diff --git a/app/Access/Oidc/OidcService.php b/app/Access/Oidc/OidcService.php
index a84bd3205..19120e2d3 100644
--- a/app/Access/Oidc/OidcService.php
+++ b/app/Access/Oidc/OidcService.php
@@ -80,6 +80,7 @@ class OidcService
         $provider->setPkceCode($pkceCode);
 
         // Try to exchange authorization code for access token
+        /** @var OidcAccessToken $accessToken */
         $accessToken = $provider->getAccessToken('authorization_code', [
             'code' => $authorizationCode,
         ]);
diff --git a/app/Activity/ActivityQueries.php b/app/Activity/ActivityQueries.php
index d5b047937..a3383e809 100644
--- a/app/Activity/ActivityQueries.php
+++ b/app/Activity/ActivityQueries.php
@@ -11,6 +11,7 @@ use BookStack\Entities\Tools\MixedEntityListLoader;
 use BookStack\Permissions\PermissionApplicator;
 use BookStack\Users\Models\User;
 use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Collection;
 use Illuminate\Database\Eloquent\Relations\MorphTo;
 use Illuminate\Database\Eloquent\Relations\Relation;
 
@@ -27,6 +28,7 @@ class ActivityQueries
      */
     public function latest(int $count = 20, int $page = 0): array
     {
+        /** @var Collection<int, Activity> $activityList */
         $activityList = $this->permissions
             ->restrictEntityRelationQuery(Activity::query(), 'activities', 'loggable_id', 'loggable_type')
             ->orderBy('created_at', 'desc')
@@ -83,6 +85,7 @@ class ActivityQueries
      */
     public function userActivity(User $user, int $count = 20, int $page = 0): array
     {
+        /** @var Collection<int, Activity> $activityList */
         $activityList = $this->permissions
             ->restrictEntityRelationQuery(Activity::query(), 'activities', 'loggable_id', 'loggable_type')
             ->orderBy('created_at', 'desc')
diff --git a/app/Activity/Tools/WebhookFormatter.php b/app/Activity/Tools/WebhookFormatter.php
index cb4e9cb0a..111efd5d4 100644
--- a/app/Activity/Tools/WebhookFormatter.php
+++ b/app/Activity/Tools/WebhookFormatter.php
@@ -73,13 +73,17 @@ class WebhookFormatter
         // Load entity owner, creator, updater details
         $this->addModelFormatter(
             fn ($event, $model) => ($model instanceof Entity),
-            fn ($model) => $model->load(['ownedBy', 'createdBy', 'updatedBy'])
+            function ($model) {
+                $model->load(['ownedBy', 'createdBy', 'updatedBy']);
+            }
         );
 
         // Load revision detail for page update and create events
         $this->addModelFormatter(
             fn ($event, $model) => ($model instanceof Page && ($event === ActivityType::PAGE_CREATE || $event === ActivityType::PAGE_UPDATE)),
-            fn ($model) => $model->load('currentRevision')
+            function ($model) {
+                $model->load('currentRevision');
+            }
         );
     }
 
diff --git a/app/Entities/Controllers/PageApiController.php b/app/Entities/Controllers/PageApiController.php
index 38042e670..ca8989f07 100644
--- a/app/Entities/Controllers/PageApiController.php
+++ b/app/Entities/Controllers/PageApiController.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace BookStack\Entities\Controllers;
 
 use BookStack\Activity\Tools\CommentTree;
@@ -10,7 +12,9 @@ use BookStack\Exceptions\PermissionsException;
 use BookStack\Http\ApiController;
 use BookStack\Permissions\Permission;
 use Exception;
+use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
+use Illuminate\Http\Response;
 
 class PageApiController extends ApiController
 {
@@ -45,7 +49,7 @@ class PageApiController extends ApiController
     /**
      * Get a listing of pages visible to the user.
      */
-    public function list()
+    public function list(): JsonResponse
     {
         $pages = $this->queries->visibleForList()
             ->addSelect(['created_by', 'updated_by', 'revision_count', 'editor']);
@@ -69,7 +73,7 @@ class PageApiController extends ApiController
      * Any images included via base64 data URIs will be extracted and saved as gallery
      * images against the page during upload.
      */
-    public function create(Request $request)
+    public function create(Request $request): JsonResponse
     {
         $this->validate($request, $this->rules['create']);
 
@@ -102,9 +106,9 @@ class PageApiController extends ApiController
      * Comments for the page are provided in a tree-structure representing the hierarchy of top-level
      * comments and replies, for both archived and active comments.
      */
-    public function read(string $id)
+    public function read(string $id): JsonResponse
     {
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
 
         $page = $page->forJsonDisplay();
         $commentTree = (new CommentTree($page));
@@ -124,11 +128,11 @@ class PageApiController extends ApiController
      * Providing a 'book_id' or 'chapter_id' property will essentially move
      * the page into that parent element if you have permissions to do so.
      */
-    public function update(Request $request, string $id)
+    public function update(Request $request, string $id): JsonResponse
     {
         $requestData = $this->validate($request, $this->rules['update']);
 
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
         $this->checkOwnablePermission(Permission::PageUpdate, $page);
 
         $parent = null;
@@ -161,9 +165,9 @@ class PageApiController extends ApiController
      * Delete a page.
      * This will typically send the page to the recycle bin.
      */
-    public function delete(string $id)
+    public function delete(string $id): Response
     {
-        $page = $this->queries->findVisibleByIdOrFail($id);
+        $page = $this->queries->findVisibleByIdOrFail(intval($id));
         $this->checkOwnablePermission(Permission::PageDelete, $page);
 
         $this->pageRepo->destroy($page);
diff --git a/app/Entities/Controllers/PageController.php b/app/Entities/Controllers/PageController.php
index 82edfbc27..dd655e7ab 100644
--- a/app/Entities/Controllers/PageController.php
+++ b/app/Entities/Controllers/PageController.php
@@ -25,6 +25,7 @@ use BookStack\Util\HtmlContentFilter;
 use BookStack\Util\HtmlContentFilterConfig;
 use Exception;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
+use Illuminate\Database\Eloquent\Relations\Relation;
 use Illuminate\Http\Request;
 use Illuminate\Validation\ValidationException;
 use Throwable;
@@ -358,8 +359,8 @@ class PageController extends Controller
      */
     public function showRecentlyUpdated()
     {
-        $visibleBelongsScope = function (BelongsTo $query) {
-            $query->scopes('visible');
+        $visibleBelongsScope = function (Relation $relation): void {
+            $relation->scopes('visible');
         };
 
         $pages = $this->queries->visibleForList()
diff --git a/app/Entities/Controllers/PageRevisionController.php b/app/Entities/Controllers/PageRevisionController.php
index cc6b79bfe..801aeed3e 100644
--- a/app/Entities/Controllers/PageRevisionController.php
+++ b/app/Entities/Controllers/PageRevisionController.php
@@ -177,7 +177,7 @@ class PageRevisionController extends Controller
      */
     public function destroyUserDraft(string $pageId)
     {
-        $page = $this->pageQueries->findVisibleByIdOrFail($pageId);
+        $page = $this->pageQueries->findVisibleByIdOrFail(intval($pageId));
         $this->revisionRepo->deleteDraftsForCurrentUser($page);
 
         return response('', 200);
diff --git a/app/Entities/Tools/Markdown/CustomListItemRenderer.php b/app/Entities/Tools/Markdown/CustomListItemRenderer.php
index 0c506d7f9..14cdaa2ea 100644
--- a/app/Entities/Tools/Markdown/CustomListItemRenderer.php
+++ b/app/Entities/Tools/Markdown/CustomListItemRenderer.php
@@ -25,9 +25,13 @@ class CustomListItemRenderer implements NodeRendererInterface
      */
     public function render(Node $node, ChildNodeRendererInterface $childRenderer)
     {
+        if (!($node instanceof ListItem)) {
+            return null;
+        }
+
         $listItem = $this->baseRenderer->render($node, $childRenderer);
 
-        if ($node instanceof ListItem && $this->startsTaskListItem($node) && $listItem instanceof HtmlElement) {
+        if ($this->startsTaskListItem($node) && $listItem instanceof HtmlElement) {
             $listItem->setAttribute('class', 'task-list-item');
         }
 
diff --git a/app/Entities/Tools/PageContent.php b/app/Entities/Tools/PageContent.php
index 9fb4596f5..c66dcbe41 100644
--- a/app/Entities/Tools/PageContent.php
+++ b/app/Entities/Tools/PageContent.php
@@ -421,28 +421,41 @@ class PageContent
      */
     protected function headerNodesToLevelList(DOMNodeList $nodeList): array
     {
-        $tree = collect($nodeList)->map(function (DOMElement $header) {
+        $minLevel = 6;
+
+        $headerDetails = array_map(function (DOMNode $header) use (&$minLevel) {
+            if (!$header instanceof DOMElement) {
+                return null;
+            }
+
             $text = trim(str_replace("\xc2\xa0", ' ', $header->nodeValue));
             $text = mb_substr($text, 0, 100);
 
+            if (empty($text)) {
+                return null;
+            }
+
+            $level = intval(str_replace('h', '', $header->nodeName));
+            if ($level < $minLevel) {
+                $minLevel = $level;
+            }
+
             return [
                 'nodeName' => strtolower($header->nodeName),
-                'level'    => intval(str_replace('h', '', $header->nodeName)),
+                'level'    => $level,
                 'link'     => '#' . $header->getAttribute('id'),
                 'text'     => $text,
             ];
-        })->filter(function ($header) {
-            return mb_strlen($header['text']) > 0;
-        });
+        }, [...$nodeList]);
+
+        $filtered = array_values(array_filter($headerDetails));
 
         // Shift headers if only smaller headers have been used
-        $levelChange = ($tree->pluck('level')->min() - 1);
-        $tree = $tree->map(function ($header) use ($levelChange) {
-            $header['level'] -= ($levelChange);
+        $levelChange = ($minLevel - 1);
+        foreach ($filtered as $index => $header) {
+            $filtered[$index]['level'] -= $levelChange;
+        }
 
-            return $header;
-        });
-
-        return $tree->toArray();
+        return $filtered;
     }
 }
diff --git a/app/Entities/Tools/PageIncludeParser.php b/app/Entities/Tools/PageIncludeParser.php
index af7ed4fc6..16917f41c 100644
--- a/app/Entities/Tools/PageIncludeParser.php
+++ b/app/Entities/Tools/PageIncludeParser.php
@@ -192,10 +192,10 @@ class PageIncludeParser
     /**
      * Get the parent paragraph of the given node, if existing.
      */
-    protected function getParentParagraph(DOMNode $parent): ?DOMNode
+    protected function getParentParagraph(DOMNode $parent): ?DOMElement
     {
         do {
-            if (strtolower($parent->nodeName) === 'p') {
+            if (strtolower($parent->nodeName) === 'p' && $parent instanceof DOMElement) {
                 return $parent;
             }
 
diff --git a/app/Entities/Tools/SlugGenerator.php b/app/Entities/Tools/SlugGenerator.php
index 6eec84a91..ac003b97a 100644
--- a/app/Entities/Tools/SlugGenerator.php
+++ b/app/Entities/Tools/SlugGenerator.php
@@ -52,7 +52,7 @@ class SlugGenerator
     {
         $slug = Str::slug($name);
         if ($slug === '') {
-            $slug = substr(md5(rand(1, 500)), 0, 5);
+            $slug = substr(md5(strval(rand(1, 500))), 0, 5);
         }
 
         return $slug;