diff --git a/inc/functions/mime.php b/inc/functions/mime.php
new file mode 100644
index 00000000..233beec8
--- /dev/null
+++ b/inc/functions/mime.php
@@ -0,0 +1,36 @@
+<?php
+namespace Vichan\Functions\Mime;
+
+
+/**
+ * @param string $mime Lowercase valid mime type.
+ * @return ?string Vichan's preferred extension for the given mime type, if any.
+ */
+function mime_to_ext(string $mime): ?string {
+	static $mime_to_ext = [
+		'image/jpeg' => 'jpg',
+		'image/png' => 'png',
+		'image/gif' => 'gif',
+		'image/webp' => 'webp',
+		'image/bmp' => 'bmp',
+		'image/avif' => 'avif'
+	];
+	return $mime_to_ext[$mime] ?? null;
+}
+
+/**
+ * @param string $mime Lowercase extension.
+ * @return ?string Vichan's preferred mime type for the given extensions, if any.
+ */
+function ext_to_mime(string $ext): ?string {
+	static $ext_to_mime = [
+		'jpg' => 'image/jpeg',
+		'jpeg' => 'image/jpeg',
+		'png' => 'image/png',
+		'gif' => 'image/gif',
+		'webp' => 'image/webp',
+		'bmp' => 'image/bmp',
+		'avif' => 'image/avif',
+	];
+	return $ext_to_mime[$ext] ?? null;
+}