CosmoNote is a web-based application for visualizing and annotating expressive structures in performed music. This demo highlights the flexibility of CosmoNote's reconfigurable interface, features, and toolsets to design experiments to advance knowledge in music science, music perception, and music expressivity. CosmoNote's music pieces are organized into collections accessible by user accounts with defined roles. The music representations integrate synchronized visual layers representing recorded piano performance data and features to facilitate and inform annotations. The web app provides four annotation types: boundaries, regions, note-groups and comments. Through the selection of pieces, collections and user roles, Cos-moNote's features can be tailored to investigate diverse research questions about experimental design for music audio-based annotations.