diff --git a/php/generate-preview.php b/php/generate-preview.php
new file mode 100644
index 0000000..88f17f7
--- /dev/null
+++ b/php/generate-preview.php
@@ -0,0 +1,49 @@
+<?php
+
+function generate_preview ($icon_path, $preview_path) {
+	$image = new Imagick();
+	$image->setBackgroundColor(new ImagickPixel('#ffffff'));
+	$image->readImageBlob(file_get_contents($icon_path));
+	$image->setImageFormat("png24");
+	$image->setImageInterpolateMethod(Imagick::INTERPOLATE_INTEGER);
+	$image->resizeImage(180, 180, Imagick::FILTER_POINT, 1);
+	$image->borderImage('#ffffff', 510, 225);
+	$image->writeImage($preview_path);
+}
+
+$current_icon = false;
+if (isset($argv[1])) {
+	$current_icon = $argv[1];
+} elseif (isset($_GET['icon'])) {
+	$current_icon = $_GET['icon'];
+}
+
+$icon_dir = __DIR__."/icons";
+$preview_dir = __DIR__."/preview";
+
+if ($current_icon) {
+	$icon_path = "$icon_dir/$current_icon.svg";
+	$preview_path = "$preview_dir/$current_icon.png";
+	generate_preview($icon_path, $preview_path);
+} else {
+	// no icon specified, generate all
+
+	$icon_json = json_decode(file_get_contents(__DIR__ . "/assets/icons.json"), true);
+
+	foreach ($icon_json as $filename => $tags) {
+		$icon_name = str_replace(".svg", "", $filename);
+		$icon_path = "$icon_dir/$filename";
+		$preview_path = "$preview_dir/$icon_name.png";
+
+		if (is_file($preview_path) && filemtime($preview_path) > filemtime($icon_path)) {
+			continue;
+		}
+
+		generate_preview($icon_path, $preview_path);
+	}
+
+	$file = fopen(__DIR__ . "/last_generate", "w");
+	fwrite($file, time());
+	fclose($file);
+}
+
diff --git a/php/icon.php b/php/icon.php
index 4cfe671..6a7b499 100644
--- a/php/icon.php
+++ b/php/icon.php
@@ -17,15 +17,8 @@ if (!is_file($icon_path)) {
 }
 
 // generate facebook preview
-if (!is_file($preview_path)) {
-	$image = new Imagick();
-	$image->setBackgroundColor(new ImagickPixel('#ffffff'));
-	$image->readImageBlob(file_get_contents($icon_path));
-	$image->setImageFormat("png24");
-	$image->setImageInterpolateMethod(Imagick::INTERPOLATE_INTEGER);
-	$image->resizeImage(180, 180, Imagick::FILTER_POINT, 1);
-	$image->borderImage('#ffffff', 510, 225);
-	$image->writeImage($preview_path);
+if (!is_file($preview_path) || filemtime($preview_path) < filemtime($icon_path)) {
+	require_once(__DIR__ . "/generate-preview.php");
 	$preview_mtime = time();
 } else {
 	$preview_mtime = filemtime($preview_path);
diff --git a/php/index.php b/php/index.php
index eb86c92..07e364b 100644
--- a/php/index.php
+++ b/php/index.php
@@ -102,4 +102,14 @@ $files = array_map(function ($file) {
 			})()
 		</script>
 	</body>
-</html>
\ No newline at end of file
+</html>
+<?php
+
+$last_generate = 0;
+if (is_file(__DIR__ . "/last_generate")) {
+	$last_generate = file_get_contents(__DIR__ . "/last_generate");
+}
+
+if ($last_generate < filemtime(__DIR__ . "/assets/icons.json")) {
+	shell_exec('php "' . __DIR__ . '/generate-preview.php" > /dev/null 2>&1 &');
+}
\ No newline at end of file