diff --git a/core/modules/media_library/src/Form/AddFormBase.php b/core/modules/media_library/src/Form/AddFormBase.php
index ffa20acfbf..6349a3e51d 100644
--- a/core/modules/media_library/src/Form/AddFormBase.php
+++ b/core/modules/media_library/src/Form/AddFormBase.php
@@ -20,7 +20,7 @@
 use Drupal\media\MediaInterface;
 use Drupal\media\MediaTypeInterface;
 use Drupal\media_library\Ajax\UpdateSelectionCommand;
-use Drupal\media_library\MediaLibraryUiBuilder;
+use Drupal\media_library\MediaLibraryUiBuilderInterface;
 use Drupal\media_library\OpenerResolverInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;

@@ -39,9 +39,9 @@ abstract class AddFormBase extends FormBase implements BaseFormIdInterface, Trus
   /**
    * The media library UI builder.
    *
-   * @var \Drupal\media_library\MediaLibraryUiBuilder
+   * @var \Drupal\media_library\MediaLibraryUiBuilderInterface
    */
-  protected $libraryUiBuilder;
+  protected MediaLibraryUiBuilderInterface $libraryUiBuilder;

   /**
    * The type of media items being created by this form.
@@ -69,12 +69,12 @@ abstract class AddFormBase extends FormBase implements BaseFormIdInterface, Trus
    *
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
    *   The entity type manager.
-   * @param \Drupal\media_library\MediaLibraryUiBuilder $library_ui_builder
+   * @param \Drupal\media_library\MediaLibraryUiBuilderInterface $library_ui_builder
    *   The media library UI builder.
    * @param \Drupal\media_library\OpenerResolverInterface $opener_resolver
    *   The opener resolver.
    */
-  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilder $library_ui_builder, OpenerResolverInterface $opener_resolver) {
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilderInterface $library_ui_builder, OpenerResolverInterface $opener_resolver) {
     $this->entityTypeManager = $entity_type_manager;
     $this->libraryUiBuilder = $library_ui_builder;
     $this->viewBuilder = $this->entityTypeManager->getViewBuilder('media');
diff --git a/core/modules/media_library/src/Form/FileUploadForm.php b/core/modules/media_library/src/Form/FileUploadForm.php
index 2afbb0ae57..f7e0322575 100644
--- a/core/modules/media_library/src/Form/FileUploadForm.php
+++ b/core/modules/media_library/src/Form/FileUploadForm.php
@@ -20,7 +20,7 @@
 use Drupal\file\Plugin\Field\FieldType\FileItem;
 use Drupal\media\MediaInterface;
 use Drupal\media\MediaTypeInterface;
-use Drupal\media_library\MediaLibraryUiBuilder;
+use Drupal\media_library\MediaLibraryUiBuilderInterface;
 use Drupal\media_library\OpenerResolverInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;

@@ -72,7 +70,7 @@ class FileUploadForm extends AddFormBase {
    *
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
    *   The entity type manager.
-   * @param \Drupal\media_library\MediaLibraryUiBuilder $library_ui_builder
+   * @param \Drupal\media_library\MediaLibraryUiBuilderInterface $library_ui_builder
    *   The media library UI builder.
    * @param \Drupal\Core\Render\ElementInfoManagerInterface $element_info
    *   The element info manager.
@@ -87,7 +85,7 @@ class FileUploadForm extends AddFormBase {
    * @param \Drupal\file\FileRepositoryInterface $file_repository
    *   The file repository service.
    */
-  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilder $library_ui_builder, ElementInfoManagerInterface $element_info, RendererInterface $renderer, FileSystemInterface $file_system, OpenerResolverInterface $opener_resolver, FileUsageInterface $file_usage, FileRepositoryInterface $file_repository) {
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilderInterface $library_ui_builder, ElementInfoManagerInterface $element_info, RendererInterface $renderer, FileSystemInterface $file_system, OpenerResolverInterface $opener_resolver, FileUsageInterface $file_usage, FileRepositoryInterface $file_repository) {
     parent::__construct($entity_type_manager, $library_ui_builder, $opener_resolver);
     $this->elementInfo = $element_info;
     $this->renderer = $renderer;
diff --git a/core/modules/media_library/src/Form/OEmbedForm.php b/core/modules/media_library/src/Form/OEmbedForm.php
index 8b70c89691..3a52c7f4b1 100644
--- a/core/modules/media_library/src/Form/OEmbedForm.php
+++ b/core/modules/media_library/src/Form/OEmbedForm.php
@@ -10,7 +10,7 @@
 use Drupal\media\OEmbed\ResourceFetcherInterface;
 use Drupal\media\OEmbed\UrlResolverInterface;
 use Drupal\media\Plugin\media\Source\OEmbedInterface;
-use Drupal\media_library\MediaLibraryUiBuilder;
+use Drupal\media_library\MediaLibraryUiBuilderInterface;
 use Drupal\media_library\OpenerResolverInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;

@@ -41,7 +41,7 @@ class OEmbedForm extends AddFormBase {
    *
    * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
    *   The entity type manager.
-   * @param \Drupal\media_library\MediaLibraryUiBuilder $library_ui_builder
+   * @param \Drupal\media_library\MediaLibraryUiBuilderInterface $library_ui_builder
    *   The media library UI builder.
    * @param \Drupal\media\OEmbed\UrlResolverInterface $url_resolver
    *   The oEmbed URL resolver service.
@@ -50,7 +50,7 @@ class OEmbedForm extends AddFormBase {
    * @param \Drupal\media_library\OpenerResolverInterface $opener_resolver
    *   The opener resolver.
    */
-  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilder $library_ui_builder, UrlResolverInterface $url_resolver, ResourceFetcherInterface $resource_fetcher, OpenerResolverInterface $opener_resolver = NULL) {
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, MediaLibraryUiBuilderInterface $library_ui_builder, UrlResolverInterface $url_resolver, ResourceFetcherInterface $resource_fetcher, OpenerResolverInterface $opener_resolver = NULL) {
     parent::__construct($entity_type_manager, $library_ui_builder, $opener_resolver);
     $this->urlResolver = $url_resolver;
     $this->resourceFetcher = $resource_fetcher;
diff --git a/core/modules/media_library/src/MediaLibraryUiBuilder.php b/core/modules/media_library/src/MediaLibraryUiBuilder.php
index 47143fcc25..be7c293365 100644
--- a/core/modules/media_library/src/MediaLibraryUiBuilder.php
+++ b/core/modules/media_library/src/MediaLibraryUiBuilder.php
@@ -3,6 +3,7 @@
 namespace Drupal\media_library;

 use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Access\AccessResultInterface;
 use Drupal\Core\Form\FormBuilderInterface;
 use Drupal\Core\Form\FormState;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
@@ -20,7 +21,7 @@
  *   This service is an internal part of the modal media library dialog and
  *   does not provide any extension points.
  */
-class MediaLibraryUiBuilder {
+class MediaLibraryUiBuilder implements MediaLibraryUiBuilderInterface {

   use StringTranslationTrait;

@@ -82,12 +83,9 @@ public function __construct(EntityTypeManagerInterface $entity_type_manager, Req
   }

   /**
-   * Get media library dialog options.
-   *
-   * @return array
-   *   The media library dialog options.
+   * {@inheritDoc}
    */
-  public static function dialogOptions() {
+  public static function dialogOptions(): array {
     return [
       'dialogClass' => 'media-library-widget-modal',
       'title' => t('Add or select media'),
@@ -97,16 +95,9 @@ public static function dialogOptions() {
   }

   /**
-   * Build the media library UI.
-   *
-   * @param \Drupal\media_library\MediaLibraryState $state
-   *   (optional) The current state of the media library, derived from the
-   *   current request.
-   *
-   * @return array
-   *   The render array for the media library.
+   * {@inheritDoc}
    */
-  public function buildUi(MediaLibraryState $state = NULL) {
+  public function buildUi(MediaLibraryState $state = NULL): array {
     if (!$state) {
       $state = MediaLibraryState::fromRequest($this->request);
     }
@@ -163,18 +154,9 @@ protected function buildLibraryContent(MediaLibraryState $state) {
   }

   /**
-   * Check access to the media library.
-   *
-   * @param \Drupal\Core\Session\AccountInterface $account
-   *   Run access checks for this account.
-   * @param \Drupal\media_library\MediaLibraryState $state
-   *   (optional) The current state of the media library, derived from the
-   *   current request.
-   *
-   * @return \Drupal\Core\Access\AccessResult
-   *   The access result.
+   * {@inheritdoc}
    */
-  public function checkAccess(AccountInterface $account, MediaLibraryState $state = NULL) {
+  public function checkAccess(AccountInterface $account, MediaLibraryState $state = NULL): AccessResultInterface {
     if (!$state) {
       try {
         $state = MediaLibraryState::fromRequest($this->request);
diff --git a/core/modules/media_library/src/MediaLibraryUiBuilderInterface.php b/core/modules/media_library/src/MediaLibraryUiBuilderInterface.php
new file mode 100644
index 0000000000..bd07945baf
--- /dev/null
+++ b/core/modules/media_library/src/MediaLibraryUiBuilderInterface.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\media_library;
+
+use Drupal\Core\Access\AccessResultInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Defines an interface for media library UI builder.
+ */
+interface MediaLibraryUiBuilderInterface {
+
+  /**
+   * Get media library dialog options.
+   *
+   * @return array
+   *   The media library dialog options.
+   */
+  public static function dialogOptions(): array;
+
+  /**
+   * Build the media library UI.
+   *
+   * @param \Drupal\media_library\MediaLibraryState|null $state
+   *   (optional) The current state of the media library, derived from the
+   *   current request.
+   *
+   * @return array
+   *   The render array for the media library.
+   */
+  public function buildUi(MediaLibraryState $state = NULL): array;
+
+  /**
+   * Check access to the media library.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   Run access checks for this account.
+   * @param \Drupal\media_library\MediaLibraryState|null $state
+   *   (optional) The current state of the media library, derived from the
+   *   current request.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function checkAccess(AccountInterface $account, MediaLibraryState $state = NULL): AccessResultInterface;
+
+}