A real AI-assisted build

How Mainstreetfy became a responsive, working app.

A beginner-friendly look at the decisions, mistakes, cleanup, testing, and deployment behind a music experience built with AI.

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Mainstreetfy desktop app with music navigation, recommendations, and a persistent player — The deployed desktop experience.

What we built

One product, two deliberate experiences.

Mainstreetfy is a responsive music app inspired by the familiar rhythm of modern streaming products. Desktop gets a roomy navigation and discovery layout. Mobile gets a focused feed and a full-screen player. Both use the same underlying player state.

React + TypeScriptA component-based interface built for safe iteration.

Responsive by designDesktop and phone layouts serve the same product differently.

No backend requiredLocal data keeps this first version lightweight.

Original visual assetsArtwork is generated with CSS rather than copied album covers.

Mobile is not a squeezed desktop

The phone experience got its own priorities.

On a smaller screen, the app keeps discovery scannable and the player easy to reach. Opening a track moves into a dedicated player instead of trying to preserve every desktop panel.

Compact home feed with large touch targets
Persistent mini-player for the current track
Dedicated full-screen player on mobile
Shared playback, progress, and volume behavior

Mainstreetfy mobile home screen with playlists and a mini-player — Mobile discovery

Mainstreetfy full-screen mobile music player — Full-screen player

The real implementation story

The useful work continued after the first screen looked finished.

Build the complete interface

The first pass established the discovery pages, navigation, responsive layouts, player controls, and original artwork. That made the full experience visible early enough to test.

Remove infrastructure the product did not need

The initial project also carried generic authentication, database, and backend starter files. None supported this version’s outcome, so they were removed instead of becoming accidental complexity.

Replace starter checks with product checks

Some tests still described the old starter screen. They were rewritten to confirm that the finished app renders and that its desktop, mobile, and missing-audio safeguards remain present.

Deploy the honest version

The app was published with the approved track and a safe fallback for missing audio. The player explains what is available without hiding unfinished dependencies.

Architecture, without the jargon

Keep one source of truth for behavior.

The most important structural decision was not a visual one. Track selection, play and pause, progress, volume, shuffle, and repeat belong to one shared player state. Desktop and mobile are different views of that same state.

Shared player state

Desktop experienceMobile experience

Local track + app data

Lessons you can reuse

Five ideas matter more than the music-app theme.

Start with a visible outcome

A complete user journey gives you something real to evaluate earlier than a long infrastructure phase.

Delete borrowed complexity

A starter project is a toolbox, not a requirement list. Remove systems that do not support the current outcome.

Test what the product became

Passing tests are only helpful when their expectations still match the experience users receive.

Design mobile intentionally

Responsive work is about priorities and interaction, not only making boxes narrower.

Be honest about missing inputs

A safe fallback is better than bundling an unapproved asset or disguising an unfinished dependency.

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The Mainstreetfy Build Kit

Unlock the demo, source code, and complete build brief.

The case study stays public. Enter your email once to open the working app, explore the GitHub repository, and reveal the reusable brief behind the build.

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Open the working app, inspect the source, and copy the complete brief below.

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Reusable Codex brief

Build a responsive media app with one shared player

You are working in an existing web project. Build a polished, responsive media app called [APP NAME].

GOAL
Create one complete discovery-to-playback experience that works on desktop and phone. The first version should feel finished without requiring accounts, payments, a database, or a backend.

USERS AND OUTCOME
- Primary user: [DESCRIBE THE USER].
- Main outcome: browse recommended media, choose an item, and control playback.
- Success evidence: the interface renders at desktop and phone widths, the same selected item appears everywhere, and controls update one shared player state.

DESKTOP EXPERIENCE
- Provide clear left navigation, a central discovery area, and useful secondary context.
- Keep a persistent player visible at the bottom.
- Show realistic sample collections, recommendations, and track metadata.

MOBILE EXPERIENCE
- Treat mobile as a deliberate layout, not a squeezed desktop.
- Prioritize a scannable home feed, reachable navigation, and large touch targets.
- Keep a compact mini-player visible.
- Open a dedicated full-screen player for the selected item.

SHARED PLAYER BEHAVIOR
- Use one source of truth for selected track, play/pause, progress, volume, shuffle, and repeat.
- Keep desktop and mobile controls synchronized.
- If the audio file is absent or cannot play, fail safely and tell the user what is missing.

CONTENT AND VISUALS
- Use original placeholder artwork or CSS-generated visuals. Do not copy copyrighted album covers.
- Keep sample data in a small local module so it can be replaced later.
- Preserve a coherent visual identity across screen sizes.

NON-GOALS FOR V1
- No authentication, user profiles, payments, database, admin panel, uploads, or recommendation engine.
- Do not add infrastructure unless the visible outcome actually requires it.

QUALITY REQUIREMENTS
- Use semantic controls, useful alt text, visible keyboard focus, and labels for icon-only buttons.
- Prevent horizontal overflow and verify small-phone and wide-desktop layouts.
- Add automated checks for the finished product, not starter content.
- Confirm that the production build succeeds and document any missing asset honestly.

WORKFLOW
1. Inspect the existing project and summarize the smallest implementation plan.
2. Build the full visible journey with realistic local data.
3. Test desktop and mobile behavior.
4. Remove unused starter infrastructure and update stale tests.
5. Run the production build and relevant checks.
6. Report what changed, what is intentionally excluded, and what input is still needed.

Do not claim success from code alone. Verify the rendered experience and preserve unrelated working behavior.

Make it yours in four edits

Rename the product and identify its user.
Replace the music data with your own media type.
Choose the one journey users must complete.
Keep everything else in “not in V1” until evidence requires it.

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