diff --git a/apps/mukke/CLAUDE.md b/apps/mukke/CLAUDE.md
index 003975f88..f7da41e42 100644
--- a/apps/mukke/CLAUDE.md
+++ b/apps/mukke/CLAUDE.md
@@ -120,6 +120,28 @@ pnpm --filter @mukke/landing dev      # Landing page
 { id, lyricsId, lineNumber, text, startTime, endTime }
 ```
 
+## Supported Audio Formats
+
+Playback uses HTML5 Audio (browser-native codec support). Upload accepts any `audio/*` MIME type.
+
+| Format | Extensions | Browser Playback | Notes |
+|--------|-----------|-----------------|-------|
+| MP3 | `.mp3` | All browsers | ID3 tag read/write supported |
+| WAV | `.wav` | All browsers | Uncompressed PCM |
+| OGG Vorbis | `.ogg` | Chrome, Firefox, Edge | No Safari support |
+| FLAC | `.flac` | All modern browsers | Lossless |
+| AAC/M4A | `.aac`, `.m4a` | All browsers | Common iOS format |
+| OPUS | `.opus` | Chrome, Firefox, Edge | Best quality/size ratio |
+| WebM | `.webm` | Chrome, Firefox, Edge | Container format |
+| AIFF | `.aiff`, `.aif` | Safari, Chrome | Common macOS format |
+| WMA | `.wma` | Edge only | Legacy Windows format |
+| ALAC | `.alac` | Safari | Apple Lossless |
+| APE | `.ape` | None natively | Monkey's Audio (upload/metadata only) |
+| WavPack | `.wv` | None natively | Hybrid lossless (upload/metadata only) |
+| DSF/DFF | `.dsf`, `.dff` | None natively | DSD audio (upload/metadata only) |
+
+**Note:** Formats without native browser playback can be uploaded and have metadata extracted (via `music-metadata`), but require server-side transcoding for playback (not yet implemented).
+
 ## Key Technologies
 
 | Component | Technology |
diff --git a/packages/shared-storage/src/utils.test.ts b/packages/shared-storage/src/utils.test.ts
new file mode 100644
index 000000000..a71307cd2
--- /dev/null
+++ b/packages/shared-storage/src/utils.test.ts
@@ -0,0 +1,73 @@
+import { describe, it, expect } from 'vitest';
+import { getContentType, validateFileExtension, AUDIO_EXTENSIONS } from './utils';
+
+describe('getContentType', () => {
+	describe('audio formats', () => {
+		const audioMappings: [string, string][] = [
+			['.mp3', 'audio/mpeg'],
+			['.wav', 'audio/wav'],
+			['.ogg', 'audio/ogg'],
+			['.m4a', 'audio/mp4'],
+			['.aac', 'audio/aac'],
+			['.flac', 'audio/flac'],
+			['.aiff', 'audio/aiff'],
+			['.aif', 'audio/aiff'],
+			['.opus', 'audio/opus'],
+			['.wma', 'audio/x-ms-wma'],
+			['.alac', 'audio/mp4'],
+			['.ape', 'audio/x-ape'],
+			['.wv', 'audio/x-wavpack'],
+			['.dsf', 'audio/dsf'],
+			['.dff', 'audio/dff'],
+		];
+
+		it.each(audioMappings)('%s → %s', (ext, expected) => {
+			expect(getContentType(`song${ext}`)).toBe(expected);
+		});
+
+		it('handles uppercase extensions', () => {
+			expect(getContentType('song.FLAC')).toBe('audio/flac');
+			expect(getContentType('song.M4A')).toBe('audio/mp4');
+		});
+
+		it('returns application/octet-stream for unknown extensions', () => {
+			expect(getContentType('song.xyz')).toBe('application/octet-stream');
+		});
+	});
+});
+
+describe('AUDIO_EXTENSIONS', () => {
+	it('contains all common audio formats', () => {
+		const expected = [
+			'.mp3',
+			'.wav',
+			'.ogg',
+			'.m4a',
+			'.aac',
+			'.flac',
+			'.aiff',
+			'.aif',
+			'.opus',
+			'.wma',
+			'.webm',
+			'.alac',
+			'.ape',
+			'.wv',
+			'.dsf',
+			'.dff',
+		];
+		for (const ext of expected) {
+			expect(AUDIO_EXTENSIONS).toContain(ext);
+		}
+	});
+});
+
+describe('validateFileExtension', () => {
+	it('validates audio files against AUDIO_EXTENSIONS', () => {
+		expect(validateFileExtension('song.flac', AUDIO_EXTENSIONS)).toBe(true);
+		expect(validateFileExtension('song.mp3', AUDIO_EXTENSIONS)).toBe(true);
+		expect(validateFileExtension('song.opus', AUDIO_EXTENSIONS)).toBe(true);
+		expect(validateFileExtension('song.exe', AUDIO_EXTENSIONS)).toBe(false);
+		expect(validateFileExtension('song.pdf', AUDIO_EXTENSIONS)).toBe(false);
+	});
+});