A case study of Harmony — a web app that lets friends share playlists across Spotify, Apple Music, and YouTube Music.
Music is social. Streaming platforms aren't.
As of 2025, 921.6 million people worldwide are subscribed to a music streaming service. Of these subscribers, 31% belong to Spotify, 13% to Apple Music, and 12% to YouTube Music — with the remaining share fractured across even more platforms.1 Evidently, the global music streaming population is split into platforms that do not communicate with one another.
This digital division can split friends, family, and even romantic partners. A poll of 95 college-aged adults found that 74% had friends or family that used a competing music streaming service.
Interviews with specific individuals uncovered the following:
Services already exist that allow users to transfer playlists from one streaming service to another, though they mainly act as account migration tools. Those that allow playlist sharing can turn a playlist into a link that opens on whatever service the recipient uses — proof that the technology backing Harmony is realistic and commercially viable.
What none of them build is a relationship. Their sharing is a link you generate and paste somewhere — anonymous, one-directional, and finished the moment it's opened. There is no friends list, no inbox of playlists from specific people, no record of who you actually trade music with. Sharing is a byproduct of a transfer tool rather than the point of the product.
Hence Harmony's thesis: be the social layer between services, not another migration tool. Keep everyone on the platform they already love; make the playlist the thing that travels.
| Alternative | What it does | The gap Harmony targets |
|---|---|---|
| TuneMyMusic | Transfers libraries between services, and turns a playlist into a shareable page whose visitors can import it to their own library. Sharing is on the free tier; transfers cap at 500 tracks.2 | The closest thing to Harmony's loop — but it ends at the link. No friends, no inbox, no sender attached to what you receive. |
| Soundiiz | Rebuilds collections across 40+ services; free Smartlinks route listeners to a playlist on the platform of their choice. Free transfers cap at 200 tracks per playlist.3 | Smartlinks are a curator-and-artist promotion tool aimed at an audience, not a person, and they point at the live playlist rather than the version you meant to send. |
| SongShift | iPhone and iPad app that transfers and shares playlists across 13+ services; free to use, with a Pro tier for batch and sync features.4 | iOS only — it can't reach the Android half of the split it exists to solve. |
Competitive landscape verified August 2026. All three now offer some form of cross-platform sharing — the unclaimed ground is sharing built around a standing friendship rather than a link.
Sign in with your streaming service, share playlists with friends on any other.
These demos are live. Each frame renders the same React components as the live web-app. Server calls are swapped for local simulations running on sample data. Because the exhibits import the production components, they update automatically as Harmony evolves.
The home screen puts all of a user's libraries side by side — Spotify, Apple Music, YouTube Music — each in its own branded card with the attribution and link-backs the services require. Search spans all of them at once, because nobody remembers which platform a playlist lives on. Most people use just one, so the demo account starts on Spotify alone; connecting another is the power-user path.
Sharing is the heart of the product. Every row can be sent to friends or turned into a public link, and incoming shares arrive in an inbox where one tap converts the playlist into your own library — with live per-track progress and an honest match report at the end, including which tracks matched loosely and which couldn't be found.
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HYPE UP
Nicholas · 42 tracks
lets goooooooo
gym (new)
Nicholas · 67 tracks
Focus
Nicholas · 38 tracks
sleep
Nicholas · 25 tracks
the other half of the bio
concert prep
Nicholas · 56 tracks
3am
Nicholas · 19 tracks
don't ask
Apple and Apple Music are trademarks of Apple Inc., registered in the U.S. and other countries. Spotify is a trademark of Spotify AB. YouTube and YouTube Music are trademarks of Google LLC. Harmony is not endorsed by or affiliated with any of these services.
Harmony deliberately has no follower counts and no feed. Friendship is mutual, profiles are visible to friends only, and the list is sorted like an inbox — the people you most recently exchanged music with float to the top, with the running count of playlists exchanged as the row's only metric. The number that matters is between the two of you.
Tapping a row opens that friend's profile: bio, mutual friends, the friendship's stats, and their favorite playlists — up to four pinned picks any friend can save straight into their own library, with the save count flowing back to the owner.
Growth runs through the same screen: search by username for people already on Harmony, or send an invite link to someone who isn't — the link lands them in onboarding and completes the friendship once they've signed in.
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Sign-in is service-linking: authenticating with Spotify, Google, or Apple both creates the Harmony identity and connects that service, so there's no separate “connect your accounts” chore. The account screen shows each service's state and lets users link the rest of the lineup — every row identical, one state and one action apiece.
The screen is also where identity gets its color: a Favorite Playlists grid — four slots, Letterboxd's four favorites, for music — that friends see on your profile. Picks come from every linked service through one picker, tiles reorder with two taps instead of a drag library, and each favorite stores a snapshot friends can save into their own libraries.
Apple Music is the exception that proves the rule. Its library permission is a second, browser-local connection that Sign in with Apple doesn't cover, and an earlier build surfaced it right here — a row that could read “Account connected” while the library wasn't, asymmetric against its neighbours and asking for a permission nothing on screen used. It now lives on the playlists screen, prompted at the moment the library is actually read.
Destructive actions get friction proportional to their consequence: removing a friend is a confirm dialog, deleting an account is a quiet text link that demands you type your username. Profile edits stage locally — photo upload with pan/zoom crop, or adopting a photo from a linked service — and commit in one save.
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Spotify
Linked July 4, 2026
Apple Music
Not connected
YouTube Music
Not connected
Apple and Apple Music are trademarks of Apple Inc., registered in the U.S. and other countries. Spotify is a trademark of Spotify AB. YouTube and YouTube Music are trademarks of Google LLC. Harmony is not endorsed by or affiliated with any of these services.
Every share has a public face. A playlist can be handed to anyone as a link — the page renders its snapshot, with the required per-service attribution, for visitors with no Harmony account at all. And every user has an invite link built to be texted to someone who's never heard of the app, with metadata that gives iMessage and social previews the sender's name and picture.
These pages are where the growth loop lives or dies, so their most fragile step is made boring: signing in from either one carries a validated ?next= path through the whole OAuth round-trip, landing the visitor back on the exact link they clicked with its actions now unlocked. The demo simulates that round-trip — sign in with any service and the page picks up right where you left it.
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Morning Song
Birdhouse · Songbird
Trees Through the Blinds
The Night Shift · Window Seat
Cold Feet
Paper Skeleton · Freezer Burn
Porch Light
Low Orbit Club · House in Orbit
Sing Anyway
Birdhouse · Songbird
Sun Hat
Solar Kite · Too Close to the Sun
Stargazing From the Couch
Low Orbit Club · House in Orbit
Long Nap
The Night Shift · Window Seat
Freezer Aisle Funk
Paper Skeleton · Freezer Burn
Wax Wings
Solar Kite · Too Close to the Sun
Apple and Apple Music are trademarks of Apple Inc. Spotify is a trademark of Spotify AB. YouTube and YouTube Music are trademarks of Google LLC. Harmony is not endorsed by or affiliated with any of these services.
Exactly what a link recipient sees — no account needed to look.
The decisions that drove Harmony's development.
Where it stands, and what building it taught me.
Harmony works end to end today: sign in with any of the three services, link the others, and share playlists with friends — or with anyone, via public snapshot links — while every profile carries its owner's pinned favorites for friends to save from directly. The primary constraint on growth is external: Spotify and Google keep new applications in development mode with capped user allowlists, so onboarding remains invite-based while the app pursues production API access.
What I learned: more than anything, Harmony reinforced that form follows function. The strongest interfaces weren't the ones that started as visual explorations — they were the ones that grew naturally from carefully defining what the product needed to accomplish. Every decision became an exercise in communicating the maximum amount of information with the minimum amount of visual noise. I also learned that technical constraints aren't always limitations; API capabilities, branding requirements, and platform conventions often become the framework that gives a product its character. Designing within those boundaries consistently led to cleaner, more intuitive solutions than trying to fight them.
What's next: production API access, album reviews, richer sharing with notes, and more.
