diff --git a/collabora_online.services.yml b/collabora_online.services.yml
index b548f9b3..a630a6ac 100644
--- a/collabora_online.services.yml
+++ b/collabora_online.services.yml
@@ -4,5 +4,7 @@ services:
   logger.channel.collabora_online:
     parent: logger.channel_base
     arguments: ['cool']
-  Drupal\collabora_online\Cool\CollaboraDiscoveryFetcher: { }
-  Drupal\collabora_online\Cool\CollaboraDiscovery: { }
+  Drupal\collabora_online\Cool\CollaboraDiscoveryFetcherInterface:
+    class: Drupal\collabora_online\Cool\CollaboraDiscoveryFetcher
+  Drupal\collabora_online\Cool\CollaboraDiscoveryInterface:
+    class: Drupal\collabora_online\Cool\CollaboraDiscovery
diff --git a/src/Controller/ViewerController.php b/src/Controller/ViewerController.php
index acee9ab8..fd43cec7 100644
--- a/src/Controller/ViewerController.php
+++ b/src/Controller/ViewerController.php
@@ -14,7 +14,7 @@
 
 namespace Drupal\collabora_online\Controller;
 
-use Drupal\collabora_online\Cool\CollaboraDiscovery;
+use Drupal\collabora_online\Cool\CollaboraDiscoveryInterface;
 use Drupal\collabora_online\Cool\CoolUtils;
 use Drupal\collabora_online\Exception\CollaboraNotAvailableException;
 use Drupal\Core\Controller\ControllerBase;
@@ -32,13 +32,13 @@ class ViewerController extends ControllerBase {
   /**
    * The controller constructor.
    *
-   * @param \Drupal\collabora_online\Cool\CollaboraDiscovery $discovery
+   * @param \Drupal\collabora_online\Cool\CollaboraDiscoveryInterface $discovery
    *   Service to fetch a WOPI client URL.
    * @param \Drupal\Core\Render\RendererInterface $renderer
    *   The renderer service.
    */
   public function __construct(
-    protected readonly CollaboraDiscovery $discovery,
+    protected readonly CollaboraDiscoveryInterface $discovery,
     protected readonly RendererInterface $renderer,
   ) {}
 
diff --git a/src/Cool/CollaboraDiscovery.php b/src/Cool/CollaboraDiscovery.php
index 2f761e4d..e11adb2e 100644
--- a/src/Cool/CollaboraDiscovery.php
+++ b/src/Cool/CollaboraDiscovery.php
@@ -19,30 +19,20 @@
 /**
  * Service to get a WOPI client url for a given MIME type.
  */
-class CollaboraDiscovery {
+class CollaboraDiscovery implements CollaboraDiscoveryInterface {
 
   /**
    * Constructor.
    *
-   * @param \Drupal\collabora_online\Cool\CollaboraDiscoveryFetcher $discoveryFetcher
+   * @param \Drupal\collabora_online\Cool\CollaboraDiscoveryFetcherInterface $discoveryFetcher
    *   Service to load the discovery.xml from the Collabora server.
    */
   public function __construct(
-    protected readonly CollaboraDiscoveryFetcher $discoveryFetcher,
+    protected readonly CollaboraDiscoveryFetcherInterface $discoveryFetcher,
   ) {}
 
   /**
-   * Gets the URL for the WOPI client.
-   *
-   * @param string $mimetype
-   *   Mime type for which to get the WOPI client url.
-   *   This refers to config entries in the discovery.xml file.
-   *
-   * @return string
-   *   The WOPI client url.
-   *
-   * @throws \Drupal\collabora_online\Exception\CollaboraNotAvailableException
-   *   The client url cannot be retrieved.
+   * {@inheritdoc}
    */
   public function getWopiClientURL(string $mimetype = 'text/plain'): string {
     $xml = $this->discoveryFetcher->getDiscoveryXml();
diff --git a/src/Cool/CollaboraDiscoveryFetcher.php b/src/Cool/CollaboraDiscoveryFetcher.php
index 600893ef..290647b2 100644
--- a/src/Cool/CollaboraDiscoveryFetcher.php
+++ b/src/Cool/CollaboraDiscoveryFetcher.php
@@ -25,7 +25,7 @@
 /**
  * Service to load the discovery.xml from the Collabora server.
  */
-class CollaboraDiscoveryFetcher {
+class CollaboraDiscoveryFetcher implements CollaboraDiscoveryFetcherInterface {
 
   /**
    * Constructor.
@@ -45,13 +45,7 @@ public function __construct(
   ) {}
 
   /**
-   * Gets the contents of discovery.xml from the Collabora server.
-   *
-   * @return string
-   *   The full contents of discovery.xml.
-   *
-   * @throws \Drupal\collabora_online\Exception\CollaboraNotAvailableException
-   *   The client url cannot be retrieved.
+   * {@inheritdoc}
    */
   public function getDiscoveryXml(): string {
     $discovery_url = $this->getWopiClientServerBaseUrl() . '/hosting/discovery';
diff --git a/src/Cool/CollaboraDiscoveryFetcherInterface.php b/src/Cool/CollaboraDiscoveryFetcherInterface.php
new file mode 100644
index 00000000..726663dd
--- /dev/null
+++ b/src/Cool/CollaboraDiscoveryFetcherInterface.php
@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * Copyright the Collabora Online contributors.
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\collabora_online\Cool;
+
+/**
+ * Service to load the discovery.xml from the Collabora server.
+ */
+interface CollaboraDiscoveryFetcherInterface {
+
+  /**
+   * Gets the contents of discovery.xml from the Collabora server.
+   *
+   * @return string
+   *   The full contents of discovery.xml.
+   *
+   * @throws \Drupal\collabora_online\Exception\CollaboraNotAvailableException
+   *   The client url cannot be retrieved.
+   */
+  public function getDiscoveryXml(): string;
+
+}
diff --git a/src/Cool/CollaboraDiscoveryInterface.php b/src/Cool/CollaboraDiscoveryInterface.php
new file mode 100644
index 00000000..b8aae932
--- /dev/null
+++ b/src/Cool/CollaboraDiscoveryInterface.php
@@ -0,0 +1,37 @@
+<?php
+
+/*
+ * Copyright the Collabora Online contributors.
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\collabora_online\Cool;
+
+/**
+ * Service to get a WOPI client url for a given MIME type.
+ */
+interface CollaboraDiscoveryInterface {
+
+  /**
+   * Gets the URL for the WOPI client.
+   *
+   * @param string $mimetype
+   *   Mime type for which to get the WOPI client url.
+   *   This refers to config entries in the discovery.xml file.
+   *
+   * @return string
+   *   The WOPI client url.
+   *
+   * @throws \Drupal\collabora_online\Exception\CollaboraNotAvailableException
+   *   The client url cannot be retrieved.
+   */
+  public function getWopiClientURL(string $mimetype = 'text/plain'): string;
+
+}
diff --git a/tests/src/ExistingSite/FetchClientUrlTest.php b/tests/src/ExistingSite/FetchClientUrlTest.php
index 9d1f04cb..c4f8ff61 100644
--- a/tests/src/ExistingSite/FetchClientUrlTest.php
+++ b/tests/src/ExistingSite/FetchClientUrlTest.php
@@ -14,7 +14,7 @@
 
 namespace Drupal\Tests\collabora_online\ExistingSite;
 
-use Drupal\collabora_online\Cool\CollaboraDiscovery;
+use Drupal\collabora_online\Cool\CollaboraDiscoveryInterface;
 use Drupal\collabora_online\Exception\CollaboraNotAvailableException;
 use weitzman\DrupalTestTraits\ExistingSiteBase;
 
@@ -27,8 +27,8 @@ class FetchClientUrlTest extends ExistingSiteBase {
    * Tests fetching the client url.
    */
   public function testFetchClientUrl(): void {
-    /** @var \Drupal\collabora_online\Cool\CollaboraDiscovery $discovery */
-    $discovery = \Drupal::service(CollaboraDiscovery::class);
+    /** @var \Drupal\collabora_online\Cool\CollaboraDiscoveryInterface $discovery */
+    $discovery = \Drupal::service(CollaboraDiscoveryInterface::class);
     $client_url = $discovery->getWopiClientURL();
     // The protocol, domain and port are known when this test runs in the
     // docker-compose setup.
@@ -46,8 +46,8 @@ public function testFetchClientUrlWithMisconfiguration(): void {
           'server' => 'httx://example.com',
         ],
       ]);
-    /** @var \Drupal\collabora_online\Cool\CollaboraDiscovery $discovery */
-    $discovery = \Drupal::service(CollaboraDiscovery::class);
+    /** @var \Drupal\collabora_online\Cool\CollaboraDiscoveryInterface $discovery */
+    $discovery = \Drupal::service(CollaboraDiscoveryInterface::class);
 
     $this->expectException(CollaboraNotAvailableException::class);
     $this->expectExceptionMessage("The configured Collabora Online server address must begin with 'http://' or 'https://'. Found 'httx://example.com'.");