diff --git a/src/Controller/XmlSitemapController.php b/src/Controller/XmlSitemapController.php
index 9bf37482c2b98567fa29c61285d04ab09851051f..2df3e4dc5b8aa011440797aa4a8aeedefc61b9f7 100644
--- a/src/Controller/XmlSitemapController.php
+++ b/src/Controller/XmlSitemapController.php
@@ -2,13 +2,14 @@
 
 namespace Drupal\xmlsitemap\Controller;
 
+use Drupal\Component\Serialization\Json;
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\xmlsitemap\Entity\XmlSitemap;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\Core\State\StateInterface;
-use Drupal\Core\Template\TwigEnvironment;
+use Symfony\Component\HttpFoundation\Request;
 
 /**
  * Class for Xml Sitemap Controller.
@@ -25,24 +26,14 @@ class XmlSitemapController extends ControllerBase {
    */
   protected $state;
 
-  /**
-   * The twig loader object.
-   *
-   * @var \Drupal\Core\Template\TwigEnvironment
-   */
-  protected $twig;
-
   /**
    * Constructs a new XmlSitemapController object.
    *
    * @param \Drupal\Core\State\StateInterface $state
    *   The state service.
-   * @param Drupal\Core\Template\TwigEnvironment $twig
-   *   Twig environment for Drupal.
    */
-  public function __construct(StateInterface $state, TwigEnvironment $twig) {
+  public function __construct(StateInterface $state) {
     $this->state = $state;
-    $this->twig = $twig;
   }
 
   /**
@@ -50,43 +41,54 @@ class XmlSitemapController extends ControllerBase {
    */
   public static function create(ContainerInterface $container) {
     return new static(
-      $container->get('state'),
-      $container->get('twig')
+      $container->get('state')
     );
   }
 
   /**
    * Provides the sitemap in XML format.
    *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object.
+   *
    * @throws NotFoundHttpException
    *
    * @return \Symfony\Component\HttpFoundation\Response
    *   The sitemap in XML format or plain text if xmlsitemap_developer_mode flag
    *   is set.
    */
-  public function renderSitemapXml() {
+  public function renderSitemapXml(Request $request) {
+    $headers = [];
+
+    if ($this->state->get('xmlsitemap_developer_mode')) {
+      $headers['X-XmlSitemap-Current-Context'] = Json::encode(xmlsitemap_get_current_context());
+      $headers['X-XmlSitemap'] = 'NOT FOUND';
+    }
+
     $sitemap = XmlSitemap::loadByContext();
     if (!$sitemap) {
-      throw new NotFoundHttpException();
+      $exception = new NotFoundHttpException();
+      $exception->setHeaders($headers);
+      throw $exception;
     }
-    $chunk = xmlsitemap_get_current_chunk($sitemap);
+
+    $chunk = xmlsitemap_get_current_chunk($sitemap, $request);
     $file = xmlsitemap_sitemap_get_file($sitemap, $chunk);
 
-    // Provide debugging information if enabled.
+    // Provide debugging information via headers.
     if ($this->state->get('xmlsitemap_developer_mode')) {
-      $module_path = drupal_get_path('module', 'xmlsitemap');
-      $template = $this->twig->loadTemplate($module_path . '/templates/sitemap-developer-mode.html.twig');
-      $elements = [
-        'current_context' => print_r(xmlsitemap_get_current_context(), TRUE),
-        'sitemap' => print_r($sitemap, TRUE),
-        'chunk' => $chunk,
-        'cache_file_location' => $file,
-        'cache_file_exists' => file_exists($file) ? 'Yes' : 'No',
-      ];
-      return new Response($template->render($elements));
+      $headers['X-XmlSitemap'] = Json::encode($sitemap->toArray());
+      $headers['X-XmlSitemap-Cache-File'] = $file;
+      $headers['X-XmlSitemap-Cache-Hit'] = file_exists($file) ? 'HIT' : 'MISS';
     }
-    $response = new Response();
-    return xmlsitemap_output_file($response, $file);
+
+    if (!is_file($file) || !is_readable($file)) {
+      $exception = new NotFoundHttpException();
+      $exception->setHeaders($headers);
+      throw $exception;
+    }
+
+    return xmlsitemap_output_file(new Response(), $file, $headers);
   }
 
   /**
@@ -122,7 +124,7 @@ class XmlSitemapController extends ControllerBase {
     // Output the XSL content.
     $response = new Response($xsl_content);
     $response->headers->set('Content-type', 'application/xml; charset=utf-8');
-    $response->headers->set('X-Robots-Tag', 'noindex, follow');
+    $response->headers->set('X-Robots-Tag', 'noindex, nofollow');
     return $response;
   }
 
diff --git a/templates/sitemap-developer-mode.html.twig b/templates/sitemap-developer-mode.html.twig
deleted file mode 100644
index a263d6e1e3764d28faa7b94e4bf26c4ebea42849..0000000000000000000000000000000000000000
--- a/templates/sitemap-developer-mode.html.twig
+++ /dev/null
@@ -1,43 +0,0 @@
-{#
-/**
- * @file
- * Sitemap template output when developer_mode flag is set.
- *
- * Available variables:
- * - current_context: The current context.
- *   - language: The langcode of the context.
- * - sitemap: The sitemap object to be displayed.
- *   - uri: Sitemap uri.
- *   - id: Entity id.
- *   - label: Entity label.
- *   - chunks: Number of chunks of the sitemap.
- *   - max_filesize: Maximum filesize allowed for sitemap XML file.
- *   - context: Context of the sitemap.
- *   - updated: Last time when sitemap was updated.
- *   - originalId: The original ID of the configuration entity.
- *   - pluginConfigKey: The name of the property that is used to store plugin
- *     configuration.
- *   - status: The enabled/disabled status of the configuration entity.
- *   - isSyncing: Whether the config is being created, updated or deleted
- *     through the import process.
- *   - isUninstalling: Whether the config is being deleted by the uninstall
- *     process.
- *   - uuid: Unique identified for the sitemap entity.
- *   - langcode: The language code of the entity's default language.
- *   - entityTypeId: The entity type.
- *   - enforceIsNew: Boolean indicating whether the entity should be forced to
- *     be new.
- *   - _serviceIds: Services that are used for this sitemap entity.
- *   - dependencies: Dependencies for the sitemap.
- * - chunk: Current chunk of the sitemap.
- * - cache_file_location: Path for the sitemap cache file.
- * - cache_file_exists: Boolean indicating if the sitemap cache file exists.
- *
- * @see Drupal\xmlsitemap\Controller\XmlSitemapController::renderSitemapXml()
- */
-#}
-Current context: {{ current_context }} <br />
-Sitemap: {{ sitemap }} <br />
-Chunk: {{ chunk }} <br />
-Cache file location: {{ cache_file_location }} <br />
-Cache file exists: {{ cache_file_exists }} <br />
diff --git a/xmlsitemap.module b/xmlsitemap.module
index 7b2230e0d813acb34ae04629f934b3c8d5e3f009..d48975439a94420021ec11a85219d5e1d5448df1 100644
--- a/xmlsitemap.module
+++ b/xmlsitemap.module
@@ -28,6 +28,7 @@ use Drupal\Core\Url;
 use Drupal\xmlsitemap\Entity\XmlSitemap;
 use Drupal\xmlsitemap\XmlSitemapInterface;
 use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
 /**
@@ -2198,13 +2199,19 @@ function xmlsitemap_get_status_options($default = NULL) {
  *
  * @param \Drupal\xmlsitemap\XmlSitemapInterface $sitemap
  *   Sitemap entity.
+ * @param \Symfony\Component\HttpFoundation\Request $request
+ *   The request to use if provided, otherwise \Drupal::request() will be used.
  *
  * @return int|string
  *   Returns current chunk of the sitemap.
  */
-function xmlsitemap_get_current_chunk(XmlSitemapInterface $sitemap) {
-  // Check if we should be displaing the index.
-  $query = \Drupal::request()->query;
+function xmlsitemap_get_current_chunk(XmlSitemapInterface $sitemap, Request $request = NULL) {
+  if (!isset($request)) {
+    $request = \Drupal::request();
+  }
+
+  // Check if we should display the index.
+  $query = $request->query;
   $query_page = $query->get('page');
   if (!isset($query_page) || !is_numeric($query_page)) {
     if ($sitemap->getChunks() > 1) {
@@ -2237,8 +2244,11 @@ function xmlsitemap_get_current_chunk(XmlSitemapInterface $sitemap) {
  */
 function xmlsitemap_output_file(Response $response, $file, array $headers = []) {
   if (!file_exists($file) || !is_readable($file)) {
-    throw new NotFoundHttpException();
+    $exception = new NotFoundHttpException();
+    $exception->setHeaders($headers);
+    throw $exception;
   }
+
   $mtime = filemtime($file);
   $last_modified = gmdate(DATE_RFC1123, $mtime);
   $etag = '"' . md5($last_modified) . '"';
@@ -2248,6 +2258,7 @@ function xmlsitemap_output_file(Response $response, $file, array $headers = [])
   $if_modified_since = $request->server->has('HTTP_IF_MODIFIED_SINCE') ? stripslashes($request->server->get('HTTP_IF_MODIFIED_SINCE')) : FALSE;
   $if_none_match = $request->server->has('HTTP_IF_NONE_MATCH') ? stripslashes($request->server->get('HTTP_IF_NONE_MATCH')) : FALSE;
   if ($if_modified_since && $if_none_match && $if_none_match == $etag && $if_modified_since == $last_modified) {
+    $response->headers->add($headers);
     $response->setNotModified();
     // All 304 responses must send an etag if the 200 response for the same
     // object contained an etag.