diff --git a/packages/vitec/Classes/Middleware/JsonCacheHeaders.php b/packages/vitec/Classes/Middleware/JsonCacheHeaders.php
new file mode 100644
index 0000000..4b0c5f7
--- /dev/null
+++ b/packages/vitec/Classes/Middleware/JsonCacheHeaders.php
@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Evomedien\Vitec\Middleware;
+
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\MiddlewareInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use TYPO3\CMS\Core\Http\Response;
+
+/**
+ * Normalizes client caching for the headless JSON API (/_json):
+ * a single "Cache-Control: no-cache" plus a content ETag, answering
+ * If-None-Match with an empty 304 so browsers revalidate instead of
+ * re-downloading (tickets 0011-FE / 0055-BE).
+ *
+ * "Expires: 0" is set on purpose: mod_expires leaves responses alone
+ * that already carry an Expires header, otherwise it would re-add
+ * max-age/Expires on top of ours (public/.htaccess ExpiresByType).
+ *
+ * Logged-in visitors (fe_typo_user cookie) keep TYPO3's own headers:
+ * their responses may be personalized and must not be eligible for
+ * shared revalidation.
+ */
+final class JsonCacheHeaders implements MiddlewareInterface
+{
+    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
+    {
+        $response = $handler->handle($request);
+
+        $path = $request->getUri()->getPath();
+        if (
+            !\in_array($request->getMethod(), ['GET', 'HEAD'], true)
+            || $response->getStatusCode() !== 200
+            || ($path !== '/_json' && !str_starts_with($path, '/_json/'))
+            || isset($request->getCookieParams()['fe_typo_user'])
+        ) {
+            return $response;
+        }
+
+        $etag = '"' . md5((string)$response->getBody()) . '"';
+
+        $ifNoneMatch = trim($request->getHeaderLine('If-None-Match'));
+        if ($ifNoneMatch !== '' && str_contains($ifNoneMatch, $etag)) {
+            return (new Response())
+                ->withStatus(304)
+                ->withHeader('ETag', $etag)
+                ->withHeader('Cache-Control', 'no-cache')
+                ->withHeader('Expires', '0');
+        }
+
+        return $response
+            ->withHeader('Cache-Control', 'no-cache')
+            ->withoutHeader('Pragma')
+            ->withHeader('Expires', '0')
+            ->withHeader('ETag', $etag);
+    }
+}
diff --git a/packages/vitec/Configuration/RequestMiddlewares.php b/packages/vitec/Configuration/RequestMiddlewares.php
index 49d6d08..1a70cbb 100755
--- a/packages/vitec/Configuration/RequestMiddlewares.php
+++ b/packages/vitec/Configuration/RequestMiddlewares.php
@@ -56,6 +56,17 @@ return [
                 'typo3/cms-core/normalized-params-attribute',
             ],
         ],
+        // Outer response filter: Cache-Control: no-cache + ETag/304 for
+        // /_json (tickets 0011-FE / 0055-BE).
+        'vitec/json-cache-headers' => [
+            'target' => \Evomedien\Vitec\Middleware\JsonCacheHeaders::class,
+            'after' => [
+                'typo3/cms-core/normalized-params-attribute',
+            ],
+            'before' => [
+                'vitec/json-prefix-rewrite',
+            ],
+        ],
     ],
     'backend' => [
         'vitec/sync-ssr-flag' => [
diff --git a/public/.htaccess b/public/.htaccess
index 20d9563..09bb851 100644
--- a/public/.htaccess
+++ b/public/.htaccess
@@ -439,9 +439,15 @@ Options -MultiViews
 	Header set X-Content-Type-Options "nosniff"
 </IfModule>
 
-# ETag removal
+# ETag removal - except for the /_json API: there TYPO3 (JsonCacheHeaders
+# middleware) sends a content ETag so browsers can revalidate with 304
+# (tickets 0011-FE / 0055-BE).
 <IfModule mod_headers.c>
-	Header unset ETag
+	SetEnvIf Request_URI "^/_json($|/)" KEEP_ETAG=1
+	# After the mod_rewrite internal redirect to index.php the variable
+	# is renamed REDIRECT_KEEP_ETAG - carry it back over:
+	SetEnvIf REDIRECT_KEEP_ETAG 1 KEEP_ETAG=1
+	Header unset ETag env=!KEEP_ETAG
 </IfModule>
 FileETag None