diff --git a/amp.services.yml b/amp.services.yml
index bd32d3e..ebb503f 100644
--- a/amp.services.yml
+++ b/amp.services.yml
@@ -27,7 +27,7 @@ services:
     class: Drupal\amp\Service\AMPService
     arguments: []
   amp.query_parameters:
-    class: Drupal\amp\Utility\AmpQueryParamaters
+    class: Drupal\amp\Utility\AmpQueryParameters
   amp.merge_metadata:
     class: Drupal\amp\Utility\AmpMergeMetadata
     arguments: ['@entity_type.manager']
diff --git a/src/AmpPrepareMetadataJsonInterface.php b/src/AmpPrepareMetadataJsonInterface.php
new file mode 100644
index 0000000..f273ef6
--- /dev/null
+++ b/src/AmpPrepareMetadataJsonInterface.php
@@ -0,0 +1,48 @@
+<?php
+
+namespace Drupal\amp;
+
+use Drupal\node\NodeInterface;
+
+/**
+ * Provides an interface for preparing AMP Metadata JSON.
+ */
+interface AmpPrepareMetadataJsonInterface {
+
+  /**
+   * Gets the encoded AMP metadata JSON.
+   *
+   * @param array $amp_metadata_settings
+   *   The array containing AMP metadata settings.
+   * @param string $canonical_url
+   *   The canonical url for this node.
+   * @param NodeInterface $node
+   *   The node object.
+   *
+   * @return string
+   *   A JSON encoded string on success or FALSE on failure.
+   */
+  public function getJson(array $amp_metadata_settings, $canonical_url, NodeInterface $node);
+
+  /**
+   * Gets the array containing metadata ready to be converted to JSON.
+   */
+  public function getPreparedMetadataJson();
+
+  /**
+   * Allows additions or changes to metadata ready to be converted to JSON.
+   *
+   * @param array $prepared_metadata
+   */
+  public function setPreparedMetadataJson($prepared_metadata);
+
+  /**
+   * Get the list of metadata items.
+   */
+  public function getAmpMetadataList();
+
+  /**
+   * Sets the list of metadata items.
+   */
+  public function setAmpMetadataList();
+}
diff --git a/src/Utility/AmpPrepareMetadataJson.php b/src/Utility/AmpPrepareMetadataJson.php
index 72b00e5..7cb99e1 100644
--- a/src/Utility/AmpPrepareMetadataJson.php
+++ b/src/Utility/AmpPrepareMetadataJson.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\amp\Utility;
 
+use Drupal\amp\AmpPrepareMetadataJsonInterface;
 use Drupal\Component\Render\PlainTextOutput;
 use Drupal\Core\Image\ImageInterface;
 use Drupal\Core\StreamWrapper\PublicStream;
@@ -19,7 +20,7 @@ use Drupal\node\NodeInterface;
  *
  * @package Drupal\amp\Utility
  */
-class AmpPrepareMetadataJson {
+class AmpPrepareMetadataJson implements AmpPrepareMetadataJsonInterface {
 
   /**
    * The array containing AMP metadata settings
@@ -84,17 +85,7 @@ class AmpPrepareMetadataJson {
   }
 
   /**
-   * Gets the encoded AMP metadata JSON.
-   *
-   * @param array $amp_metadata_settings
-   *   The array containing AMP metadata settings.
-   * @param string $canonical_url
-   *   The canonical url for this node.
-   * @param NodeInterface $node
-   *   The node object.
-   *
-   * @return string
-   *   A JSON encoded string on success or FALSE on failure.
+   * {@inheritdoc}
    */
   public function getJson(array $amp_metadata_settings, $canonical_url, NodeInterface $node) {
     $this->ampMetadataSettings = $amp_metadata_settings;
@@ -118,20 +109,19 @@ class AmpPrepareMetadataJson {
   }
 
   /**
-   * Gets the array containing metadata ready to be converted to JSON.
+   * {@inheritdoc}
    */
   public function getPreparedMetadataJson() {
     return $this->ampPreparedMetadataJson;
   }
 
   /**
-   * Allows additions or changes to metadata ready to be converted to JSON.
-   *
-   * @param array $prepared_metadata
+   * {@inheritdoc}
    */
   public function setPreparedMetadataJson($prepared_metadata) {
     $this->ampPreparedMetadataJson = $prepared_metadata;
   }
+
   /**
    * Prepares a metadata array to be ready for JSON conversion.
    */
@@ -380,14 +370,14 @@ class AmpPrepareMetadataJson {
   }
 
   /**
-   * Get the list of metadata items.
+   * {@inheritdoc}
    */
   public function getAmpMetadataList() {
     return $this->ampMetadataList;
   }
 
   /**
-   * Sets the list of metadata items.
+   * {@inheritdoc}
    */
   public function setAmpMetadataList() {
     $this->ampMetadataList = [