diff --git a/CHANGELOG.md b/CHANGELOG.md
index e9c7c06..ca49197 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- [#174](https://github.com/itk-dev/devops_itksites/pull/174)
+  Show detection result errors and warnings as readable messages instead of
+  JSON, so long messages are no longer cut off
+
 ## [1.20.0] - 2026-11-04
 
 - [#172](https://github.com/itk-dev/devops_itksites/pull/172)
diff --git a/src/Controller/Admin/DetectionResultCrudController.php b/src/Controller/Admin/DetectionResultCrudController.php
index ba57bd0..dc085e8 100644
--- a/src/Controller/Admin/DetectionResultCrudController.php
+++ b/src/Controller/Admin/DetectionResultCrudController.php
@@ -55,12 +55,10 @@ public function configureFields(string $pageName): iterable
         yield DateTimeField::new('modifiedAt')->hideOnIndex();
         yield DateTimeField::new('lastContact');
         yield TextMonospaceField::new('harvesterVersion');
-        yield Field::new('prettyErrors')->onlyOnDetail()->setLabel('Errors')
-            ->setTemplatePath('EasyAdminBundle/Fields/code_highlight.html.twig')
-            ->setCustomOption('language', 'json');
-        yield Field::new('prettyWarnings')->onlyOnDetail()->setLabel('Warnings')
-            ->setTemplatePath('EasyAdminBundle/Fields/code_highlight.html.twig')
-            ->setCustomOption('language', 'json');
+        yield Field::new('errors')->onlyOnDetail()
+            ->setTemplatePath('EasyAdminBundle/Fields/harvester_messages.html.twig');
+        yield Field::new('warnings')->onlyOnDetail()
+            ->setTemplatePath('EasyAdminBundle/Fields/harvester_messages.html.twig');
         yield Field::new('prettyData')->onlyOnDetail()->setLabel('Data')
             ->setTemplatePath('EasyAdminBundle/Fields/code_highlight.html.twig')
             ->setCustomOption('language', 'json');
diff --git a/src/Entity/DetectionResult.php b/src/Entity/DetectionResult.php
index c9b5003..cae5cc5 100644
--- a/src/Entity/DetectionResult.php
+++ b/src/Entity/DetectionResult.php
@@ -219,16 +219,6 @@ public function setWarnings(array $warnings): self
         return $this;
     }
 
-    public function getPrettyErrors(): string
-    {
-        return json_encode($this->errors, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR);
-    }
-
-    public function getPrettyWarnings(): string
-    {
-        return json_encode($this->warnings, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR);
-    }
-
     public function getHash(): ?string
     {
         return $this->hash;
diff --git a/templates/EasyAdminBundle/Fields/harvester_messages.html.twig b/templates/EasyAdminBundle/Fields/harvester_messages.html.twig
new file mode 100644
index 0000000..eb24295
--- /dev/null
+++ b/templates/EasyAdminBundle/Fields/harvester_messages.html.twig
@@ -0,0 +1,22 @@
+{# @var field \EasyCorp\Bundle\EasyAdminBundle\Dto\FieldDto #}
+{# Errors or warnings from the harvester: a list of {source, message} with
+   optional container, command and exitCode. #}
+{% if field.value is empty %}
+    <span class="text-muted">None</span>
+{% else %}
+    <ul class="list-unstyled mb-0">
+        {% for item in field.value %}
+            <li class="mb-3">
+                <div>
+                    <strong>{{ item.source }}</strong>
+                    {%- if item.container is defined %} in {{ item.container }}{% endif %}
+                    {%- if item.exitCode is defined %} (exit {{ item.exitCode }}){% endif %}
+                </div>
+                {% if item.command is defined %}
+                    <code>{{ item.command }}</code>
+                {% endif %}
+                <pre class="mb-0" style="white-space: pre-wrap; overflow-wrap: anywhere">{{ item.message }}</pre>
+            </li>
+        {% endfor %}
+    </ul>
+{% endif %}
diff --git a/tests/Controller/Admin/AdminSmokeTest.php b/tests/Controller/Admin/AdminSmokeTest.php
index 0476086..45051fe 100644
--- a/tests/Controller/Admin/AdminSmokeTest.php
+++ b/tests/Controller/Admin/AdminSmokeTest.php
@@ -21,6 +21,7 @@
 use App\Controller\Admin\ServiceCertificateCrudController;
 use App\Controller\Admin\SiteCrudController;
 use App\Entity\Advisory;
+use App\Entity\DetectionResult;
 use App\Entity\Installation;
 use App\Entity\Module;
 use App\Entity\ModuleVersion;
@@ -193,6 +194,32 @@ public static function packageCrudControllerProvider(): iterable
         yield 'PackageVersion' => [PackageVersionCrudController::class, 3, 1];
     }
 
+    public function testDetectionResultDetailShowsErrorMessageInFull(): void
+    {
+        $client = static::createClient();
+        $entityManager = static::getContainer()->get('doctrine')->getManager();
+        $client->loginUser($entityManager->getRepository(User::class)->findOneBy([]));
+
+        $result = $entityManager->getRepository(DetectionResult::class)->findOneBy([]);
+        $message = "In CooldownPolicyConfig.php line 117:\n  bower-asset/jquery 4.0.0 has no published-time";
+        $result->setErrors([['source' => 'composer', 'message' => $message, 'container' => 'phpfpm', 'command' => 'composer outdated --all --format=json', 'exitCode' => 1]]);
+        $entityManager->flush();
+
+        $url = static::getContainer()->get(AdminUrlGenerator::class)
+            ->setController(DetectionResultCrudController::class)
+            ->setAction(Crud::PAGE_DETAIL)
+            ->setEntityId($result->getId())
+            ->generateUrl();
+
+        $client->request('GET', $url);
+
+        $this->assertResponseIsSuccessful();
+        // The message keeps its line breaks instead of showing a JSON-escaped "\n".
+        $this->assertSelectorTextContains('pre', 'has no published-time');
+        $this->assertStringContainsString($message, $client->getCrawler()->filter('pre')->text(null, false));
+        $this->assertSelectorTextContains('li code', 'composer outdated --all --format=json');
+    }
+
     public function testDockerImagesFilterByRegistry(): void
     {
         $client = static::createClient();