diff --git a/src/note.ts b/src/note.ts
index 7dc39f5a..71dc0174 100644
--- a/src/note.ts
+++ b/src/note.ts
@@ -1,10 +1,10 @@
-import { typeByExtension } from '@std/media-types';
 import 'linkify-plugin-hashtag';
 import linkifyStr from 'linkify-string';
 import linkify from 'linkifyjs';
 import { nip19, nip21 } from 'nostr-tools';
 
 import { Conf } from '@/config.ts';
+import { getUrlMediaType, isPermittedMediaType } from '@/utils/media.ts';
 import { type DittoAttachment } from '@/views/mastodon/attachments.ts';
 
 linkify.registerCustomProtocol('nostr', true);
@@ -60,16 +60,14 @@ function parseNoteContent(content: string): ParsedNoteContent {
 
 function getMediaLinks(links: Link[]): DittoAttachment[] {
   return links.reduce<DittoAttachment[]>((acc, link) => {
-    const mimeType = getUrlMimeType(link.href);
-    if (!mimeType) return acc;
+    const mediaType = getUrlMediaType(link.href);
+    if (!mediaType) return acc;
 
-    const [baseType, _subType] = mimeType.split('/');
-
-    if (['audio', 'image', 'video'].includes(baseType)) {
+    if (isPermittedMediaType(mediaType, ['audio', 'image', 'video'])) {
       acc.push({
         url: link.href,
         data: {
-          mime: mimeType,
+          mime: mediaType,
         },
       });
     }
@@ -79,7 +77,7 @@ function getMediaLinks(links: Link[]): DittoAttachment[] {
 }
 
 function isNonMediaLink({ href }: Link): boolean {
-  return /^https?:\/\//.test(href) && !getUrlMimeType(href);
+  return /^https?:\/\//.test(href) && !getUrlMediaType(href);
 }
 
 /** Ensures the Link is a URL so it can be parsed. */
@@ -87,17 +85,6 @@ function isLinkURL(link: Link): boolean {
   return link.type === 'url';
 }
 
-/** Get the extension from the URL, then get its type. */
-function getUrlMimeType(url: string): string | undefined {
-  try {
-    const { pathname } = new URL(url);
-    const ext = pathname.split('.').pop() ?? '';
-    return typeByExtension(ext);
-  } catch {
-    return undefined;
-  }
-}
-
 /** Get pubkey from decoded bech32 entity, or undefined if not applicable. */
 function getDecodedPubkey(decoded: nip19.DecodeResult): string | undefined {
   switch (decoded.type) {
diff --git a/src/utils/media.test.ts b/src/utils/media.test.ts
new file mode 100644
index 00000000..e88e97da
--- /dev/null
+++ b/src/utils/media.test.ts
@@ -0,0 +1,17 @@
+import { assertEquals } from '@std/assert';
+
+import { getUrlMediaType, isPermittedMediaType } from '@/utils/media.ts';
+
+Deno.test('getUrlMediaType', () => {
+  assertEquals(getUrlMediaType('https://example.com/image.png'), 'image/png');
+  assertEquals(getUrlMediaType('https://example.com/index.html'), 'text/html');
+  assertEquals(getUrlMediaType('https://example.com/yolo'), undefined);
+  assertEquals(getUrlMediaType('https://example.com/'), undefined);
+});
+
+Deno.test('isPermittedMediaType', () => {
+  assertEquals(isPermittedMediaType('image/png', ['image', 'video']), true);
+  assertEquals(isPermittedMediaType('video/webm', ['image', 'video']), true);
+  assertEquals(isPermittedMediaType('audio/ogg', ['image', 'video']), false);
+  assertEquals(isPermittedMediaType('application/json', ['image', 'video']), false);
+});
diff --git a/src/utils/media.ts b/src/utils/media.ts
new file mode 100644
index 00000000..9c0ea9e3
--- /dev/null
+++ b/src/utils/media.ts
@@ -0,0 +1,24 @@
+import { typeByExtension } from '@std/media-types';
+
+/** Get media type of the filename in the URL by its extension, if any. */
+export function getUrlMediaType(url: string): string | undefined {
+  try {
+    const { pathname } = new URL(url);
+    const ext = pathname.split('.').pop() ?? '';
+    return typeByExtension(ext);
+  } catch {
+    return undefined;
+  }
+}
+
+/**
+ * Check if the base type matches any of the permitted types.
+ *
+ * ```ts
+ * isPermittedMediaType('image/png', ['image', 'video']); // true
+ * ```
+ */
+export function isPermittedMediaType(mediaType: string, permitted: string[]): boolean {
+  const [baseType, _subType] = mediaType.split('/');
+  return permitted.includes(baseType);
+}