ExplicitTagger

A lightweight macOS utility for setting iTunes content advisory tags on AAC and Apple Lossless audio files. Drag in a file, pick a mode, done.

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What it does

ExplicitTagger writes directly to the rtng atom inside the MP4 container of .m4a and .alac files — the same metadata field iTunes and Apple Music read to display the E or CLEAN badge on a track. No iTunes required, no third-party libraries, just pure Swift byte manipulation.

Three modes:

Button	Tag value	Result in iTunes / Apple Music
Explicit	1	Shows E badge
Clean	2	Shows CLEAN badge
Remove Tag	0	Removes advisory entirely

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Features

• Drag and drop .m4a or .alac files onto the window, or click to open via file picker
• Creates the rtng atom from scratch if one doesn't already exist
• Patches atom tree sizes all the way up (ilst → meta → udta → moov) for spec-compliant output
• Writes are atomic (temp file + rename) — original is never left in a partial state
• Universal binary — runs natively on Apple Silicon and Intel
• Retro Aqua-inspired UI, no Electron, no Python, no dependencies

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Requirements

• macOS 13 Ventura or later
• Xcode command line tools (for building)

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Building

git clone https://github.com/your-username/ExplicitTagger.git
cd ExplicitTagger/AdvisoryTagger
bash build_app.sh

This produces ExplicitTagger.app in the AdvisoryTagger folder. Drag it to /Applications or run it from wherever you like.

First launch: because the app is ad-hoc signed rather than notarized, Gatekeeper will block it on the first open. Right-click → Open → Open to allow it once. After that it launches normally.

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Project structure

AdvisoryTagger/
├── Package.swift
├── build_app.sh
└── Sources/ExplicitTagger/
    ├── ExplicitTaggerApp.swift   # App entry point, AppDelegate, font registration
    ├── ContentView.swift         # Main UI (SwiftUI)
    ├── AboutView.swift           # About window
    ├── MP4Tagger.swift           # Pure Swift MP4 atom reader/writer
    └── Resources/
        ├── icon.png
        └── AppleGaramond-Light.ttf

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Disclaimer

ExplicitTagger is an independent utility and has no affiliation with Apple Inc. iTunes and Apple Music are trademarks of Apple Inc.