diff --git a/assets/js/app/ajax-save.js b/assets/js/app/ajax-save.js
index d19fa8177..5f53abc51 100644
--- a/assets/js/app/ajax-save.js
+++ b/assets/js/app/ajax-save.js
@@ -46,7 +46,8 @@ $(document).ready(function() {
         $('#toastTitle').addClass(['toast-header', typeClass]);
         $('#toastNotification').append(notification);
         $('#toastType').append(toastType);
-        $('#toastBody').append(toastMessage);
+        // Set as text, because validation messages can contain the value that was rejected.
+        $('#toastBody').text(toastMessage);
 
         $(document).ready(function() {
             let toastElList = [].slice.call(document.querySelectorAll('.toast'));
@@ -59,6 +60,27 @@ $(document).ready(function() {
             });
         });
     }
+
+    // Shows the validation errors of a rejected save above the form, the way the classic
+    // (non-ajax) save shows them, see `templates/content/edit.html.twig`.
+    function showValidationErrors(errors) {
+        let container = $('<div id="editcontent-validation-errors"></div>');
+
+        errors.forEach(function(error) {
+            let alert = $('<div class="alert alert-danger" role="alert"></div>');
+            alert.text(error.property ? error.property + ': ' + error.message : error.message);
+            container.append(alert);
+        });
+
+        clearValidationErrors();
+        $(form).before(container);
+        container[0].scrollIntoView({ block: 'nearest' });
+    }
+
+    function clearValidationErrors() {
+        $('#editcontent-validation-errors').remove();
+    }
+
     this.href = window.location.pathname;
 
     let duplicate_id = this.href.substring(this.href.lastIndexOf('/') + 1);
@@ -86,6 +108,7 @@ $(document).ready(function() {
                 elementButton.prop('disabled', false);
             },
             success: function(data, textStatus) {
+                clearValidationErrors();
                 if (!record_id) {
                     window.location.replace(data.url);
                 } else if (window.location.pathname === '/bolt/duplicate/' + duplicate_id) {
@@ -99,6 +122,21 @@ $(document).ready(function() {
                 }
             },
             error: function(jq, status, err) {
+                let response = jq.responseJSON;
+
+                // The save was rejected by the content validator, which returns its
+                // violations as JSON, so we can show the validator's own messages.
+                if (jq.status === 422 && response && Array.isArray(response.errors)) {
+                    let messages = response.errors.map(function(error) {
+                        return error.message;
+                    });
+
+                    showValidationErrors(response.errors);
+                    showToast(response.type, messages.join(' '), response.status, response.notification, dom_element);
+
+                    return;
+                }
+
                 // eslint-disable-next-line no-console
                 console.log(status, err);
                 showToast();
diff --git a/src/Controller/Backend/ContentEditController.php b/src/Controller/Backend/ContentEditController.php
index 204f8927f..d932683dc 100644
--- a/src/Controller/Backend/ContentEditController.php
+++ b/src/Controller/Backend/ContentEditController.php
@@ -42,6 +42,7 @@
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 use Symfony\Component\Routing\Attribute\Route;
 use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
+use Symfony\Component\Validator\ConstraintViolationListInterface;
 use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
 use Symfony\Contracts\Translation\TranslatorInterface;
 
@@ -153,6 +154,13 @@ public function save(Request $request, ?Content $originalContent = null, ?Conten
         if ($enableContentValidator && $contentValidator) {
             $constraintViolations = $contentValidator->validate($content);
             if (count($constraintViolations) > 0) {
+                // When "Saving Ajaxy" the editor isn't re-rendered, so the violations that
+                // renderEditor() puts in the HTML would never reach the browser. Return them
+                // as JSON instead, for `assets/js/app/ajax-save.js` to display.
+                if ($request->isXmlHttpRequest()) {
+                    return $this->renderValidationErrors($request, $constraintViolations);
+                }
+
                 $this->addFlash('danger', 'content.validation_errors');
 
                 return $this->renderEditor($request, $content, $constraintViolations);
@@ -651,4 +659,27 @@ private function renderEditor(Request $request, Content $content, $errors = null
 
         return $this->render('@bolt/content/edit.html.twig', $twigvars);
     }
+
+    private function renderValidationErrors(Request $request, ConstraintViolationListInterface $constraintViolations): JsonResponse
+    {
+        $locale = $request->getLocale();
+
+        $errors = [];
+        foreach ($constraintViolations as $constraintViolation) {
+            $errors[] = [
+                'property' => $constraintViolation->getPropertyPath(),
+                'message' => (string) $constraintViolation->getMessage(),
+            ];
+        }
+
+        return new JsonResponse(
+            [
+                'status' => 'danger',
+                'type' => $this->translator->trans('warning', [], null, $locale),
+                'notification' => $this->translator->trans('flash_messages.notification', [], null, $locale),
+                'errors' => $errors,
+            ],
+            Response::HTTP_UNPROCESSABLE_ENTITY
+        );
+    }
 }
diff --git a/tests/php/Controller/Backend/ContentEditControllerSaveTest.php b/tests/php/Controller/Backend/ContentEditControllerSaveTest.php
new file mode 100644
index 000000000..ae88a3d6f
--- /dev/null
+++ b/tests/php/Controller/Backend/ContentEditControllerSaveTest.php
@@ -0,0 +1,142 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Bolt\Tests\Controller\Backend;
+
+use Bolt\Configuration\Config;
+use Bolt\Controller\Backend\ContentEditController;
+use Bolt\Controller\TwigAwareController;
+use Bolt\Entity\Content;
+use Bolt\Enum\Statuses;
+use Bolt\Event\Listener\ContentFillListener;
+use Bolt\Repository\ContentRepository;
+use Bolt\Repository\MediaRepository;
+use Bolt\Repository\RelationRepository;
+use Bolt\Repository\TaxonomyRepository;
+use Bolt\Utils\ContentHelper;
+use Bolt\Validator\ContentValidatorInterface;
+use Doctrine\ORM\EntityManagerInterface;
+use PHPUnit\Framework\TestCase;
+use ReflectionProperty;
+use Symfony\Component\DependencyInjection\Container;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
+use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorageInterface;
+use Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface;
+use Symfony\Component\Security\Csrf\CsrfTokenManagerInterface;
+use Symfony\Component\Validator\ConstraintViolation;
+use Symfony\Component\Validator\ConstraintViolationList;
+use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
+
+class ContentEditControllerSaveTest extends TestCase
+{
+    /**
+     * A save over ajax that the content validator rejects has to answer with the
+     * violations as JSON, because `assets/js/app/ajax-save.js` can do nothing with a
+     * re-rendered editor. This test fails if that response contract changes.
+     */
+    public function testAjaxSaveReturnsTheValidationViolationsAsJson(): void
+    {
+        $controller = $this->createController();
+
+        $response = $controller->save(
+            $this->ajaxSaveRequest(),
+            new Content(),
+            $this->contentValidatorRejectingWith(
+                new ConstraintViolation('End datetime is required', null, [], null, 'end_datetime', null),
+                // Validators built by hand often leave the property path empty.
+                new ConstraintViolation('The record is not valid', null, [], null, null, null)
+            )
+        );
+
+        self::assertInstanceOf(JsonResponse::class, $response);
+        self::assertSame(Response::HTTP_UNPROCESSABLE_ENTITY, $response->getStatusCode());
+
+        $payload = json_decode((string) $response->getContent(), true);
+
+        self::assertSame('danger', $payload['status']);
+        self::assertSame('warning', $payload['type']);
+        self::assertSame('flash_messages.notification', $payload['notification']);
+        self::assertSame([
+            ['property' => 'end_datetime', 'message' => 'End datetime is required'],
+            ['property' => '', 'message' => 'The record is not valid'],
+        ], $payload['errors']);
+    }
+
+    private function createController(): ContentEditController
+    {
+        $controller = new ContentEditController(
+            $this->createMock(TaxonomyRepository::class),
+            $this->createMock(RelationRepository::class),
+            $this->createMock(ContentRepository::class),
+            $this->createMock(MediaRepository::class),
+            $this->createMock(EntityManagerInterface::class),
+            $this->createMock(UrlGeneratorInterface::class),
+            $this->createMock(ContentFillListener::class),
+            $this->createMock(EventDispatcherInterface::class),
+            'en',
+            $this->translatorReturningKeys(),
+            $this->createMock(ContentHelper::class)
+        );
+
+        $csrfTokenManager = $this->createMock(CsrfTokenManagerInterface::class);
+        $csrfTokenManager->method('isTokenValid')->willReturn(true);
+        $controller->setCsrfTokenManager($csrfTokenManager);
+
+        $authorizationChecker = $this->createMock(AuthorizationCheckerInterface::class);
+        $authorizationChecker->method('isGranted')->willReturn(true);
+
+        $container = new Container();
+        $container->set('security.authorization_checker', $authorizationChecker);
+        $container->set('security.token_storage', $this->createMock(TokenStorageInterface::class));
+        $controller->setContainer($container);
+
+        // Of the collaborators that `setAutowire()` injects, this code path only reads the
+        // config, so that is the only one set here.
+        (new ReflectionProperty(TwigAwareController::class, 'config'))->setValue($controller, $this->configWithValidatorEnabled());
+
+        return $controller;
+    }
+
+    private function configWithValidatorEnabled(): Config
+    {
+        $config = $this->createMock(Config::class);
+        $config->method('get')->willReturnCallback(
+            static fn (string $path, $default = null) => $path === 'general/validator_options/enable' ? true : $default
+        );
+
+        return $config;
+    }
+
+    private function translatorReturningKeys(): TranslatorInterface
+    {
+        $translator = $this->createMock(TranslatorInterface::class);
+        $translator->method('trans')->willReturnArgument(0);
+
+        return $translator;
+    }
+
+    private function contentValidatorRejectingWith(ConstraintViolation ...$violations): ContentValidatorInterface
+    {
+        $contentValidator = $this->createMock(ContentValidatorInterface::class);
+        $contentValidator->method('validate')->willReturn(new ConstraintViolationList($violations));
+
+        return $contentValidator;
+    }
+
+    private function ajaxSaveRequest(): Request
+    {
+        $request = Request::create('/bolt/edit/1', Request::METHOD_POST, [
+            '_csrf_token' => 'valid',
+            '_edit_locale' => 'en',
+            'status' => Statuses::DRAFT,
+        ]);
+        $request->headers->set('X-Requested-With', 'XMLHttpRequest');
+
+        return $request;
+    }
+}