There is no reason Apollo shouldn't work on mobile, but right now it isn't really usable on a mobile device, which is something that should be remedied. Since certain parts look broken and others look sub-optimal, this is being marked as both a bug and an enhancement.

At the moment, all album art and data is provided by Spotify, and is therefore usable in the service without problems...as long as the API is used according to guidelines and branding constraints. However, there are a few album covers found on the introduction page, which shows up before someone logs in via Spotify. I'm not certain if this violates usage restrictions of album art and material that belongs to a record label / music entity. Since I'm not sure if you have reviewed this yet or not, or have received permissions for such displays, I am creating this issue now but understand if it gets closed rapidly.

Playlists and Albums are made up of tracks, and users should be able to view these tracks to then jump to song analysis or song comparison.

Albums, tracks, and artists all have a popularity that is computed by Spotify. This metric should when retrieving those objects in Apollo. It should also be aggregated when doing analysis of multiple objects to provide metrics like the average popularity of songs in a playlist or an album.

By requesting a few more permissions, Apollo can access a users' saved tracks, saved albums, and playlists, and could allow for easy navigation to analyse these objects. Check out the Spotify API User Library for the API requests needed for that.

When looking at an individual song, an Apollo user should be able to press a button to load that song into song comparison, so that they only have to pick a second song to compare with. Likewise the individual song page should link to album comparison for the album that the song is on.

Spotify requires linking back to their service per [their TOS] Section IV 3 g:

Metadata, Cover Art, and Audio Clip-Specific Restrictions. Metadata, cover art and Audio Preview Clips available via the Spotify Platform shall include a link back to the applicable artist, album, track, or playlist on the Spotify Service. You shall use the identifiers provided by Spotify via the Spotify Platform in order to comply with the restrictions in this paragraph. You shall clearly attribute that the Audio Preview Clips are being supplied and streamed by Spotify using the designated Spotify Marks on the player. You shall not offer metadata, cover art, and/or Audio Preview Clips as a standalone service or product.

This means Apollo should link back to artists or tracks on Spotify and make sure it's very clear that the preview tracks are coming from Spotify

Apollo uses font-weight: 600 on all <h1> tags, but only loads weight 400 and 700 of Montserrat. Loading in font-weight 600 fixes this issue.

Spotify has an API endpoint for fetching artist data (see here), and this should be used to add some specific artist based features (in addition to basic information display). These could include links to analyze the artists albums or top tracks, or an aggregate graph of the features of their top tracks.

Looking at an album is fairly empty:

Adding in a list of the songs on the album would fill out the space and serve as a useful tool.

Spotify login to Apollo should persist using a cookie, as a user should not have to sign in every time they visit the site or even just refresh Apollo.

Query parameters can be used to share a specific view in Apollo. This means query params need to be able to specify the current view (single song, song comparison, album, or playlist as of the creation of this issue) as well as the ID of the object(s) being viewed.

Since you still need to authorize Apollo when going to a shared link, show an authorize popup over the blurred actual post auth screen rather than showing the intro screen