diff --git a/core/basepage.php b/core/basepage.php
index 3bd5f550..e3fb982c 100644
--- a/core/basepage.php
+++ b/core/basepage.php
@@ -298,7 +298,7 @@ class BasePage
 
                 if (isset($_SERVER['HTTP_RANGE'])) {
                     list(, $range) = explode('=', $_SERVER['HTTP_RANGE'], 2);
-                    if (strpos($range, ',') !== false) {
+                    if (str_contains($range, ',')) {
                         header('HTTP/1.1 416 Requested Range Not Satisfiable');
                         header("Content-Range: bytes $start-$end/$size");
                         break;
@@ -335,7 +335,7 @@ class BasePage
                 break;
             case PageMode::REDIRECT:
                 if ($this->flash) {
-                    $this->redirect .= (strpos($this->redirect, "?") === false) ? "?" : "&";
+                    $this->redirect .= str_contains($this->redirect, "?") ? "&" : "?";
                     $this->redirect .= "flash=" . url_escape(implode("\n", $this->flash));
                 }
                 header('Location: ' . $this->redirect);
diff --git a/core/extension.php b/core/extension.php
index 54074b13..6409267e 100644
--- a/core/extension.php
+++ b/core/extension.php
@@ -413,7 +413,7 @@ abstract class DataHandlerExtension extends Extension
 
         $image->filesize = $metadata['size'];
         $image->hash = $metadata['hash'];
-        $image->filename = (($pos = strpos($metadata['filename'], '?')) !== false) ? substr($metadata['filename'], 0, $pos) : $metadata['filename'];
+        $image->filename = ($pos = str_contains($metadata['filename'], '?')) ? substr($metadata['filename'], 0, $pos) : $metadata['filename'];
 
         if (array_key_exists("extension", $metadata)) {
             $image->set_mime(MimeType::get_for_file($filename, $metadata["extension"]));
diff --git a/core/imageboard/image.php b/core/imageboard/image.php
index a958403e..e5f2b156 100644
--- a/core/imageboard/image.php
+++ b/core/imageboard/image.php
@@ -533,7 +533,7 @@ class Image
         $image_link = $config->get_string($template);
 
         if (!empty($image_link)) {
-            if (!(strpos($image_link, "://") > 0) && !str_starts_with($image_link, "/")) {
+            if (!str_contains($image_link, "://") && !str_starts_with($image_link, "/")) {
                 $image_link = make_link($image_link);
             }
             $chosen = $image_link;
diff --git a/core/polyfills.php b/core/polyfills.php
index 1bdf0d7b..04d0e793 100644
--- a/core/polyfills.php
+++ b/core/polyfills.php
@@ -345,15 +345,21 @@ function unparse_url($parsed_url)
 if (!function_exists('str_starts_with')) {
     function str_starts_with(string $haystack, string $needle): bool
     {
-        $length = strlen($needle);
-        return (substr($haystack, 0, $length) === $needle);
+        return \strncmp($haystack, $needle, \strlen($needle)) === 0;
     }
+}
 
+if (!function_exists('str_ends_with')) {
     function str_ends_with(string $haystack, string $needle): bool
     {
-        $length = strlen($needle);
-        $start = $length * -1; //negative
-        return (substr($haystack, $start) === $needle);
+        return $needle === '' || $needle === \substr($haystack, - \strlen($needle));
+    }
+}
+
+if (!function_exists('str_contains')) {
+    function str_contains(string $haystack, string $needle): bool
+    {
+        return '' === $needle || false !== strpos($haystack, $needle);
     }
 }
 
diff --git a/core/sanitize_php.php b/core/sanitize_php.php
index 5f36cddb..56e44b34 100644
--- a/core/sanitize_php.php
+++ b/core/sanitize_php.php
@@ -42,7 +42,7 @@ ini_set('assert.exception', '1');  // throw exceptions when failed
 set_error_handler(function ($errNo, $errStr) {
     // Should we turn ALL notices into errors? PHP allows a lot of
     // terrible things to happen by default...
-    if (strpos($errStr, 'Use of undefined constant ') === 0) {
+    if (str_starts_with($errStr, 'Use of undefined constant ')) {
         throw new Exception("PHP Error#$errNo: $errStr");
     } else {
         return false;
diff --git a/core/urls.php b/core/urls.php
index 1dd6a7ca..1ca3192d 100644
--- a/core/urls.php
+++ b/core/urls.php
@@ -79,7 +79,7 @@ function modify_url(string $url, array $changes): string
  */
 function make_http(string $link): string
 {
-    if (strpos($link, "://") > 0) {
+    if (str_contains($link, "://")) {
         return $link;
     }
 
@@ -105,7 +105,7 @@ function referer_or(string $dest, ?array $blacklist=null): string
     }
     if ($blacklist) {
         foreach ($blacklist as $b) {
-            if (strstr($_SERVER['HTTP_REFERER'], $b)) {
+            if (str_contains($_SERVER['HTTP_REFERER'], $b)) {
                 return $dest;
             }
         }
diff --git a/core/user.php b/core/user.php
index 1496c208..c1ddf9e8 100644
--- a/core/user.php
+++ b/core/user.php
@@ -118,7 +118,7 @@ class User
         $my_user = User::by_name($name);
 
         // If user tried to log in as "foo bar" and failed, try "foo_bar"
-        if (!$my_user && strpos($name, " ") !== false) {
+        if (!$my_user && str_contains($name, " ")) {
             $my_user = User::by_name(str_replace(" ", "_", $name));
         }
 
diff --git a/core/util.php b/core/util.php
index d9b197a3..23149cdf 100644
--- a/core/util.php
+++ b/core/util.php
@@ -53,11 +53,11 @@ function contact_link(): ?string
         return $text;
     }
 
-    if (strpos($text, "@")) {
+    if (str_contains($text, "@")) {
         return "mailto:$text";
     }
 
-    if (strpos($text, "/")) {
+    if (str_contains($text, "/")) {
         return "http://$text";
     }
 
@@ -348,7 +348,7 @@ function path_to_tags(string $path): string
                 // which is for inheriting to tags on the subfolder
                 $category_to_inherit = $tag;
             } else {
-                if ($category!=""&&strpos($tag, ":") === false) {
+                if ($category!="" && !str_contains($tag, ":")) {
                     // This indicates that category inheritance is active,
                     // and we've encountered a tag that does not specify a category.
                     // So we attach the inherited category to the tag.
diff --git a/ext/artists/main.php b/ext/artists/main.php
index df49771a..77f2de0d 100644
--- a/ext/artists/main.php
+++ b/ext/artists/main.php
@@ -553,7 +553,7 @@ class Artists extends Extension
         $urlsAsString = $inputs["urls"];
         $urlsIDsAsString = $inputs["urlsIDs"];
 
-        if (strpos($name, " ")) {
+        if (str_contains($name, " ")) {
             return;
         }
 
@@ -695,7 +695,7 @@ class Artists extends Extension
         ]);
 
         $name = $inputs["name"];
-        if (strpos($name, " ")) {
+        if (str_contains($name, " ")) {
             return -1;
         }
 
diff --git a/ext/ban_words/main.php b/ext/ban_words/main.php
index 44a9f48e..3ed7d253 100644
--- a/ext/ban_words/main.php
+++ b/ext/ban_words/main.php
@@ -87,7 +87,7 @@ xanax
                 }
             } else {
                 // other words are literal
-                if (strpos($comment, $word) !== false) {
+                if (str_contains($comment, $word)) {
                     throw $ex;
                 }
             }
diff --git a/ext/bulk_actions/main.php b/ext/bulk_actions/main.php
index 35455f48..a81adb31 100644
--- a/ext/bulk_actions/main.php
+++ b/ext/bulk_actions/main.php
@@ -255,7 +255,7 @@ class BulkActions extends Extension
         $pos_tag_array = [];
         $neg_tag_array = [];
         foreach ($tags as $new_tag) {
-            if (strpos($new_tag, '-') === 0) {
+            if (str_starts_with($new_tag, '-')) {
                 $neg_tag_array[] = substr($new_tag, 1);
             } else {
                 $pos_tag_array[] = $new_tag;
diff --git a/ext/custom_html_headers/main.php b/ext/custom_html_headers/main.php
index ffeb938e..52a09687 100644
--- a/ext/custom_html_headers/main.php
+++ b/ext/custom_html_headers/main.php
@@ -55,7 +55,7 @@ class CustomHtmlHeaders extends Extension
         $sitename_in_title = $config->get_string("sitename_in_title");
 
         // sitename is already in title (can occur on index & other pages)
-        if (strstr($page->title, $site_title)) {
+        if (str_contains($page->title, $site_title)) {
             return;
         }
 
diff --git a/ext/handle_cbz/main.php b/ext/handle_cbz/main.php
index eaf7503d..40e6e4c5 100644
--- a/ext/handle_cbz/main.php
+++ b/ext/handle_cbz/main.php
@@ -55,7 +55,7 @@ class CBZFileHandler extends DataHandlerExtension
         sort($names);
         $cover = $names[0];
         foreach ($names as $name) {
-            if (strpos(strtolower($name), "cover") !== false) {
+            if (str_contains(strtolower($name), "cover")) {
                 $cover = $name;
                 break;
             }
diff --git a/ext/image/main.php b/ext/image/main.php
index a7e3812d..c5b0902b 100644
--- a/ext/image/main.php
+++ b/ext/image/main.php
@@ -301,7 +301,7 @@ class ImageIO extends Extension
     public function onParseLinkTemplate(ParseLinkTemplateEvent $event)
     {
         $fname = $event->image->get_filename();
-        $base_fname = strpos($fname, '.') ? substr($fname, 0, strrpos($fname, '.')) : $fname;
+        $base_fname = str_contains($fname, '.') ? substr($fname, 0, strrpos($fname, '.')) : $fname;
 
         $event->replace('$id', (string)$event->image->id);
         $event->replace('$hash_ab', substr($event->image->hash, 0, 2));
diff --git a/ext/index/main.php b/ext/index/main.php
index b0a30c81..d85da537 100644
--- a/ext/index/main.php
+++ b/ext/index/main.php
@@ -46,10 +46,10 @@ class Index extends Extension
                 if (
                     SPEED_HAX
                     && (
-                        strstr($ua, "Googlebot") !== false
-                        || strstr($ua, "YandexBot") !== false
-                        || strstr($ua, "bingbot") !== false
-                        || strstr($ua, "msnbot") !== false
+                        str_contains($ua, "Googlebot")
+                        || str_contains($ua, "YandexBot")
+                        || str_contains($ua, "bingbot")
+                        || str_contains($ua, "msnbot")
                     )
                     && (
                         $count_search_terms > 1
diff --git a/ext/ipban/main.php b/ext/ipban/main.php
index 7dd8c337..633f1acf 100644
--- a/ext/ipban/main.php
+++ b/ext/ipban/main.php
@@ -113,7 +113,7 @@ class IPBan extends Extension
             $ips = []; # "0.0.0.0" => 123;
             $networks = []; # "0.0.0.0/32" => 456;
             foreach ($rows as $ip => $id) {
-                if (strstr($ip, '/')) {
+                if (str_contains($ip, '/')) {
                     $networks[$ip] = $id;
                 } else {
                     $ips[$ip] = $id;
diff --git a/ext/rule34/main.php b/ext/rule34/main.php
index baa14f74..ffb466e9 100644
--- a/ext/rule34/main.php
+++ b/ext/rule34/main.php
@@ -7,8 +7,8 @@ use function MicroHTML\A;
 
 if ( // kill these glitched requests immediately
     !empty($_SERVER["REQUEST_URI"])
-    && strpos(@$_SERVER["REQUEST_URI"], "/http") !== false
-    && strpos(@$_SERVER["REQUEST_URI"], "paheal.net") !== false
+    && str_contains(@$_SERVER["REQUEST_URI"], "/http")
+    && str_contains(@$_SERVER["REQUEST_URI"], "paheal.net")
 ) {
     die("No");
 }
diff --git a/ext/setup/theme.php b/ext/setup/theme.php
index f19a6b83..71aa0d9f 100644
--- a/ext/setup/theme.php
+++ b/ext/setup/theme.php
@@ -52,7 +52,7 @@ class SetupTheme extends Themelet
             $h_value = html_escape((string)$value);
 
             $h_box = "";
-            if (is_string($value) && strpos($value, "\n") > 0) {
+            if (is_string($value) && str_contains($value, "\n")) {
                 $h_box .= "<textarea cols='50' rows='4' name='_config_$h_name'>$h_value</textarea>";
             } else {
                 $h_box .= "<input type='text' name='_config_$h_name' value='$h_value'>";
diff --git a/ext/tag_edit/main.php b/ext/tag_edit/main.php
index a080da62..4613c357 100644
--- a/ext/tag_edit/main.php
+++ b/ext/tag_edit/main.php
@@ -68,7 +68,7 @@ class TagSetEvent extends Event
         $this->metatags = [];
 
         foreach ($tags as $tag) {
-            if ((strpos($tag, ':') === false) && (strpos($tag, '=') === false)) {
+            if ((!str_contains($tag, ':')) && (!str_contains($tag, '='))) {
                 //Tag doesn't contain : or =, meaning it can't possibly be a metatag.
                 //This should help speed wise, as it avoids running every single tag through a bunch of preg_match instead.
                 array_push($this->tags, $tag);
diff --git a/ext/tag_list/main.php b/ext/tag_list/main.php
index be669b33..7ff990c5 100644
--- a/ext/tag_list/main.php
+++ b/ext/tag_list/main.php
@@ -198,8 +198,8 @@ class TagList extends Extension
                 $i++;
                 $arg = "tag$i";
                 $args[$arg] = Tag::sqlify($tag);
-                if (strpos($tag, '*') === false
-                    && strpos($tag, '?') === false) {
+                if (!str_contains($tag, '*')
+                    && !str_contains($tag, '?')) {
                     $where[] = " tag = :$arg ";
                 } else {
                     $where[] = " tag LIKE :$arg ";
@@ -587,7 +587,7 @@ class TagList extends Extension
             $starting_tags = [];
             $tags_ok = true;
             foreach ($wild_tags as $tag) {
-                if ($tag[0] == "-" || strpos($tag, "tagme")===0) {
+                if ($tag[0] == "-" || str_starts_with($tag, "tagme")) {
                     continue;
                 }
                 $tag = Tag::sqlify($tag);
diff --git a/ext/upload/theme.php b/ext/upload/theme.php
index 10d4bcc2..8f476bd1 100644
--- a/ext/upload/theme.php
+++ b/ext/upload/theme.php
@@ -205,7 +205,7 @@ class UploadTheme extends Themelet
     public function display_upload_error(Page $page, string $title, string $message)
     {
         // this message has intentional HTML in it...
-        $message = strpos($message, "already has hash") ? $message : html_escape($message);
+        $message = str_contains($message, "already has hash") ? $message : html_escape($message);
         $page->add_block(new Block($title, $message));
     }