metaedit

0006. Map Last.fm styles onto BaseItemDto.Tags; genres onto Genres

• Status: Accepted
• Date: 2026-10-06

Context

The Last.fm API exposes one flat set of community tags per artist, album and track, each with a popularity count. It has no genre/style distinction. Jellyfin items have both a Genres array and a Tags array; only Genres gets genre-entity treatment and navigation.

Decision

Treat “genre” and “style” as our mapping concepts over the single Last.fm tag set:

• The highest-ranked LASTFM_GENRE_LIMIT tags become Genres.
• The next LASTFM_STYLE_LIMIT tags become Tags (the style bucket).
• Both are merged with existing values rather than replacing them, by default.

The split points, the minimum tag count, the blacklist and the caps are all configuration, never hard-coded.

Consequences

• The mapping is honest about what Last.fm provides and fully tunable without re-fetching anything, because the raw archive is retained (ADR 0008/0009).
• Retuning the split is a reindex, not a re-crawl.
• Genre entity creation in Jellyfin is a server concern; whether a new genre appears immediately or on the next library scan is recorded in the README as observed behaviour rather than assumed.

Alternatives rejected

• Everything into Genres. Rejected: it floods genre navigation with descriptive noise such as seen live or british.
• Everything into Tags. Rejected: Jellyfin clients then show no genres at all for music, which is the primary thing users filter by.
• Guessing genres from a bundled genre list. Rejected: an opinionated classifier with its own maintenance burden, for a problem the operator can solve by tuning two integers.