diff --git a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
index 50c7e1c..d3779eb 100644
--- a/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
+++ b/core/modules/rest/src/Plugin/rest/resource/EntityResourceValidationTrait.php
@@ -2,11 +2,9 @@
 
 namespace Drupal\rest\Plugin\rest\resource;
 
-use Drupal\Component\Render\PlainTextOutput;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
-use Drupal\rest\Exception\EntityValidationException;
-use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
+use Drupal\serialization\Exception\EntityValidationException;
 
 /**
  * @internal
@@ -20,7 +18,7 @@
    * @param \Drupal\Core\Entity\EntityInterface $entity
    *   The entity to validate.
    *
-   * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException
+   * @throws \Drupal\serialization\Exception\EntityValidationException
    *   If validation errors are found.
    */
   protected function validate(EntityInterface $entity) {
@@ -35,7 +33,7 @@ protected function validate(EntityInterface $entity) {
     $violations->filterByFieldAccess();
 
     if ($violations->count() > 0) {
-      throw new EntityValidationException($violations);
+      throw new EntityValidationException($violations, 'Validation of the {$entity->getEntityTypeId()} entity failed');
     }
   }
 
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index ebb03e2..82ed3a9 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -683,7 +683,15 @@ public function testPost() {
     $response = $this->request('POST', $url, $request_options);
     $label_field = $this->entity->getEntityType()->hasKey('label') ? $this->entity->getEntityType()->getKey('label') : static::$labelFieldName;
     $label_field_capitalized = ucfirst($label_field);
-    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\n$label_field: $label_field_capitalized: this field cannot hold more than 1 values.\n", $response);
+
+    $entity_type_id = static::$entityTypeId;
+    $error = [
+      'message' => "Validation of the $entity_type_id entity failed",
+      'errors' => [
+        $label_field => "$label_field_capitalized: this field cannot hold more than 1 values.",
+      ],
+    ];
+    $this->assertResourceErrorResponse(422, json_encode($error), $response);
 
 
     $request_options[RequestOptions::BODY] = $parseable_invalid_request_body_2;
@@ -691,7 +699,13 @@ public function testPost() {
 
     // DX: 422 when invalid entity: UUID field too long.
     $response = $this->request('POST', $url, $request_options);
-    $this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nuuid.0.value: UUID: may not be longer than 128 characters.\n", $response);
+    $error = [
+      'message' => "Validation of the $entity_type_id entity failed",
+      'errors' => [
+        'uuid.0.value' => 'UUID: may not be longer than 128 characters.',
+      ],
+    ];
+    $this->assertResourceErrorResponse(422, json_encode($error), $response);
 
 
     $request_options[RequestOptions::BODY] = $parseable_invalid_request_body_3;
diff --git a/core/modules/serialization/serialization.services.yml b/core/modules/serialization/serialization.services.yml
index 3e47b00..3d74e19 100644
--- a/core/modules/serialization/serialization.services.yml
+++ b/core/modules/serialization/serialization.services.yml
@@ -64,6 +64,10 @@ services:
     class: Drupal\serialization\Normalizer\TypedDataNormalizer
     tags:
       - { name: normalizer }
+  serializer.normalizer.entity_validation_exception:
+    class: \Drupal\serialization\Normalizer\EntityValidationExceptionNormalizer
+    tags:
+      - { name: normalizer }
   serializer.encoder.json:
     class: Drupal\serialization\Encoder\JsonEncoder
     tags:
diff --git a/core/modules/serialization/src/EventSubscriber/DefaultExceptionSubscriber.php b/core/modules/serialization/src/EventSubscriber/DefaultExceptionSubscriber.php
index a1e7bad..5be6c33 100644
--- a/core/modules/serialization/src/EventSubscriber/DefaultExceptionSubscriber.php
+++ b/core/modules/serialization/src/EventSubscriber/DefaultExceptionSubscriber.php
@@ -62,13 +62,18 @@ protected static function getPriority() {
    *   The event to process.
    */
   public function on4xx(GetResponseForExceptionEvent $event) {
-    /** @var \Symfony\Component\HttpKernel\Exception\HttpExceptionInterface $exception */
+    /** @var \Symfony\Component\HttpKernel\Exception\HttpExceptionInterface|\Exception $exception */
     $exception = $event->getException();
     $request = $event->getRequest();
 
     $format = $request->getRequestFormat();
-    $content = ['message' => $event->getException()->getMessage()];
-    $encoded_content = $this->serializer->serialize($content, $format);
+
+    if ($this->serializer->supportsNormalization($exception, $format)) {
+      $encoded_content = $this->serializer->serialize($exception, $format);
+    }
+    else {
+      $encoded_content = ['message' => $exception->getMessage()];
+    }
     $headers = $exception->getHeaders();
 
     // Add the MIME type from the request to send back in the header.
diff --git a/core/modules/rest/src/Exception/EntityValidationException.php b/core/modules/serialization/src/Exception/EntityValidationException.php
similarity index 73%
rename from core/modules/rest/src/Exception/EntityValidationException.php
rename to core/modules/serialization/src/Exception/EntityValidationException.php
index b0b2255..caf5de7 100644
--- a/core/modules/rest/src/Exception/EntityValidationException.php
+++ b/core/modules/serialization/src/Exception/EntityValidationException.php
@@ -1,10 +1,18 @@
 <?php
 
-namespace Drupal\rest\Exception;
+namespace Drupal\serialization\Exception;
 
 use Drupal\Core\Entity\EntityConstraintViolationListInterface;
 use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
 
+/**
+ * An exception thrown when entity validation failed.
+ *
+ * This exception is normalized/encoded into a nice machine readable error
+ * message.
+ *
+ * @see \Drupal\serialization\Normalizer\EntityValidationExceptionNormalizer
+ */
 class EntityValidationException extends UnprocessableEntityHttpException {
 
   /**
diff --git a/core/modules/rest/src/Normalizer/EntityValidationExceptionNormalizer.php b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
similarity index 63%
rename from core/modules/rest/src/Normalizer/EntityValidationExceptionNormalizer.php
rename to core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
index 023f0ec..0fccf30 100644
--- a/core/modules/rest/src/Normalizer/EntityValidationExceptionNormalizer.php
+++ b/core/modules/serialization/src/Normalizer/EntityValidationExceptionNormalizer.php
@@ -1,13 +1,14 @@
 <?php
 
-namespace Drupal\rest\Normalizer;
+namespace Drupal\serialization\Normalizer;
 
 use Drupal\Component\Render\PlainTextOutput;
-use Drupal\rest\Exception\EntityValidationException;
-use Drupal\serialization\Normalizer\NormalizerBase;
-use Symfony\Component\Serializer\Normalizer\scalar;
+use Drupal\serialization\Exception\EntityValidationException;
 use Symfony\Component\Validator\ConstraintViolation;
 
+/**
+ * Normalizes entity validation errors.
+ */
 class EntityValidationExceptionNormalizer extends NormalizerBase {
 
   /**
@@ -18,16 +19,20 @@ class EntityValidationExceptionNormalizer extends NormalizerBase {
   /**
    * {@inheritdoc}
    */
-  public function normalize($object, $format = NULL, array $context = array()) {
+  public function normalize($object, $format = NULL, array $context = []) {
     $result = [];
     if ($object instanceof EntityValidationException) {
       $violations = $object->getViolations();
+      $result['message'] = $object->getMessage();
 
-      $result = array_reduce(iterator_to_array($violations), function (array $carry, ConstraintViolation $violation) {
+      // Group violations by field path.
+      $result['errors'] = array_reduce(iterator_to_array($violations), function (array $carry, ConstraintViolation $violation) {
         $carry[$violation->getPropertyPath()][] = PlainTextOutput::renderFromHtml($violation->getMessage());
         return $carry;
       }, []);
+
     }
+
     return $result;
   }
 
diff --git a/core/tests/README.md b/core/tests/README.md
index 566fa23..a454c7e 100644
--- a/core/tests/README.md
+++ b/core/tests/README.md
@@ -1,4 +1,4 @@
-# Running tests
+# Runnin testt
 
 ## Functional tests