1) {
                         $metadata[$resArray['index_name']] = [];
                         foreach ($values->data() as $value) {
@@ -836,7 +844,7 @@ public function getIiif(): IiifResourceInterface
     /**
      * @see AbstractDocument::init()
      */
-    protected function init(string $location): void
+    protected function init(string $location, array $settings = []): void
     {
         $this->logger = GeneralUtility::makeInstance(LogManager::class)->getLogger(static::class);
     }
diff --git a/Classes/Common/Indexer.php b/Classes/Common/Indexer.php
index 083550ffb..f7102281d 100644
--- a/Classes/Common/Indexer.php
+++ b/Classes/Common/Indexer.php
@@ -532,8 +532,8 @@ protected static function processPhysical(Document $document, int $page, array $
     protected static function solrConnect(int $core, int $pid = 0): bool
     {
         // Get Solr instance.
-        // Connect to Solr server.
         $solr = Solr::getInstance($core);
+        // Connect to Solr server.
         if ($solr->ready) {
             self::$solr = $solr;
             // Load indexing configuration if needed.
diff --git a/Classes/Common/MetadataInterface.php b/Classes/Common/MetadataInterface.php
index 5ff6f624e..1de7ca723 100644
--- a/Classes/Common/MetadataInterface.php
+++ b/Classes/Common/MetadataInterface.php
@@ -31,8 +31,9 @@ interface MetadataInterface
      *
      * @param \SimpleXMLElement $xml The XML to extract the metadata from
      * @param array &$metadata The metadata array to fill
+     * @param bool $useExternalApis true if external APIs should be called, false otherwise
      *
      * @return void
      */
-    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata): void;
+    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata, bool $useExternalApis): void;
 }
diff --git a/Classes/Common/MetsDocument.php b/Classes/Common/MetsDocument.php
index 613c32440..8886ef4e5 100644
--- a/Classes/Common/MetsDocument.php
+++ b/Classes/Common/MetsDocument.php
@@ -137,6 +137,12 @@ final class MetsDocument extends AbstractDocument
      */
     protected string $parentHref = '';
 
+    /**
+     * @access protected
+     * @var array the extension settings
+     */
+    protected array $settings = [];
+
     /**
      * This adds metadata from METS structural map to metadata array.
      *
@@ -467,7 +473,7 @@ public function getMetadata(string $id, int $cPid = 0): array
                         class_exists($class)
                         && ($obj = GeneralUtility::makeInstance($class)) instanceof MetadataInterface
                     ) {
-                        $obj->extractMetadata($this->mdSec[$dmdId]['xml'], $metadata);
+                        $obj->extractMetadata($this->mdSec[$dmdId]['xml'], $metadata, $this->settings['useExternalApisForMetadata']);
                     } else {
                         $this->logger->warning('Invalid class/method "' . $class . '->extractMetadata()" for metadata format "' . $this->mdSec[$dmdId]['type'] . '"');
                     }
@@ -711,9 +717,10 @@ public function getStructureDepth(string $logId)
     /**
      * @see AbstractDocument::init()
      */
-    protected function init(string $location): void
+    protected function init(string $location, array $settings): void
     {
         $this->logger = GeneralUtility::makeInstance(LogManager::class)->getLogger(get_class($this));
+        $this->settings = $settings;
         // Get METS node from XML file.
         $this->registerNamespaces($this->xml);
         $mets = $this->xml->xpath('//mets:mets');
@@ -1221,7 +1228,7 @@ public function __wakeup(): void
             $this->asXML = '';
             $this->xml = $xml;
             // Rebuild the unserializable properties.
-            $this->init('');
+            $this->init('', $this->settings);
         } else {
             $this->logger = GeneralUtility::makeInstance(LogManager::class)->getLogger(static::class);
             $this->logger->error('Could not load XML after deserialization');
diff --git a/Classes/Common/Solr/SearchResult/Highlight.php b/Classes/Common/Solr/SearchResult/Highlight.php
index a484c5ac4..b3d5da963 100644
--- a/Classes/Common/Solr/SearchResult/Highlight.php
+++ b/Classes/Common/Solr/SearchResult/Highlight.php
@@ -29,12 +29,6 @@ class Highlight
      */
     private string $id;
 
-    /**
-     * @access private
-     * @var int The parent region's identifier
-     */
-    private int $parentRegionId;
-
     /**
      * @access private
      * @var int The horizontal beginning position of found highlight
@@ -70,7 +64,8 @@ class Highlight
      */
     public function __construct(array $highlight)
     {
-        $this->parentRegionId = $highlight['parentRegionIdx'];
+        // there is also possibility to access parentRegionIdx
+        // $this->parentRegionId = $highlight['parentRegionIdx'];
         $this->xBeginPosition = $highlight['ulx'];
         $this->xEndPosition = $highlight['lrx'];
         $this->yBeginPosition = $highlight['uly'];
diff --git a/Classes/Common/Solr/Solr.php b/Classes/Common/Solr/Solr.php
index 97703a9cd..c3bb6e0d6 100644
--- a/Classes/Common/Solr/Solr.php
+++ b/Classes/Common/Solr/Solr.php
@@ -528,7 +528,7 @@ public function __get(string $var)
             || !method_exists($this, $method)
         ) {
             $this->logger->warning('There is no getter function for property "' . $var . '"');
-            return;
+            return null;
         } else {
             return $this->$method();
         }
diff --git a/Classes/Common/Solr/SolrSearch.php b/Classes/Common/Solr/SolrSearch.php
index ea3b826a9..a76a78f4f 100644
--- a/Classes/Common/Solr/SolrSearch.php
+++ b/Classes/Common/Solr/SolrSearch.php
@@ -210,6 +210,7 @@ public function offsetExists($offset): bool
      *
      * @return mixed
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($offset)
     {
         $idx = $this->result['document_keys'][$offset];
@@ -361,6 +362,7 @@ public function prepare()
         $params = [];
         $matches = [];
         $fields = Solr::getFields();
+        $query = '';
 
         // Set search query.
         if (
@@ -724,7 +726,7 @@ protected function searchSolr($parameters = [], $enableCache = true)
                 // return the coordinates of highlighted search as absolute coordinates
                 $solrRequest->addParam('hl.ocr.absoluteHighlights', 'on');
                 // max amount of snippets for a single page
-                $solrRequest->addParam('hl.snippets', 20);
+                $solrRequest->addParam('hl.snippets', '20');
                 // we store the fulltext on page level and can disable this option
                 $solrRequest->addParam('hl.ocr.trackPages', 'off');
             }
@@ -737,6 +739,8 @@ protected function searchSolr($parameters = [], $enableCache = true)
             }
             $result = $solr->service->createResult($selectQuery, $response);
 
+            // TODO: Call to an undefined method Solarium\Core\Query\Result\ResultInterface::getGrouping().
+            // @phpstan-ignore-next-line
             $uidGroup = $result->getGrouping()->getGroup('uid');
             $resultSet['numberOfToplevels'] = $uidGroup->getNumberOfGroups();
             $resultSet['numFound'] = $uidGroup->getMatches();
diff --git a/Classes/Common/Solr/SolrSearchQuery.php b/Classes/Common/Solr/SolrSearchQuery.php
index 1ab24a327..33419e226 100644
--- a/Classes/Common/Solr/SolrSearchQuery.php
+++ b/Classes/Common/Solr/SolrSearchQuery.php
@@ -55,6 +55,8 @@ public function __construct($solrSearch)
         $this->limit = count($solrSearch);
     }
 
+    // this class contains a lot of methods which are inherited but not implemented
+    // @phpstan-ignore-next-line
     public function getSource() {}
 
     /**
@@ -66,6 +68,8 @@ public function getSource() {}
      *
      * @return array
      */
+    // TODO: Return type (array) of method SolrSearchQuery::execute() should be compatible with return type (iterable<object>&TYPO3\CMS\Extbase\Persistence\QueryResultInterface) of method TYPO3\CMS\Extbase\Persistence\QueryInterface::execute()
+    // @phpstan-ignore-next-line
     public function execute($returnRawQueryResult = false)
     {
         $this->solrSearch->submit($this->offset, $this->limit);
@@ -79,6 +83,7 @@ public function execute($returnRawQueryResult = false)
         return $result;
     }
 
+    // @phpstan-ignore-next-line
     public function setOrderings(array $orderings) {}
 
     /**
@@ -111,27 +116,42 @@ public function setOffset($offset): SolrSearchQuery
         return $this;
     }
 
+    // @phpstan-ignore-next-line
     public function matching($constraint) {}
+    // @phpstan-ignore-next-line
     public function logicalAnd($constraint1) {}
+    // @phpstan-ignore-next-line
     public function logicalOr($constraint1) {}
+    // @phpstan-ignore-next-line
     public function logicalNot(ConstraintInterface $constraint) {}
+    // @phpstan-ignore-next-line
     public function equals($propertyName, $operand, $caseSensitive = true) {}
+    // @phpstan-ignore-next-line
     public function like($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function contains($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function in($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function lessThan($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function lessThanOrEqual($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function greaterThan($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function greaterThanOrEqual($propertyName, $operand) {}
+    // @phpstan-ignore-next-line
     public function getType() {}
     public function setQuerySettings(QuerySettingsInterface $querySettings) {}
+    // @phpstan-ignore-next-line
     public function getQuerySettings() {}
 
     public function count()
-    {
+    {// @phpstan-ignore-next-line
         // TODO?
     }
 
+    // @phpstan-ignore-next-line
     public function getOrderings() {}
 
     /**
@@ -158,8 +178,10 @@ public function getOffset(): int
         return $this->offset;
     }
 
+    // @phpstan-ignore-next-line
     public function getConstraint() {}
     public function isEmpty($propertyName) {}
     public function setSource(SourceInterface $source) {}
+    // @phpstan-ignore-next-line
     public function getStatement() {}
 }
diff --git a/Classes/Controller/AbstractController.php b/Classes/Controller/AbstractController.php
index d946e2cc2..5baf989c1 100644
--- a/Classes/Controller/AbstractController.php
+++ b/Classes/Controller/AbstractController.php
@@ -59,9 +59,9 @@ public function injectDocumentRepository(DocumentRepository $documentRepository)
 
     /**
      * @access protected
-     * @var Document This holds the current document
+     * @var Document|null This holds the current document
      */
-    protected Document $document;
+    protected ?Document $document;
 
     /**
      * @access protected
diff --git a/Classes/Controller/Backend/NewTenantController.php b/Classes/Controller/Backend/NewTenantController.php
index c85b941c5..3d461878f 100644
--- a/Classes/Controller/Backend/NewTenantController.php
+++ b/Classes/Controller/Backend/NewTenantController.php
@@ -436,17 +436,6 @@ public function indexAction(): void
         $this->view->assign('recordInfos', $recordInfos);
     }
 
-    /**
-     * Error function - there is nothing to do at the moment.
-     *
-     * @access public
-     *
-     * @return void
-     */
-    public function errorAction()
-    {
-    }
-
     /**
      * Get language label for given key and language.
      * 
diff --git a/Classes/Controller/BasketController.php b/Classes/Controller/BasketController.php
index d5242e439..e1ba0f8dc 100644
--- a/Classes/Controller/BasketController.php
+++ b/Classes/Controller/BasketController.php
@@ -274,6 +274,8 @@ protected function getBasketData(): Basket
      */
     protected function getEntry(array $data): array
     {
+        // TODO: Call to function is_object() with array will always evaluate to false.
+        // @phpstan-ignore-next-line
         if (is_object($data)) {
             $data = get_object_vars($data);
         }
@@ -330,10 +332,14 @@ protected function getDocumentData(int $id, array $data)
     {
         // get document instance to load further information
         $this->loadDocument((int) $id);
-        if ($this->document) {
+        if (isset($this->document)) {
             // replace url param placeholder
+            // TODO: Parameter #2 $replace of function str_replace expects array|string, int given.
+            // @phpstan-ignore-next-line
             $urlParams = str_replace("##page##", (int) $data['page'], $this->settings['pdfparams']);
             $urlParams = str_replace("##docId##", $this->document->getRecordId(), $urlParams);
+            // TODO: Parameter #2 $replace of function str_replace expects array|string, int given.
+            // @phpstan-ignore-next-line
             $urlParams = str_replace("##startpage##", (int) $data['startpage'], $urlParams);
             if ($data['startpage'] != $data['endpage']) {
                 $urlParams = str_replace("##endpage##", $data['endpage'] === "" ? "" : (int) $data['endpage'], $urlParams);
@@ -450,6 +456,8 @@ protected function addToBasket(array $piVars, Basket $basket): ?Basket
             if (!in_array($arrayKey, $items)) {
                 $items[$arrayKey] = $documentItem;
                 // replace url param placeholder
+                // TODO: Parameter #2 $replace of function str_replace expects array|string, int given.
+                // @phpstan-ignore-next-line
                 $pdfParams = str_replace("##startpage##", $documentItem['startpage'], $this->settings['pdfparams']);
                 $pdfParams = str_replace("##docId##", $this->document->getRecordId(), $pdfParams);
                 $pdfParams = str_replace("##startx##", $documentItem['startX'], $pdfParams);
diff --git a/Classes/Controller/CalendarController.php b/Classes/Controller/CalendarController.php
index c19596039..fea47290d 100644
--- a/Classes/Controller/CalendarController.php
+++ b/Classes/Controller/CalendarController.php
@@ -81,10 +81,8 @@ public function mainAction(): void
             case 'newspaper':
             case 'ephemera':
                 $this->forward('years', null, null, $this->requestData);
-                break;
             case 'year':
                 $this->forward('calendar', null, null, $this->requestData);
-                break;
             case 'issue':
             default:
                 break;
@@ -289,10 +287,14 @@ public function yearsAction(): void
                 $max = $yearArray[count($yearArray) - 1]['title'];
                 // if we have an actual documentId it should be used, otherwise leave empty
                 for ($i = 0; $i < $max - $min + 1; $i++) {
+                    // TODO: Binary operation "+" between (array|string) and int<0, max> results in an error.
+                    // @phpstan-ignore-next-line
                     $key = array_search($min + $i, array_column($yearArray, 'title'));
                     if (is_int($key)) {
                         $yearFilled[] = $yearArray[$key];
                     } else {
+                        // TODO: Binary operation "+" between (array|string) and int<0, max> results in an error.
+                        // @phpstan-ignore-next-line
                         $yearFilled[] = ['title' => $min+$i, 'documentId' => ''];
                     }
                 }
diff --git a/Classes/Controller/CollectionController.php b/Classes/Controller/CollectionController.php
index 4d332d98f..d329ffac1 100644
--- a/Classes/Controller/CollectionController.php
+++ b/Classes/Controller/CollectionController.php
@@ -137,6 +137,8 @@ public function listAction(): void
 
             // Generate random but unique array key taking priority into account.
             do {
+                //TODO: Offset 'priority' does not exist on array{titles: array<int|string, mixed>, volumes: array<int|string, mixed>}.
+                // @phpstan-ignore-next-line
                 $_key = ($collectionInfo['priority'] * 1000) + mt_rand(0, 1000);
             } while (!empty($processedCollections[$_key]));
 
diff --git a/Classes/Controller/ListViewController.php b/Classes/Controller/ListViewController.php
index fc882db5e..6a7e497e2 100644
--- a/Classes/Controller/ListViewController.php
+++ b/Classes/Controller/ListViewController.php
@@ -83,7 +83,7 @@ public function mainAction(): void
         $collection = null;
         if ($this->searchParams['collection']) {
             foreach(explode(',', $this->searchParams['collection']) as $collectionEntry) {
-                $collection[] = $this->collectionRepository->findByUid($collectionEntry);
+                $collection[] = $this->collectionRepository->findByUid((int) $collectionEntry);
             }
         }
 
@@ -92,6 +92,8 @@ public function mainAction(): void
         if (empty($currentPage)) {
             $currentPage = 1;
         }
+        //TODO: Undefined variable: $widgetPage
+        // @phpstan-ignore-next-line
         $GLOBALS['TSFE']->fe_user->setKey('ses', 'widgetPage', $widgetPage);
 
         // get all sortable metadata records
@@ -103,6 +105,7 @@ public function mainAction(): void
         $solrResults = null;
         $numResults = 0;
         if (is_array($this->searchParams) && !empty($this->searchParams)) {
+            // @phpstan-ignore-next-line
             $solrResults = $this->documentRepository->findSolrByCollection($collection ? : null, $this->settings, $this->searchParams, $listedMetadata);
             $numResults = $solrResults->getNumFound();
 
diff --git a/Classes/Controller/MetadataController.php b/Classes/Controller/MetadataController.php
index ec49faf99..008ebf024 100644
--- a/Classes/Controller/MetadataController.php
+++ b/Classes/Controller/MetadataController.php
@@ -116,12 +116,14 @@ public function mainAction(): void
         $metadata = $this->getMetadata();
         $topLevelId = $this->currentDocument->toplevelId;
         // Get titledata?
-        if (empty($metadata) || ($this->settings['rootline'] == 1 && $metadata[0]['_id'] != $topLevelId)) {
+        if (!$metadata || ($this->settings['rootline'] == 1 && $metadata[0]['_id'] != $topLevelId)) {
+            // @phpstan-ignore-next-line
             $data = $useOriginalIiifManifestMetadata ? $this->currentDocument->getManifestMetadata($topLevelId, $this->settings['storagePid']) : $this->currentDocument->getTitledata($this->settings['storagePid']);
             $data['_id'] = $topLevelId;
             array_unshift($metadata, $data);
         }
-        if (empty($metadata)) {
+        // @phpstan-ignore-next-line
+        if (!$metadata) {
             $this->logger->warning('No metadata found for document with UID ' . $this->document->getUid());
             return;
         }
@@ -229,6 +231,8 @@ private function buildIiifData(array $metadata): array
     private function buildIiifDataGroup(string $label, string $value): array
     {
         // NOTE: Labels are to be escaped in Fluid template
+        // TODO: Variable $scheme might not be defined.
+        // @phpstan-ignore-next-line
         if (IRI::isAbsoluteIri($value) && ($scheme = (new IRI($value))->getScheme()) == 'http' || $scheme == 'https') {
             //TODO: should really label be converted to empty string if equal to value?
             $label = $value == $label ? '' : $label;
@@ -431,6 +435,7 @@ private function getMetadataForIds(array $id, array $metadata): array
         $useOriginalIiifManifestMetadata = $this->settings['originalIiifMetadata'] == 1 && $this->currentDocument instanceof IiifManifest;
         foreach ($id as $sid) {
             if ($useOriginalIiifManifestMetadata) {
+                // @phpstan-ignore-next-line
                 $data = $this->currentDocument->getManifestMetadata($sid, $this->settings['storagePid']);
             } else {
                 $data = $this->currentDocument->getMetadata($sid, $this->settings['storagePid']);
diff --git a/Classes/Controller/NavigationController.php b/Classes/Controller/NavigationController.php
index 19b873720..219e4eb7a 100644
--- a/Classes/Controller/NavigationController.php
+++ b/Classes/Controller/NavigationController.php
@@ -87,6 +87,8 @@ public function mainAction(): void
             $searchSessionParameters = $GLOBALS['TSFE']->fe_user->getKey('ses', 'search');
             $widgetPage = $GLOBALS['TSFE']->fe_user->getKey('ses', 'widgetPage');
 
+            //TODO: If condition is always true.
+            // @phpstan-ignore-next-line
             if ($searchSessionParameters) {
                 $lastSearchArguments = [
                     'tx_dlf_listview' => [
diff --git a/Classes/Controller/SearchController.php b/Classes/Controller/SearchController.php
index 74c45f9c7..feffa9cb9 100644
--- a/Classes/Controller/SearchController.php
+++ b/Classes/Controller/SearchController.php
@@ -370,7 +370,7 @@ private function addCollectionsQuery(string $query): string
         $collections = null;
         if ($this->searchParams['collection']) {
             foreach (explode(',', $this->searchParams['collection']) as $collectionEntry) {
-                $collections[] = $this->collectionRepository->findByUid($collectionEntry);
+                $collections[] = $this->collectionRepository->findByUid((int) $collectionEntry);
             }
         }
         if ($collections) {
diff --git a/Classes/Domain/Model/Metadata.php b/Classes/Domain/Model/Metadata.php
index 74910e0d6..a61b0dcd1 100644
--- a/Classes/Domain/Model/Metadata.php
+++ b/Classes/Domain/Model/Metadata.php
@@ -148,7 +148,7 @@ public function getL18nParent(): Metadata
     }
 
     /**
-     * @param int $l18nParent
+     * @param Metadata $l18nParent
      */
     public function setL18nParent(Metadata $l18nParent): void
     {
diff --git a/Classes/Domain/Model/Structure.php b/Classes/Domain/Model/Structure.php
index 3bea2568c..1a3145bdb 100644
--- a/Classes/Domain/Model/Structure.php
+++ b/Classes/Domain/Model/Structure.php
@@ -75,7 +75,7 @@ public function getL18nParent(): Structure
     }
 
     /**
-     * @param int $l18nParent
+     * @param Structure $l18nParent
      */
     public function setL18nParent(Structure $l18nParent): void
     {
diff --git a/Classes/Domain/Repository/CollectionRepository.php b/Classes/Domain/Repository/CollectionRepository.php
index 6774f00d0..c57e0eebd 100644
--- a/Classes/Domain/Repository/CollectionRepository.php
+++ b/Classes/Domain/Repository/CollectionRepository.php
@@ -34,6 +34,8 @@ class CollectionRepository extends Repository
      * @access protected
      * @var array Set the default ordering. This is applied to findAll(), too.
      */
+    // TODO: PHPDoc type array of property CollectionRepository::$defaultOrderings is not covariant with 'ASC'|'DESC'> of overridden property TYPO3\CMS\Extbase\Persistence\Repository::$defaultOrderings.
+    // @phpstan-ignore-next-line
     protected $defaultOrderings = [
         'label' => QueryInterface::ORDER_ASCENDING,
     ];
diff --git a/Classes/Domain/Repository/DocumentRepository.php b/Classes/Domain/Repository/DocumentRepository.php
index 58cc653bf..6544b57dc 100644
--- a/Classes/Domain/Repository/DocumentRepository.php
+++ b/Classes/Domain/Repository/DocumentRepository.php
@@ -500,7 +500,7 @@ public function getOaiDocumentList($documentsToProcess): Result
      * @access public
      *
      * @param array $uids
-     * @param array $checkPartof Whether or not to also match $uids against partof.
+     * @param bool $checkPartof Whether or not to also match $uids against partof.
      *
      * @return array
      */
@@ -572,7 +572,7 @@ public function findChildrenOfEach(array $uids)
      *
      * @access public
      *
-     * @param QueryResult|Collection $collection
+     * @param QueryResult|Collection|null $collection
      * @param array $settings
      * @param array $searchParams
      * @param QueryResult $listedMetadata
diff --git a/Classes/ExpressionLanguage/DocumentTypeFunctionProvider.php b/Classes/ExpressionLanguage/DocumentTypeFunctionProvider.php
index ee27d4c59..fbeabb655 100644
--- a/Classes/ExpressionLanguage/DocumentTypeFunctionProvider.php
+++ b/Classes/ExpressionLanguage/DocumentTypeFunctionProvider.php
@@ -43,7 +43,7 @@ class DocumentTypeFunctionProvider implements ExpressionFunctionProviderInterfac
      *
      * @return ExpressionFunction[] An array of Function instances
      */
-    public function getFunctions()
+    public function getFunctions(): array
     {
         return [
             $this->getDocumentTypeFunction(),
@@ -53,10 +53,10 @@ public function getFunctions()
     /**
      * This holds the current document
      *
-     * @var Document
+     * @var Document|null
      * @access protected
      */
-    protected Document $document;
+    protected ?Document $document;
 
     /**
      * @var ConfigurationManager
diff --git a/Classes/Format/AudioVideoMD.php b/Classes/Format/AudioVideoMD.php
index 3cd4ec93a..9ac90132f 100644
--- a/Classes/Format/AudioVideoMD.php
+++ b/Classes/Format/AudioVideoMD.php
@@ -34,22 +34,29 @@ class AudioVideoMD implements MetadataInterface
      *
      * @param \SimpleXMLElement $xml The XML to extract the metadata from
      * @param array &$metadata The metadata array to fill
+     * @param bool $useExternalApis true if external APIs should be called, false otherwise
      *
      * @return void
      */
-    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata): void
+    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata, bool $useExternalApis = false): void
     {
         $xml->registerXPathNamespace('audiomd', 'http://www.loc.gov/audioMD/');
         $xml->registerXPathNamespace('videomd', 'http://www.loc.gov/videoMD/');
 
-        if (!empty($audioDuration = (string) $xml->xpath('./audiomd:audioInfo/audiomd:duration')[0])) {
+        $audioDuration = (string) $xml->xpath('./audiomd:audioInfo/audiomd:duration')[0];
+        if (!empty($audioDuration)) {
             $metadata['audio_duration'] = [$audioDuration];
         }
 
-        if (!empty($videoDuration = (string) $xml->xpath('./videomd:videoInfo/videomd:duration')[0])) {
+        $videoDuration = (string) $xml->xpath('./videomd:videoInfo/videomd:duration')[0];
+        if (!empty($videoDuration)) {
             $metadata['video_duration'] = [$videoDuration];
         }
 
         $metadata['duration'] = $metadata['video_duration'] ?: $metadata['audio_duration'] ?: [];
+
+        if ($useExternalApis) {
+            // TODO?
+        }
     }
 }
diff --git a/Classes/Format/Mods.php b/Classes/Format/Mods.php
index eca0b2764..cc63962e9 100644
--- a/Classes/Format/Mods.php
+++ b/Classes/Format/Mods.php
@@ -38,6 +38,12 @@ class Mods implements MetadataInterface
      **/
     private $metadata;
 
+    /**
+     * @access private
+     * @var bool The metadata array
+     **/
+    private $useExternalApis;
+
     /**
      * This extracts the essential MODS metadata from XML
      *
@@ -45,13 +51,15 @@ class Mods implements MetadataInterface
      *
      * @param \SimpleXMLElement $xml The XML to extract the metadata from
      * @param array &$metadata The metadata array to fill
+     * @param bool $useExternalApis true if external APIs should be called, false otherwise
      *
      * @return void
      */
-    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata): void
+    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata, bool $useExternalApis): void
     {
         $this->xml = $xml;
         $this->metadata = $metadata;
+        $this->useExternalApis = $useExternalApis;
 
         $this->xml->registerXPathNamespace('mods', 'http://www.loc.gov/mods/v3');
 
@@ -84,7 +92,7 @@ private function getAuthors(): void
                 $authors[$i]->registerXPathNamespace('mods', 'http://www.loc.gov/mods/v3');
 
                 $identifier = $authors[$i]->xpath('./mods:name/mods:nameIdentifier[@type="orcid"]');
-                if ($this->settings['useExternalApisForMetadata'] && !empty((string) $identifier[0])) {
+                if ($this->useExternalApis && !empty((string) $identifier[0])) {
                     $this->getAuthorFromOrcidApi((string) $identifier[0], $authors, $i);
                 } else {
                     $this->getAuthorFromXml($authors, $i);
@@ -207,7 +215,7 @@ private function getHolders(): void
                 $holders[$i]->registerXPathNamespace('mods', 'http://www.loc.gov/mods/v3');
 
                 $identifier = $holders[$i]->xpath('./mods:name/mods:nameIdentifier[@type="viaf"]');
-                if ($this->settings['useExternalApisForMetadata'] && !empty((string) $identifier[0])) {
+                if ($this->useExternalApis && !empty((string) $identifier[0])) {
                     $this->getHolderFromViafApi((string) $identifier[0], $holders, $i);
                 } else {
                     $this->getHolderFromXml($holders, $i);
diff --git a/Classes/Format/TeiHeader.php b/Classes/Format/TeiHeader.php
index 0dcb05719..37680ac49 100644
--- a/Classes/Format/TeiHeader.php
+++ b/Classes/Format/TeiHeader.php
@@ -31,10 +31,11 @@ class TeiHeader implements MetadataInterface
      *
      * @param \SimpleXMLElement $xml The XML to extract the metadata from
      * @param array &$metadata The metadata array to fill
+     * @param bool $useExternalApis true if external APIs should be called, false otherwise
      *
      * @return void
      */
-    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata): void
+    public function extractMetadata(\SimpleXMLElement $xml, array &$metadata, bool $useExternalApis = false): void
     {
         $xml->registerXPathNamespace('teihdr', 'http://www.tei-c.org/ns/1.0');
     }
diff --git a/Classes/Hooks/DataHandler.php b/Classes/Hooks/DataHandler.php
index b61dca4aa..605af0b84 100644
--- a/Classes/Hooks/DataHandler.php
+++ b/Classes/Hooks/DataHandler.php
@@ -39,9 +39,9 @@ class DataHandler implements LoggerAwareInterface
 
     /**
      * @access protected
-     * @var DocumentRepository
+     * @var DocumentRepository|null
      */
-    protected DocumentRepository $documentRepository;
+    protected ?DocumentRepository $documentRepository;
 
     /**
      * Gets document repository
diff --git a/Classes/Hooks/ItemsProcFunc.php b/Classes/Hooks/ItemsProcFunc.php
index 84482667a..3e0d6dca7 100644
--- a/Classes/Hooks/ItemsProcFunc.php
+++ b/Classes/Hooks/ItemsProcFunc.php
@@ -86,6 +86,8 @@ public function getTyposcriptConfigFromPluginSiteRoot(array $params): void
             $this->logger->error($e->getMessage());
         }
 
+        // TODO: Variable $ts might not be defined.
+        // @phpstan-ignore-next-line
         $typoScriptConfig = $ts->setup;
         $this->storagePid = $typoScriptConfig['plugin.']['tx_dlf.']['persistence.']['storagePid'];
 
@@ -161,10 +163,8 @@ protected function generateList(array &$params, string $fields, string $table, s
             ->orderBy($sorting)
             ->execute();
 
-        while ($resArray = $result->fetch(\PDO::FETCH_NUM)) {
-            if ($resArray) {
-                $params['items'][] = $resArray;
-            }
+        while ($resArray = $result->fetchNumeric()) {
+            $params['items'][] = $resArray;
         }
     }
 }
diff --git a/Classes/Middleware/SearchInDocument.php b/Classes/Middleware/SearchInDocument.php
index bc0803792..bf9b3029d 100644
--- a/Classes/Middleware/SearchInDocument.php
+++ b/Classes/Middleware/SearchInDocument.php
@@ -57,7 +57,7 @@ class SearchInDocument implements MiddlewareInterface
      * @param ServerRequestInterface $request
      * @param RequestHandlerInterface $handler
      *
-     * @return ResponseInterface JSON response of documents
+     * @return ResponseInterface JSON response of search suggestions
      */
     public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
     {
@@ -88,13 +88,14 @@ public function process(ServerRequestInterface $request, RequestHandlerInterface
         if ($this->solr->ready) {
             $result = $this->executeSolrQuery($parameters);
             /** @scrutinizer ignore-call */
-            $output['numFound'] = $result->getNumFound();
+            $output['numFound'] = $result->getNumFound(); // @phpstan-ignore-line
             $data = $result->getData();
             $highlighting = $data['ocrHighlighting'];
 
             $siteFinder = GeneralUtility::makeInstance(SiteFinder::class);
             $site = $siteFinder->getSiteByPageId($parameters['pid']);
 
+            // @phpstan-ignore-next-line
             foreach ($result as $record) {
                 $resultDocument = new ResultDocument($record, $highlighting, $this->fields);
 
@@ -154,7 +155,7 @@ private function executeSolrQuery($parameters)
          // return the coordinates of highlighted search as absolute coordinates
         $solrRequest->addParam('hl.ocr.absoluteHighlights', 'on');
         // max amount of snippets for a single page
-        $solrRequest->addParam('hl.snippets', 40);
+        $solrRequest->addParam('hl.snippets', '40');
         // we store the fulltext on page level and can disable this option
         $solrRequest->addParam('hl.ocr.trackPages', 'off');
 
diff --git a/Classes/Pagination/PageGridPagination.php b/Classes/Pagination/PageGridPagination.php
index 5cdeb65b5..c42c78e60 100644
--- a/Classes/Pagination/PageGridPagination.php
+++ b/Classes/Pagination/PageGridPagination.php
@@ -27,6 +27,7 @@ final class PageGridPagination implements PaginationInterface
 
     public function __construct(PaginatorInterface $paginator)
     {
+        // @phpstan-ignore-next-line
         $this->paginator = $paginator;
     }
 
diff --git a/Classes/Updates/FileLocationUpdater.php b/Classes/Updates/FileLocationUpdater.php
index 086a2e83c..044dcf348 100644
--- a/Classes/Updates/FileLocationUpdater.php
+++ b/Classes/Updates/FileLocationUpdater.php
@@ -104,6 +104,7 @@ public function getDescription(): string
      */
     public function updateNecessary(): bool
     {
+        /** @var int */
         $numRecords = $this->getRecordsFromTable(true);
         if ($numRecords > 0) {
             return true;
@@ -146,6 +147,7 @@ public function executeUpdate(): bool
     {
         $result = true;
         try {
+            /** @var int */
             $numRecords = $this->getRecordsFromTable(true);
             if ($numRecords > 0) {
                 $this->performUpdate();
diff --git a/Tests/Functional/Common/MetsDocumentTest.php b/Tests/Functional/Common/MetsDocumentTest.php
index 2dd222e16..4cfaeef88 100644
--- a/Tests/Functional/Common/MetsDocumentTest.php
+++ b/Tests/Functional/Common/MetsDocumentTest.php
@@ -18,7 +18,7 @@ public function setUp(): void
     protected function doc(string $file)
     {
         $url = 'http://web:8001/Tests/Fixtures/MetsDocument/' . $file;
-        $doc = AbstractDocument::getInstance($url);
+        $doc = AbstractDocument::getInstance($url, ['useExternalApisForMetadata' => 0]);
         $this->assertNotNull($doc);
         return $doc;
     }
diff --git a/Tests/Functional/Common/SolrIndexingTest.php b/Tests/Functional/Common/SolrIndexingTest.php
index 559d69df5..faf2e8c70 100644
--- a/Tests/Functional/Common/SolrIndexingTest.php
+++ b/Tests/Functional/Common/SolrIndexingTest.php
@@ -73,7 +73,7 @@ public function canIndexAndSearchDocument()
         $document->setSolrcore($core->model->getUid());
         $this->persistenceManager->persistAll();
 
-        $doc = AbstractDocument::getInstance($document->getLocation());
+        $doc = AbstractDocument::getInstance($document->getLocation(), ['useExternalApisForMetadata' => 0]);
         $document->setCurrentDocument($doc);
 
         $indexingSuccessful = Indexer::add($document, $this->documentRepository);
diff --git a/Tests/Functional/FunctionalTestCase.php b/Tests/Functional/FunctionalTestCase.php
index 2a7a6523d..869d9a5b1 100644
--- a/Tests/Functional/FunctionalTestCase.php
+++ b/Tests/Functional/FunctionalTestCase.php
@@ -104,6 +104,7 @@ public function setUp(): void
     protected function getDlfConfiguration()
     {
         return [
+            'useExternalApisForMetadata' => 0,
             'fileGrpImages' => 'DEFAULT,MAX',
             'fileGrpThumbs' => 'THUMBS',
             'fileGrpDownload' => 'DOWNLOAD',
diff --git a/composer.json b/composer.json
index 9cb43d99e..9cbe60ab1 100644
--- a/composer.json
+++ b/composer.json
@@ -40,6 +40,7 @@
     "solarium/solarium": "^5.2.0"
   },
   "require-dev": {
+    "phpstan/phpstan": "^1.10.0",
     "spatie/phpunit-watcher": "^1.23.0",
     "typo3/cms-backend": "^10.4.36|^11.5.30",
     "typo3/cms-fluid": "^10.4.36|^11.5.30",