diff --git a/core/basethemelet.php b/core/basethemelet.php
index 010b2e1b..b1ded94f 100644
--- a/core/basethemelet.php
+++ b/core/basethemelet.php
@@ -107,7 +107,7 @@ class BaseThemelet
         );
     }
 
-    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false)
+    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false): void
     {
         if ($total_pages == 0) {
             $total_pages = 1;
diff --git a/ext/admin/theme.php b/ext/admin/theme.php
index 27bacdfa..521e0104 100644
--- a/ext/admin/theme.php
+++ b/ext/admin/theme.php
@@ -9,7 +9,7 @@ class AdminPageTheme extends Themelet
     /*
      * Show the basics of a page, for other extensions to add to
      */
-    public function display_page()
+    public function display_page(): void
     {
         global $page;
 
diff --git a/ext/approval/theme.php b/ext/approval/theme.php
index 6701e41b..61488868 100644
--- a/ext/approval/theme.php
+++ b/ext/approval/theme.php
@@ -40,13 +40,13 @@ class ApprovalTheme extends Themelet
         );
     }
 
-    public function display_admin_block(SetupBuildingEvent $event)
+    public function display_admin_block(SetupBuildingEvent $event): void
     {
         $sb = $event->panel->create_new_block("Approval");
         $sb->add_bool_option(ApprovalConfig::IMAGES, "Posts: ");
     }
 
-    public function display_admin_form()
+    public function display_admin_form(): void
     {
         global $page;
 
diff --git a/ext/biography/theme.php b/ext/biography/theme.php
index 83857d13..37e91e86 100644
--- a/ext/biography/theme.php
+++ b/ext/biography/theme.php
@@ -8,12 +8,12 @@ use function MicroHTML\TEXTAREA;
 
 class BiographyTheme extends Themelet
 {
-    public function display_biography(Page $page, string $bio)
+    public function display_biography(Page $page, string $bio): void
     {
         $page->add_block(new Block("About Me", format_text($bio), "main", 30, "about-me"));
     }
 
-    public function display_composer(Page $page, string $bio)
+    public function display_composer(Page $page, string $bio): void
     {
         $html = SHM_SIMPLE_FORM(
             make_link("biography"),
diff --git a/ext/blocks/theme.php b/ext/blocks/theme.php
index 1757cb81..7dc73c46 100644
--- a/ext/blocks/theme.php
+++ b/ext/blocks/theme.php
@@ -16,7 +16,7 @@ use function MicroHTML\OPTION;
 
 class BlocksTheme extends Themelet
 {
-    public function display_blocks($blocks)
+    public function display_blocks($blocks): void
     {
         global $page;
 
diff --git a/ext/blotter/theme.php b/ext/blotter/theme.php
index e01098ee..7944d895 100644
--- a/ext/blotter/theme.php
+++ b/ext/blotter/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class BlotterTheme extends Themelet
 {
-    public function display_editor($entries)
+    public function display_editor($entries): void
     {
         global $page;
         $html = $this->get_html_for_blotter_editor($entries);
@@ -16,7 +16,7 @@ class BlotterTheme extends Themelet
         $page->add_block(new Block("Navigation", "<a href='".make_link()."'>Index</a>", "left", 0));
     }
 
-    public function display_blotter_page($entries)
+    public function display_blotter_page($entries): void
     {
         global $page;
         $html = $this->get_html_for_blotter_page($entries);
diff --git a/ext/bulk_actions/theme.php b/ext/bulk_actions/theme.php
index 608b7778..e9af61fa 100644
--- a/ext/bulk_actions/theme.php
+++ b/ext/bulk_actions/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class BulkActionsTheme extends Themelet
 {
-    public function display_selector(Page $page, array $actions, string $query)
+    public function display_selector(Page $page, array $actions, string $query): void
     {
         $body = "<input type='hidden' name='bulk_selected_ids' id='bulk_selected_ids' />
 				<input id='bulk_selector_activate' type='button' onclick='activate_bulk_selector();' value='Activate (M)anual Select' accesskey='m'/>
diff --git a/ext/bulk_add/theme.php b/ext/bulk_add/theme.php
index 63b30410..339bfd5b 100644
--- a/ext/bulk_add/theme.php
+++ b/ext/bulk_add/theme.php
@@ -13,7 +13,7 @@ class BulkAddTheme extends Themelet
      *
      * @param UploadResult[] $results
      */
-    public function display_upload_results(Page $page, array $results)
+    public function display_upload_results(Page $page, array $results): void
     {
         $page->set_title("Adding folder");
         $page->set_heading("Adding folder");
@@ -34,7 +34,7 @@ class BulkAddTheme extends Themelet
      * links to bulk_add with POST[dir] set to the name of a server-side
      * directory full of images
      */
-    public function display_admin_block()
+    public function display_admin_block(): void
     {
         global $page;
         $html = "
diff --git a/ext/bulk_add_csv/theme.php b/ext/bulk_add_csv/theme.php
index 2128e5ae..26b1b50d 100644
--- a/ext/bulk_add_csv/theme.php
+++ b/ext/bulk_add_csv/theme.php
@@ -11,7 +11,7 @@ class BulkAddCSVTheme extends Themelet
     /*
      * Show a standard page for results to be put into
      */
-    public function display_upload_results(Page $page)
+    public function display_upload_results(Page $page): void
     {
         $page->set_title("Adding posts from csv");
         $page->set_heading("Adding posts from csv");
@@ -26,7 +26,7 @@ class BulkAddCSVTheme extends Themelet
      * links to bulk_add_csv with POST[csv] set to the name of a server-side
      * csv file
      */
-    public function display_admin_block()
+    public function display_admin_block(): void
     {
         global $page;
         $html = "
diff --git a/ext/comment/theme.php b/ext/comment/theme.php
index 911b4eb0..ee628315 100644
--- a/ext/comment/theme.php
+++ b/ext/comment/theme.php
@@ -13,7 +13,7 @@ class CommentListTheme extends Themelet
     /**
      * Display a page with a list of images, and for each image, the image's comments.
      */
-    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post)
+    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post): void
     {
         global $config, $page, $user;
 
@@ -91,7 +91,7 @@ class CommentListTheme extends Themelet
         }
     }
 
-    public function display_admin_block()
+    public function display_admin_block(): void
     {
         global $page;
 
@@ -113,7 +113,7 @@ class CommentListTheme extends Themelet
      *
      * @param Comment[] $comments An array of Comment objects to be shown
      */
-    public function display_recent_comments(array $comments)
+    public function display_recent_comments(array $comments): void
     {
         global $page;
         $this->show_anon_id = false;
@@ -130,7 +130,7 @@ class CommentListTheme extends Themelet
      *
      * @param Comment[] $comments
      */
-    public function display_image_comments(Image $image, array $comments, bool $postbox)
+    public function display_image_comments(Image $image, array $comments, bool $postbox): void
     {
         global $page;
         $this->show_anon_id = true;
@@ -149,7 +149,7 @@ class CommentListTheme extends Themelet
      *
      * @param Comment[] $comments
      */
-    public function display_recent_user_comments(array $comments, User $user)
+    public function display_recent_user_comments(array $comments, User $user): void
     {
         global $page;
         $html = "";
@@ -164,7 +164,7 @@ class CommentListTheme extends Themelet
         $page->add_block(new Block("Comments", $html, "left", 70, "comment-list-user"));
     }
 
-    public function display_all_user_comments(array $comments, int $page_number, int $total_pages, User $user)
+    public function display_all_user_comments(array $comments, int $page_number, int $total_pages, User $user): void
     {
         global $page;
 
diff --git a/ext/cron_uploader/theme.php b/ext/cron_uploader/theme.php
index 6d89890c..6fe7e5d4 100644
--- a/ext/cron_uploader/theme.php
+++ b/ext/cron_uploader/theme.php
@@ -159,7 +159,7 @@ class CronUploaderTheme extends Themelet
         return (string)$html;
     }
 
-    public function display_form(array $failed_dirs)
+    public function display_form(array $failed_dirs): void
     {
         global $page;
 
diff --git a/ext/downtime/theme.php b/ext/downtime/theme.php
index 1a21d9ae..495c7cd6 100644
--- a/ext/downtime/theme.php
+++ b/ext/downtime/theme.php
@@ -9,7 +9,7 @@ class DowntimeTheme extends Themelet
     /**
      * Show the admin that downtime mode is enabled
      */
-    public function display_notification(Page $page)
+    public function display_notification(Page $page): void
     {
         $page->add_block(new Block(
             "Downtime",
@@ -22,7 +22,7 @@ class DowntimeTheme extends Themelet
     /**
      * Display $message and exit
      */
-    public function display_message(string $message)
+    public function display_message(string $message): void
     {
         global $config, $user, $page;
         $theme_name = $config->get_string(SetupConfig::THEME);
diff --git a/ext/emoticons_list/theme.php b/ext/emoticons_list/theme.php
index 1f01a34b..d53d637f 100644
--- a/ext/emoticons_list/theme.php
+++ b/ext/emoticons_list/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class EmoticonListTheme extends Themelet
 {
-    public function display_emotes(array $list)
+    public function display_emotes(array $list): void
     {
         global $page;
         $data_href = get_base_href();
diff --git a/ext/et/theme.php b/ext/et/theme.php
index 958075a1..9d908ac6 100644
--- a/ext/et/theme.php
+++ b/ext/et/theme.php
@@ -16,7 +16,7 @@ class ETTheme extends Themelet
      *
      * $info = an array of ($name => $value)
      */
-    public function display_info_page($yaml)
+    public function display_info_page($yaml): void
     {
         global $page;
 
diff --git a/ext/ext_manager/theme.php b/ext/ext_manager/theme.php
index 3631f7bb..8d368390 100644
--- a/ext/ext_manager/theme.php
+++ b/ext/ext_manager/theme.php
@@ -27,7 +27,7 @@ class ExtManagerTheme extends Themelet
     /**
      * @param ExtensionInfo[] $extensions
      */
-    public function display_table(Page $page, array $extensions, bool $editable)
+    public function display_table(Page $page, array $extensions, bool $editable): void
     {
         $tbody = TBODY();
 
@@ -104,7 +104,7 @@ class ExtManagerTheme extends Themelet
         $page->add_block(new Block("Extension Manager", $form));
     }
 
-    public function display_doc(Page $page, ExtensionInfo $info)
+    public function display_doc(Page $page, ExtensionInfo $info): void
     {
         $author = emptyHTML();
         if (count($info->authors) > 0) {
diff --git a/ext/forum/theme.php b/ext/forum/theme.php
index 2d49021d..a37e3719 100644
--- a/ext/forum/theme.php
+++ b/ext/forum/theme.php
@@ -10,7 +10,7 @@ use function MicroHTML\{INPUT, LABEL, SMALL, TEXTAREA, TR, TD, TABLE, TH, TBODY,
 
 class ForumTheme extends Themelet
 {
-    public function display_thread_list(Page $page, $threads, $showAdminOptions, $pageNumber, $totalPages)
+    public function display_thread_list(Page $page, $threads, $showAdminOptions, $pageNumber, $totalPages): void
     {
         if (count($threads) == 0) {
             $html = "There are no threads to show.";
@@ -27,7 +27,7 @@ class ForumTheme extends Themelet
 
 
 
-    public function display_new_thread_composer(Page $page, $threadText = null, $threadTitle = null)
+    public function display_new_thread_composer(Page $page, $threadText = null, $threadTitle = null): void
     {
         global $config, $user;
         $max_characters = $config->get_int('forumMaxCharsPerPost');
@@ -75,7 +75,7 @@ class ForumTheme extends Themelet
 
 
 
-    public function display_new_post_composer(Page $page, $threadID)
+    public function display_new_post_composer(Page $page, $threadID): void
     {
         global $config;
 
@@ -109,7 +109,7 @@ class ForumTheme extends Themelet
 
 
 
-    public function display_thread($posts, $showAdminOptions, $threadTitle, $threadID, $pageNumber, $totalPages)
+    public function display_thread($posts, $showAdminOptions, $threadTitle, $threadID, $pageNumber, $totalPages): void
     {
         global $config, $page/*, $user*/;
 
diff --git a/ext/handle_cbz/theme.php b/ext/handle_cbz/theme.php
index 5d6dff37..5ff89f3b 100644
--- a/ext/handle_cbz/theme.php
+++ b/ext/handle_cbz/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CBZFileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $page;
         $data_href = get_base_href();
diff --git a/ext/handle_ico/theme.php b/ext/handle_ico/theme.php
index 2f2587c0..39405e2c 100644
--- a/ext/handle_ico/theme.php
+++ b/ext/handle_ico/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class IcoFileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $page;
         $ilink = $image->get_image_link();
diff --git a/ext/handle_mp3/theme.php b/ext/handle_mp3/theme.php
index a42a3a16..b7702919 100644
--- a/ext/handle_mp3/theme.php
+++ b/ext/handle_mp3/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class MP3FileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $page;
         $data_href = get_base_href();
diff --git a/ext/handle_pixel/theme.php b/ext/handle_pixel/theme.php
index 0ffebd77..da3e7f4b 100644
--- a/ext/handle_pixel/theme.php
+++ b/ext/handle_pixel/theme.php
@@ -8,7 +8,7 @@ use function MicroHTML\IMG;
 
 class PixelFileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $config, $page;
 
@@ -25,7 +25,7 @@ class PixelFileHandlerTheme extends Themelet
         $page->add_block(new Block("Image", $html, "main", 10));
     }
 
-    public function display_metadata(Image $image)
+    public function display_metadata(Image $image): void
     {
         global $page;
 
diff --git a/ext/handle_svg/theme.php b/ext/handle_svg/theme.php
index a9fd63df..a37d0051 100644
--- a/ext/handle_svg/theme.php
+++ b/ext/handle_svg/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class SVGFileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $page;
         $ilink = make_link("get_svg/{$image->id}/{$image->id}.svg");
diff --git a/ext/handle_video/theme.php b/ext/handle_video/theme.php
index dcb70208..24664cc0 100644
--- a/ext/handle_video/theme.php
+++ b/ext/handle_video/theme.php
@@ -8,7 +8,7 @@ use function MicroHTML\{A, BR, VIDEO, SOURCE, emptyHTML};
 
 class VideoFileHandlerTheme extends Themelet
 {
-    public function display_image(Image $image)
+    public function display_image(Image $image): void
     {
         global $config, $page;
 
diff --git a/ext/help_pages/theme.php b/ext/help_pages/theme.php
index a3987c42..60c6a426 100644
--- a/ext/help_pages/theme.php
+++ b/ext/help_pages/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class HelpPagesTheme extends Themelet
 {
-    public function display_list_page(array $pages)
+    public function display_list_page(array $pages): void
     {
         global $page;
 
@@ -23,7 +23,7 @@ class HelpPagesTheme extends Themelet
         $page->add_block(new Block("Help Pages", "See list of pages to left"));
     }
 
-    public function display_help_page(string $title)
+    public function display_help_page(string $title): void
     {
         global $page;
 
diff --git a/ext/holiday/theme.php b/ext/holiday/theme.php
index 762e0b99..b1504ccc 100644
--- a/ext/holiday/theme.php
+++ b/ext/holiday/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class HolidayTheme extends Themelet
 {
-    public function display_holiday(?string $holiday)
+    public function display_holiday(?string $holiday): void
     {
         global $page;
         if ($holiday) {
diff --git a/ext/index/theme.php b/ext/index/theme.php
index 9932eb1f..6b7eac27 100644
--- a/ext/index/theme.php
+++ b/ext/index/theme.php
@@ -22,7 +22,7 @@ class IndexTheme extends Themelet
         $this->search_terms = $search_terms;
     }
 
-    public function display_intro(Page $page)
+    public function display_intro(Page $page): void
     {
         $text = "
 <div style='text-align: left;'>
@@ -44,7 +44,7 @@ and of course start organising your images :-)
     /**
      * @param Image[] $images
      */
-    public function display_page(Page $page, array $images)
+    public function display_page(Page $page, array $images): void
     {
         $this->display_shortwiki($page);
 
@@ -63,7 +63,7 @@ and of course start organising your images :-)
     /**
      * @param string[] $parts
      */
-    public function display_admin_block(array $parts)
+    public function display_admin_block(array $parts): void
     {
         global $page;
         $page->add_block(new Block("List Controls", join("<br>", $parts), "left", 50));
diff --git a/ext/ipban/theme.php b/ext/ipban/theme.php
index 996b40a7..6697a065 100644
--- a/ext/ipban/theme.php
+++ b/ext/ipban/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class IPBanTheme extends Themelet
 {
-    public function display_bans(Page $page, $table, $paginator)
+    public function display_bans(Page $page, $table, $paginator): void
     {
         $html = "
 			<a href='".make_link("ip_ban/list", "r__size=1000000")."'>Show All Active</a> /
diff --git a/ext/log_db/theme.php b/ext/log_db/theme.php
index fa12da1b..a44c0ed9 100644
--- a/ext/log_db/theme.php
+++ b/ext/log_db/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class LogDatabaseTheme extends Themelet
 {
-    public function display_events($table, $paginator)
+    public function display_events($table, $paginator): void
     {
         global $page;
         $page->set_title("Event Log");
diff --git a/ext/not_a_tag/theme.php b/ext/not_a_tag/theme.php
index 7c23a7a3..1d2a1390 100644
--- a/ext/not_a_tag/theme.php
+++ b/ext/not_a_tag/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class NotATagTheme extends Themelet
 {
-    public function display_untags(Page $page, $table, $paginator)
+    public function display_untags(Page $page, $table, $paginator): void
     {
         $page->set_title("UnTags");
         $page->set_heading("UnTags");
diff --git a/ext/notes/theme.php b/ext/notes/theme.php
index 0755eba6..a619ad00 100644
--- a/ext/notes/theme.php
+++ b/ext/notes/theme.php
@@ -74,7 +74,7 @@ class NotesTheme extends Themelet
     }
 
 
-    public function display_note_list($images, $pageNumber, $totalPages)
+    public function display_note_list($images, $pageNumber, $totalPages): void
     {
         global $page;
         $pool_images = '';
@@ -94,7 +94,7 @@ class NotesTheme extends Themelet
         $page->add_block(new Block("Notes", $pool_images, "main", 20));
     }
 
-    public function display_note_requests($images, $pageNumber, $totalPages)
+    public function display_note_requests($images, $pageNumber, $totalPages): void
     {
         global $page;
 
@@ -157,7 +157,7 @@ class NotesTheme extends Themelet
         return $html;
     }
 
-    public function display_histories($histories, $pageNumber, $totalPages)
+    public function display_histories($histories, $pageNumber, $totalPages): void
     {
         global $page;
 
@@ -170,7 +170,7 @@ class NotesTheme extends Themelet
         $this->display_paginator($page, "note/updated", null, $pageNumber, $totalPages);
     }
 
-    public function display_history($histories, $pageNumber, $totalPages)
+    public function display_history($histories, $pageNumber, $totalPages): void
     {
         global $page;
 
diff --git a/ext/pm/theme.php b/ext/pm/theme.php
index c80e7f50..26817382 100644
--- a/ext/pm/theme.php
+++ b/ext/pm/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class PrivMsgTheme extends Themelet
 {
-    public function display_pms(Page $page, $pms)
+    public function display_pms(Page $page, $pms): void
     {
         global $user;
 
@@ -58,7 +58,7 @@ class PrivMsgTheme extends Themelet
         $page->add_block(new Block("Private Messages", $html, "main", 40, "private-messages"));
     }
 
-    public function display_composer(Page $page, User $from, User $to, $subject = "")
+    public function display_composer(Page $page, User $from, User $to, $subject = ""): void
     {
         global $user;
         $post_url = make_link("pm/send");
@@ -79,7 +79,7 @@ EOD;
         $page->add_block(new Block("Write a PM", $html, "main", 50));
     }
 
-    public function display_message(Page $page, User $from, User $to, PM $pm)
+    public function display_message(Page $page, User $from, User $to, PM $pm): void
     {
         $page->set_title("Private Message");
         $page->set_heading(html_escape($pm->subject));
diff --git a/ext/random_image/theme.php b/ext/random_image/theme.php
index 6150609b..198598da 100644
--- a/ext/random_image/theme.php
+++ b/ext/random_image/theme.php
@@ -10,7 +10,7 @@ use function MicroHTML\IMG;
 
 class RandomImageTheme extends Themelet
 {
-    public function display_random(Page $page, Image $image)
+    public function display_random(Page $page, Image $image): void
     {
         $page->add_block(new Block("Random Post", $this->build_random_html($image), "left", 8));
     }
diff --git a/ext/random_list/theme.php b/ext/random_list/theme.php
index 8ccd5134..be0aef7c 100644
--- a/ext/random_list/theme.php
+++ b/ext/random_list/theme.php
@@ -19,7 +19,7 @@ class RandomListTheme extends Themelet
     /**
      * @param Image[] $images
      */
-    public function display_page(Page $page, array $images)
+    public function display_page(Page $page, array $images): void
     {
         $page->title = "Random Posts";
 
diff --git a/ext/rating/theme.php b/ext/rating/theme.php
index a3bb0cd0..51c3c466 100644
--- a/ext/rating/theme.php
+++ b/ext/rating/theme.php
@@ -25,7 +25,7 @@ class RatingsTheme extends Themelet
         );
     }
 
-    public function display_form(array $current_ratings)
+    public function display_form(array $current_ratings): void
     {
         global $page;
 
diff --git a/ext/regen_thumb/theme.php b/ext/regen_thumb/theme.php
index 3b720562..9a0d2ab1 100644
--- a/ext/regen_thumb/theme.php
+++ b/ext/regen_thumb/theme.php
@@ -23,7 +23,7 @@ class RegenThumbTheme extends Themelet
     /**
      * Show a link to the new thumbnail.
      */
-    public function display_results(Page $page, Image $image)
+    public function display_results(Page $page, Image $image): void
     {
         $page->set_title("Thumbnail Regenerated");
         $page->set_heading("Thumbnail Regenerated");
diff --git a/ext/replace_file/theme.php b/ext/replace_file/theme.php
index 133145dd..1eca111c 100644
--- a/ext/replace_file/theme.php
+++ b/ext/replace_file/theme.php
@@ -16,7 +16,7 @@ class ReplaceFileTheme extends Themelet
     /**
      * Only allows 1 file to be uploaded - for replacing another image file.
      */
-    public function display_replace_page(Page $page, int $image_id)
+    public function display_replace_page(Page $page, int $image_id): void
     {
         global $config, $page;
         $tl_enabled = ($config->get_string(UploadConfig::TRANSLOAD_ENGINE, "none") != "none");
diff --git a/ext/report_image/theme.php b/ext/report_image/theme.php
index 91af0b05..dfd07fbd 100644
--- a/ext/report_image/theme.php
+++ b/ext/report_image/theme.php
@@ -8,7 +8,7 @@ use function MicroHTML\INPUT;
 
 class ReportImageTheme extends Themelet
 {
-    public function display_reported_images(Page $page, array $reports)
+    public function display_reported_images(Page $page, array $reports): void
     {
         global $config, $user;
 
@@ -58,7 +58,7 @@ class ReportImageTheme extends Themelet
     /**
      * @param ImageReport[] $reports
      */
-    public function display_image_banner(Image $image, array $reports)
+    public function display_image_banner(Image $image, array $reports): void
     {
         global $config, $page;
 
diff --git a/ext/resize/theme.php b/ext/resize/theme.php
index 44937b1f..384a27c0 100644
--- a/ext/resize/theme.php
+++ b/ext/resize/theme.php
@@ -38,7 +38,7 @@ class ResizeImageTheme extends Themelet
         return $html;
     }
 
-    public function display_resize_error(Page $page, string $title, string $message)
+    public function display_resize_error(Page $page, string $title, string $message): void
     {
         $page->set_title("Resize Image");
         $page->set_heading("Resize Image");
diff --git a/ext/rotate/theme.php b/ext/rotate/theme.php
index a0d6f7e9..b5e0ba79 100644
--- a/ext/rotate/theme.php
+++ b/ext/rotate/theme.php
@@ -24,7 +24,7 @@ class RotateImageTheme extends Themelet
     /**
      * Display the error.
      */
-    public function display_rotate_error(Page $page, string $title, string $message)
+    public function display_rotate_error(Page $page, string $title, string $message): void
     {
         $page->set_title("Rotate Image");
         $page->set_heading("Rotate Image");
diff --git a/ext/setup/theme.php b/ext/setup/theme.php
index 0baa14ca..feee9949 100644
--- a/ext/setup/theme.php
+++ b/ext/setup/theme.php
@@ -17,7 +17,7 @@ class SetupTheme extends Themelet
      *
      * The page should wrap all the options in a form which links to setup_save
      */
-    public function display_page(Page $page, SetupPanel $panel)
+    public function display_page(Page $page, SetupPanel $panel): void
     {
         usort($panel->blocks, "Shimmie2\blockcmp");
 
@@ -43,7 +43,7 @@ class SetupTheme extends Themelet
         $page->add_block(new Block("Setup", $table));
     }
 
-    public function display_advanced(Page $page, $options)
+    public function display_advanced(Page $page, $options): void
     {
         $h_rows = "";
         ksort($options);
diff --git a/ext/source_history/theme.php b/ext/source_history/theme.php
index 7c6a106b..d7558d60 100644
--- a/ext/source_history/theme.php
+++ b/ext/source_history/theme.php
@@ -14,7 +14,7 @@ class SourceHistoryTheme extends Themelet
 {
     private array $messages = [];
 
-    public function display_history_page(Page $page, int $image_id, array $history)
+    public function display_history_page(Page $page, int $image_id, array $history): void
     {
         $history_html = $this->history_list($history, true);
 
@@ -24,7 +24,7 @@ class SourceHistoryTheme extends Themelet
         $page->add_block(new Block("Source History", $history_html, "main", 10));
     }
 
-    public function display_global_page(Page $page, array $history, int $page_number)
+    public function display_global_page(Page $page, array $history, int $page_number): void
     {
         $history_html = $this->history_list($history, false);
 
@@ -44,7 +44,7 @@ class SourceHistoryTheme extends Themelet
     /**
      * Add a section to the admin page.
      */
-    public function display_admin_block(string $validation_msg = '')
+    public function display_admin_block(string $validation_msg = ''): void
     {
         global $page;
 
@@ -71,7 +71,7 @@ class SourceHistoryTheme extends Themelet
     /*
      * Show a standard page for results to be put into
      */
-    public function display_revert_ip_results()
+    public function display_revert_ip_results(): void
     {
         global $page;
         $html = implode("\n", $this->messages);
diff --git a/ext/tag_edit/theme.php b/ext/tag_edit/theme.php
index 325a390b..08e7997c 100644
--- a/ext/tag_edit/theme.php
+++ b/ext/tag_edit/theme.php
@@ -14,7 +14,7 @@ class TagEditTheme extends Themelet
      * Display a form which links to tag_edit/replace with POST[search]
      * and POST[replace] set appropriately
      */
-    public function display_mass_editor()
+    public function display_mass_editor(): void
     {
         global $page;
         $html = "
diff --git a/ext/tag_history/theme.php b/ext/tag_history/theme.php
index 95ead7da..9e869f24 100644
--- a/ext/tag_history/theme.php
+++ b/ext/tag_history/theme.php
@@ -15,7 +15,7 @@ class TagHistoryTheme extends Themelet
 {
     private array $messages = [];
 
-    public function display_history_page(Page $page, int $image_id, array $history)
+    public function display_history_page(Page $page, int $image_id, array $history): void
     {
         $history_html = $this->history_list($history, true);
 
@@ -25,7 +25,7 @@ class TagHistoryTheme extends Themelet
         $page->add_block(new Block("Tag History", $history_html, "main", 10));
     }
 
-    public function display_global_page(Page $page, array $history, int $page_number)
+    public function display_global_page(Page $page, array $history, int $page_number): void
     {
         $history_html = $this->history_list($history, false);
 
@@ -45,7 +45,7 @@ class TagHistoryTheme extends Themelet
     /**
      * Add a section to the admin page.
      */
-    public function display_admin_block(string $validation_msg = '')
+    public function display_admin_block(string $validation_msg = ''): void
     {
         global $page;
 
@@ -72,7 +72,7 @@ class TagHistoryTheme extends Themelet
     /*
      * Show a standard page for results to be put into
      */
-    public function display_revert_ip_results()
+    public function display_revert_ip_results(): void
     {
         global $page;
         $html = implode("\n", $this->messages);
diff --git a/ext/tag_list/theme.php b/ext/tag_list/theme.php
index d1d85ce4..1116a10a 100644
--- a/ext/tag_list/theme.php
+++ b/ext/tag_list/theme.php
@@ -26,7 +26,7 @@ class TagListTheme extends Themelet
         $this->navigation = $nav;
     }
 
-    public function display_page(Page $page)
+    public function display_page(Page $page): void
     {
         $page->set_title("Tag List");
         $page->set_heading($this->heading);
@@ -66,7 +66,7 @@ class TagListTheme extends Themelet
      *                 ...
      *              )
      */
-    public function display_split_related_block(Page $page, $tag_infos)
+    public function display_split_related_block(Page $page, $tag_infos): void
     {
         global $config;
 
@@ -162,7 +162,7 @@ class TagListTheme extends Themelet
      *                 ...
      *              )
      */
-    public function display_related_block(Page $page, $tag_infos, $block_name)
+    public function display_related_block(Page $page, $tag_infos, $block_name): void
     {
         global $config;
 
@@ -181,7 +181,7 @@ class TagListTheme extends Themelet
      *                 ...
      *              )
      */
-    public function display_popular_block(Page $page, $tag_infos)
+    public function display_popular_block(Page $page, $tag_infos): void
     {
         global $config;
 
@@ -201,7 +201,7 @@ class TagListTheme extends Themelet
      *              )
      * $search = the current array of tags being searched for
      */
-    public function display_refine_block(Page $page, $tag_infos, $search)
+    public function display_refine_block(Page $page, $tag_infos, $search): void
     {
         global $config;
 
diff --git a/ext/tag_tools/theme.php b/ext/tag_tools/theme.php
index 7cf2ea72..7a365401 100644
--- a/ext/tag_tools/theme.php
+++ b/ext/tag_tools/theme.php
@@ -28,7 +28,7 @@ class TagToolsTheme extends Themelet
      *  'recount tag use'
      *  etc
      */
-    public function display_form()
+    public function display_form(): void
     {
         global $page;
 
diff --git a/ext/update/theme.php b/ext/update/theme.php
index a990a4a7..64a640cd 100644
--- a/ext/update/theme.php
+++ b/ext/update/theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class UpdateTheme extends Themelet
 {
-    public function display_admin_block()
+    public function display_admin_block(): void
     {
         global $page, $config;
 
diff --git a/ext/user/theme.php b/ext/user/theme.php
index 3432e2aa..77996fd1 100644
--- a/ext/user/theme.php
+++ b/ext/user/theme.php
@@ -25,7 +25,7 @@ use function MicroHTML\OPTION;
 
 class UserPageTheme extends Themelet
 {
-    public function display_login_page(Page $page)
+    public function display_login_page(Page $page): void
     {
         $page->set_title("Login");
         $page->set_heading("Login");
@@ -36,7 +36,7 @@ class UserPageTheme extends Themelet
         ));
     }
 
-    public function display_user_list(Page $page, $table, $paginator)
+    public function display_user_list(Page $page, $table, $paginator): void
     {
         $page->set_title("User List");
         $page->set_heading("User List");
@@ -44,12 +44,12 @@ class UserPageTheme extends Themelet
         $page->add_block(new Block("Users", $table . $paginator));
     }
 
-    public function display_user_links(Page $page, User $user, $parts)
+    public function display_user_links(Page $page, User $user, $parts): void
     {
         # $page->add_block(new Block("User Links", join(", ", $parts), "main", 10));
     }
 
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $html = emptyHTML('Logged in as ', $user->name);
         foreach ($parts as $part) {
@@ -61,7 +61,7 @@ class UserPageTheme extends Themelet
         $page->add_block($b);
     }
 
-    public function display_signup_page(Page $page)
+    public function display_signup_page(Page $page): void
     {
         global $config, $user;
         $tac = $config->get_string("login_tac", "");
@@ -117,7 +117,7 @@ class UserPageTheme extends Themelet
         $page->add_block(new Block("Signup", $html));
     }
 
-    public function display_user_creator()
+    public function display_user_creator(): void
     {
         global $page;
 
@@ -154,7 +154,7 @@ class UserPageTheme extends Themelet
         $page->add_block(new Block("Create User", (string)$form, "main", 75));
     }
 
-    public function display_signups_disabled(Page $page)
+    public function display_signups_disabled(Page $page): void
     {
         $page->set_title("Signups Disabled");
         $page->set_heading("Signups Disabled");
@@ -165,7 +165,7 @@ class UserPageTheme extends Themelet
         ));
     }
 
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         $page->add_block(new Block("Login", $this->create_login_block(), "left", 90));
     }
@@ -218,7 +218,7 @@ class UserPageTheme extends Themelet
         return $td;
     }
 
-    public function display_ip_list(Page $page, array $uploads, array $comments, array $events)
+    public function display_ip_list(Page $page, array $uploads, array $comments, array $events): void
     {
         $html = TABLE(
             ["id" => "ip-history"],
@@ -235,7 +235,7 @@ class UserPageTheme extends Themelet
         $page->add_block(new Block("IPs", $html, "main", 70));
     }
 
-    public function display_user_page(User $duser, $stats)
+    public function display_user_page(User $duser, $stats): void
     {
         global $page;
         assert(is_array($stats));
diff --git a/ext/user_config/theme.php b/ext/user_config/theme.php
index 7d5209da..6e8593c3 100644
--- a/ext/user_config/theme.php
+++ b/ext/user_config/theme.php
@@ -39,7 +39,7 @@ class UserConfigTheme extends Themelet
      *
      * The page should wrap all the options in a form which links to setup_save
      */
-    public function display_user_config_page(Page $page, User $user, SetupPanel $panel)
+    public function display_user_config_page(Page $page, User $user, SetupPanel $panel): void
     {
         usort($panel->blocks, "Shimmie2\blockcmp");
 
diff --git a/ext/view/theme.php b/ext/view/theme.php
index 84efbf01..c38ca4c6 100644
--- a/ext/view/theme.php
+++ b/ext/view/theme.php
@@ -10,7 +10,7 @@ use function MicroHTML\{A, joinHTML, TABLE, TR, TD, INPUT, emptyHTML};
 
 class ViewPostTheme extends Themelet
 {
-    public function display_meta_headers(Image $image)
+    public function display_meta_headers(Image $image): void
     {
         global $page;
 
@@ -25,7 +25,7 @@ class ViewPostTheme extends Themelet
     /*
      * Build a page showing $image and some info about it
      */
-    public function display_page(Image $image, $editor_parts)
+    public function display_page(Image $image, $editor_parts): void
     {
         global $page;
         $page->set_title("Post {$image->id}: ".$image->get_tag_list());
@@ -41,7 +41,7 @@ class ViewPostTheme extends Themelet
         }
     }
 
-    public function display_admin_block(Page $page, $parts)
+    public function display_admin_block(Page $page, $parts): void
     {
         if (count($parts) > 0) {
             $page->add_block(new Block("Post Controls", join("<br>", $parts), "left", 50));
diff --git a/ext/wiki/theme.php b/ext/wiki/theme.php
index 2d4dfd02..861ed4aa 100644
--- a/ext/wiki/theme.php
+++ b/ext/wiki/theme.php
@@ -12,7 +12,7 @@ class WikiTheme extends Themelet
      * $wiki_page The wiki page, has ->title and ->body
      * $nav_page A wiki page object with navigation, has ->body
      */
-    public function display_page(Page $page, WikiPage $wiki_page, ?WikiPage $nav_page = null)
+    public function display_page(Page $page, WikiPage $wiki_page, ?WikiPage $nav_page = null): void
     {
         global $user;
 
@@ -47,7 +47,7 @@ class WikiTheme extends Themelet
         $page->add_block(new Block($title_html, $this->create_display_html($wiki_page)));
     }
 
-    public function display_page_history(Page $page, string $title, array $history)
+    public function display_page_history(Page $page, string $title, array $history): void
     {
         $html = "<table class='zebra'>";
         foreach ($history as $row) {
@@ -61,7 +61,7 @@ class WikiTheme extends Themelet
         $page->add_block(new Block(html_escape($title), $html));
     }
 
-    public function display_page_editor(Page $page, WikiPage $wiki_page)
+    public function display_page_editor(Page $page, WikiPage $wiki_page): void
     {
         $page->set_title(html_escape($wiki_page->title));
         $page->set_heading(html_escape($wiki_page->title));
diff --git a/themes/danbooru/comment.theme.php b/themes/danbooru/comment.theme.php
index 935a560c..3249679d 100644
--- a/themes/danbooru/comment.theme.php
+++ b/themes/danbooru/comment.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomCommentListTheme extends CommentListTheme
 {
-    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post)
+    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post): void
     {
         global $config, $page, $user;
 
@@ -85,7 +85,7 @@ class CustomCommentListTheme extends CommentListTheme
         }
     }
 
-    public function display_recent_comments(array $comments)
+    public function display_recent_comments(array $comments): void
     {
         // no recent comments in this theme
     }
diff --git a/themes/danbooru/index.theme.php b/themes/danbooru/index.theme.php
index 8dd0aa9c..80f00517 100644
--- a/themes/danbooru/index.theme.php
+++ b/themes/danbooru/index.theme.php
@@ -9,7 +9,7 @@ class CustomIndexTheme extends IndexTheme
     /**
      * @param Image[] $images
      */
-    public function display_page(Page $page, array $images)
+    public function display_page(Page $page, array $images): void
     {
         $this->display_shortwiki($page);
 
diff --git a/themes/danbooru/tag_list.theme.php b/themes/danbooru/tag_list.theme.php
index 4dd0bb02..118019e0 100644
--- a/themes/danbooru/tag_list.theme.php
+++ b/themes/danbooru/tag_list.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomTagListTheme extends TagListTheme
 {
-    public function display_page(Page $page)
+    public function display_page(Page $page): void
     {
         $page->disable_left();
         parent::display_page($page);
diff --git a/themes/danbooru/themelet.class.php b/themes/danbooru/themelet.class.php
index 4b7a1a2a..422c62ec 100644
--- a/themes/danbooru/themelet.class.php
+++ b/themes/danbooru/themelet.class.php
@@ -10,7 +10,7 @@ use function MicroHTML\{A, B, DIV, joinHTML};
 
 class Themelet extends BaseThemelet
 {
-    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false)
+    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false): void
     {
         if ($total_pages == 0) {
             $total_pages = 1;
diff --git a/themes/danbooru/user.theme.php b/themes/danbooru/user.theme.php
index 276dd53f..a78bbde2 100644
--- a/themes/danbooru/user.theme.php
+++ b/themes/danbooru/user.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomUserPageTheme extends UserPageTheme
 {
-    public function display_login_page(Page $page)
+    public function display_login_page(Page $page): void
     {
         global $config;
         $page->set_title("Login");
@@ -33,16 +33,16 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Login", $html, "main", 90));
     }
 
-    public function display_user_links(Page $page, User $user, $parts)
+    public function display_user_links(Page $page, User $user, $parts): void
     {
         // no block in this theme
     }
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         // no block in this theme
     }
 
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $html = "";
         $blocked = ["Pools", "Pool Changes", "Alias Editor", "My Profile"];
@@ -57,7 +57,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block($b);
     }
 
-    public function display_signup_page(Page $page)
+    public function display_signup_page(Page $page): void
     {
         global $config;
         $tac = $config->get_string("login_tac", "");
@@ -91,7 +91,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Signup", $html));
     }
 
-    public function display_ip_list(Page $page, array $uploads, array $comments, array $events)
+    public function display_ip_list(Page $page, array $uploads, array $comments, array $events): void
     {
         $html = "<table id='ip-history' style='width: 400px;'>";
         $html .= "<tr><td>Uploaded from: ";
@@ -108,7 +108,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("IPs", $html));
     }
 
-    public function display_user_page(User $duser, $stats)
+    public function display_user_page(User $duser, $stats): void
     {
         global $page;
         $page->disable_left();
diff --git a/themes/danbooru/view.theme.php b/themes/danbooru/view.theme.php
index 121a93dc..1fc77387 100644
--- a/themes/danbooru/view.theme.php
+++ b/themes/danbooru/view.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomViewPostTheme extends ViewPostTheme
 {
-    public function display_page(Image $image, $editor_parts)
+    public function display_page(Image $image, $editor_parts): void
     {
         global $page;
         $page->set_heading(html_escape($image->get_tag_list()));
diff --git a/themes/danbooru2/admin.theme.php b/themes/danbooru2/admin.theme.php
index 1d8082f6..56393863 100644
--- a/themes/danbooru2/admin.theme.php
+++ b/themes/danbooru2/admin.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomAdminPageTheme extends AdminPageTheme
 {
-    public function display_page()
+    public function display_page(): void
     {
         global $page;
         $page->disable_left();
diff --git a/themes/danbooru2/comment.theme.php b/themes/danbooru2/comment.theme.php
index 4ca014e9..d94709ee 100644
--- a/themes/danbooru2/comment.theme.php
+++ b/themes/danbooru2/comment.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomCommentListTheme extends CommentListTheme
 {
-    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post)
+    public function display_comment_list(array $images, int $page_number, int $total_pages, bool $can_post): void
     {
         global $config, $page, $user;
 
@@ -85,7 +85,7 @@ class CustomCommentListTheme extends CommentListTheme
         }
     }
 
-    public function display_recent_comments(array $comments)
+    public function display_recent_comments(array $comments): void
     {
         // no recent comments in this theme
     }
diff --git a/themes/danbooru2/ext_manager.theme.php b/themes/danbooru2/ext_manager.theme.php
index bdc7b0c2..1d283157 100644
--- a/themes/danbooru2/ext_manager.theme.php
+++ b/themes/danbooru2/ext_manager.theme.php
@@ -6,13 +6,13 @@ namespace Shimmie2;
 
 class CustomExtManagerTheme extends ExtManagerTheme
 {
-    public function display_table(Page $page, array $extensions, bool $editable)
+    public function display_table(Page $page, array $extensions, bool $editable): void
     {
         $page->disable_left();
         parent::display_table($page, $extensions, $editable);
     }
 
-    public function display_doc(Page $page, ExtensionInfo $info)
+    public function display_doc(Page $page, ExtensionInfo $info): void
     {
         $page->disable_left();
         parent::display_doc($page, $info);
diff --git a/themes/danbooru2/index.theme.php b/themes/danbooru2/index.theme.php
index e1fa8aa4..6f7d9808 100644
--- a/themes/danbooru2/index.theme.php
+++ b/themes/danbooru2/index.theme.php
@@ -9,7 +9,7 @@ class CustomIndexTheme extends IndexTheme
     /**
      * @param Image[] $images
      */
-    public function display_page(Page $page, array $images)
+    public function display_page(Page $page, array $images): void
     {
         $this->display_shortwiki($page);
 
diff --git a/themes/danbooru2/tag_list.theme.php b/themes/danbooru2/tag_list.theme.php
index 4dd0bb02..118019e0 100644
--- a/themes/danbooru2/tag_list.theme.php
+++ b/themes/danbooru2/tag_list.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomTagListTheme extends TagListTheme
 {
-    public function display_page(Page $page)
+    public function display_page(Page $page): void
     {
         $page->disable_left();
         parent::display_page($page);
diff --git a/themes/danbooru2/themelet.class.php b/themes/danbooru2/themelet.class.php
index 7e619442..5f810471 100644
--- a/themes/danbooru2/themelet.class.php
+++ b/themes/danbooru2/themelet.class.php
@@ -10,7 +10,7 @@ use function MicroHTML\{A,B,DIV,joinHTML};
 
 class Themelet extends BaseThemelet
 {
-    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false)
+    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false): void
     {
         if ($total_pages == 0) {
             $total_pages = 1;
diff --git a/themes/danbooru2/user.theme.php b/themes/danbooru2/user.theme.php
index 276dd53f..a78bbde2 100644
--- a/themes/danbooru2/user.theme.php
+++ b/themes/danbooru2/user.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomUserPageTheme extends UserPageTheme
 {
-    public function display_login_page(Page $page)
+    public function display_login_page(Page $page): void
     {
         global $config;
         $page->set_title("Login");
@@ -33,16 +33,16 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Login", $html, "main", 90));
     }
 
-    public function display_user_links(Page $page, User $user, $parts)
+    public function display_user_links(Page $page, User $user, $parts): void
     {
         // no block in this theme
     }
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         // no block in this theme
     }
 
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $html = "";
         $blocked = ["Pools", "Pool Changes", "Alias Editor", "My Profile"];
@@ -57,7 +57,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block($b);
     }
 
-    public function display_signup_page(Page $page)
+    public function display_signup_page(Page $page): void
     {
         global $config;
         $tac = $config->get_string("login_tac", "");
@@ -91,7 +91,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Signup", $html));
     }
 
-    public function display_ip_list(Page $page, array $uploads, array $comments, array $events)
+    public function display_ip_list(Page $page, array $uploads, array $comments, array $events): void
     {
         $html = "<table id='ip-history' style='width: 400px;'>";
         $html .= "<tr><td>Uploaded from: ";
@@ -108,7 +108,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("IPs", $html));
     }
 
-    public function display_user_page(User $duser, $stats)
+    public function display_user_page(User $duser, $stats): void
     {
         global $page;
         $page->disable_left();
diff --git a/themes/danbooru2/view.theme.php b/themes/danbooru2/view.theme.php
index bfc44db0..3141f41e 100644
--- a/themes/danbooru2/view.theme.php
+++ b/themes/danbooru2/view.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomViewPostTheme extends ViewPostTheme
 {
-    public function display_page(Image $image, $editor_parts)
+    public function display_page(Image $image, $editor_parts): void
     {
         global $page;
         $page->set_heading(html_escape($image->get_tag_list()));
diff --git a/themes/futaba/themelet.class.php b/themes/futaba/themelet.class.php
index e059b3c2..1c0f53e6 100644
--- a/themes/futaba/themelet.class.php
+++ b/themes/futaba/themelet.class.php
@@ -9,7 +9,7 @@ class Themelet extends BaseThemelet
     /**
      * Add a generic paginator.
      */
-    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false)
+    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false): void
     {
         if ($total_pages == 0) {
             $total_pages = 1;
diff --git a/themes/futaba/view.theme.php b/themes/futaba/view.theme.php
index 7f4a9f19..6370969c 100644
--- a/themes/futaba/view.theme.php
+++ b/themes/futaba/view.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomViewPostTheme extends ViewPostTheme
 {
-    public function display_page(Image $image, $editor_parts)
+    public function display_page(Image $image, $editor_parts): void
     {
         global $page;
         $page->set_heading(html_escape($image->get_tag_list()));
diff --git a/themes/lite/themelet.class.php b/themes/lite/themelet.class.php
index fd293a38..1717e769 100644
--- a/themes/lite/themelet.class.php
+++ b/themes/lite/themelet.class.php
@@ -10,7 +10,7 @@ use function MicroHTML\{A,DIV,SPAN,joinHTML};
 
 class Themelet extends BaseThemelet
 {
-    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false)
+    public function display_paginator(Page $page, string $base, ?string $query, int $page_number, int $total_pages, bool $show_random = false): void
     {
         if ($total_pages == 0) {
             $total_pages = 1;
diff --git a/themes/lite/user.theme.php b/themes/lite/user.theme.php
index 14327f6d..5ac89f24 100644
--- a/themes/lite/user.theme.php
+++ b/themes/lite/user.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomUserPageTheme extends UserPageTheme
 {
-    public function display_login_page(Page $page)
+    public function display_login_page(Page $page): void
     {
         global $config;
         $page->set_title("Login");
@@ -33,16 +33,16 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Login", $html, "main", 90));
     }
 
-    public function display_user_links(Page $page, User $user, $parts)
+    public function display_user_links(Page $page, User $user, $parts): void
     {
         // no block in this theme
     }
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         // no block in this theme
     }
 
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $html = "";
         $blocked = ["Pools", "Pool Changes", "Alias Editor", "My Profile"];
@@ -57,13 +57,13 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block($b);
     }
 
-    public function display_signup_page(Page $page)
+    public function display_signup_page(Page $page): void
     {
         $page->disable_left();
         parent::display_signup_page($page);
     }
 
-    public function display_ip_list(Page $page, array $uploads, array $comments, array $events)
+    public function display_ip_list(Page $page, array $uploads, array $comments, array $events): void
     {
         $html = "<table id='ip-history' style='width: 400px;'>";
         $html .= "<tr><td>Uploaded from: ";
@@ -80,7 +80,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("IPs", $html));
     }
 
-    public function display_user_page(User $duser, $stats)
+    public function display_user_page(User $duser, $stats): void
     {
         global $page;
         $page->disable_left();
diff --git a/themes/lite/view.theme.php b/themes/lite/view.theme.php
index 7b0f018b..b887ab7d 100644
--- a/themes/lite/view.theme.php
+++ b/themes/lite/view.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomViewPostTheme extends ViewPostTheme
 {
-    public function display_page(Image $image, $editor_parts)
+    public function display_page(Image $image, $editor_parts): void
     {
         global $page;
         $page->set_title("Post {$image->id}: ".$image->get_tag_list());
diff --git a/themes/rule34v2/index.theme.php b/themes/rule34v2/index.theme.php
index 1ac3b8ac..ebbaf1f8 100644
--- a/themes/rule34v2/index.theme.php
+++ b/themes/rule34v2/index.theme.php
@@ -26,7 +26,7 @@ class CustomIndexTheme extends IndexTheme
     }
 
     // Override to add a custom error message
-    public function display_page(Page $page, $images)
+    public function display_page(Page $page, $images): void
     {
         $this->display_page_header($page, $images);
 
diff --git a/themes/rule34v2/user.theme.php b/themes/rule34v2/user.theme.php
index 600d90d6..eee5257d 100644
--- a/themes/rule34v2/user.theme.php
+++ b/themes/rule34v2/user.theme.php
@@ -27,7 +27,7 @@ class CustomUserPageTheme extends UserPageTheme
     // (with css media queries deciding which one is visible), and also
     // to switch between new-line and inline display depending on the
     // number of links.
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $h_name = html_escape($user->name);
         $lines = [];
@@ -48,7 +48,7 @@ class CustomUserPageTheme extends UserPageTheme
 
     // Override to display login block in the head and in the left column
     // (with css media queries deciding which one is visible)
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         $page->add_block(new Block("Login", $this->create_login_block(), "head", 90));
         $page->add_block(new Block("Login", $this->create_login_block(), "left", 15));
diff --git a/themes/warm/user.theme.php b/themes/warm/user.theme.php
index a58e9ceb..7904a34e 100644
--- a/themes/warm/user.theme.php
+++ b/themes/warm/user.theme.php
@@ -6,7 +6,7 @@ namespace Shimmie2;
 
 class CustomUserPageTheme extends UserPageTheme
 {
-    public function display_user_block(Page $page, User $user, $parts)
+    public function display_user_block(Page $page, User $user, $parts): void
     {
         $h_name = html_escape($user->name);
         $html = " | ";
@@ -16,7 +16,7 @@ class CustomUserPageTheme extends UserPageTheme
         $page->add_block(new Block("Logged in as $h_name", $html, "head", 90));
     }
 
-    public function display_login_block(Page $page)
+    public function display_login_block(Page $page): void
     {
         global $config;
         $html = "