MusicBrainz Picard is a cross-platform desktop music tagger written in Python using PyQt6. It is the official tagger for the MusicBrainz music metadata database. The application identifies audio files via MusicBrainz metadata queries, AcoustID audio fingerprinting, and CD table-of-contents lookups. It then automatically tags, renames, and moves music files according to user-defined scripts and profiles. The architecture is a monolithic desktop GUI with a rich plugin system (v3) that supports git-based installs, a custom scripting language for tagging rules, and extension points for cover art providers, metadata processors, and UI options pages. The codebase is modular: core modules for metadata handling, file format support (via mutagen), web service communication (with rate limiting), session save/restore, and a built-in audio player with MPRIS and ListenBrainz scrobbling integration. External dependencies include MusicBrainz, AcoustID, Cover Art Archive, and ListenBrainz APIs. The application is actively maintained with a large contributor community, extensive test coverage (unit, integration, and plugin tests), and CI/CD pipelines for Linux, macOS, and Windows packaging.