One or more albums. Each starts with an "Artist - Title" line, then Release Date, Duration, then the numbered tracklist. Two-disc albums: put "Disc 1:" / "Disc 2:" lines before each disc's tracks. Duplicates (same artist + title) are skipped.
Your crate and listened marks live in this browser. Export a backup before switching devices or clearing browser data, then import it on the other side.
Reset the whole app back to the original list (this clears your added albums and listened marks):