Developer platform · 0.1 alpha

Casset Apps

Build apps for artist worlds.

Create a focused interface inside a living Profile World or let a visual experience move with one host-authorized Track. The SDK, fixtures, and starters are real today; production distribution is still curated and internal.

Start the quickstart Download React starter

@casset/apps is repository-local and vendored into each ZIP. It is not published to npm, and there is no public submit flow.

One playback authorityThe song stays in Casset.repository local

Apps receive

Bounded artist, theme, catalog, and release data
Explicit loading, empty, denied, and unavailable states
Synchronized Track seconds and lifecycle
Narrow host capability checks

Casset retains

Installation, entitlement, and launch authority
The global player and canonical audio clock
Routes, runtime dispatch, and raw media delivery
Disablement, exit, and production integration

manifesthost contextyour interface

Available now

Two runtimes, one product model.

Casset Apps deepen artist identity and the listening ritual. They do not become microsites, replacement players, or generic dashboards.

Profile World appsStage approved identity, atmosphere, catalog, liner notes, and one active release inside an artist-owned surface.available · Profile Surface Track experiencesProject a deterministic visual frame from Casset's synchronized Track context without owning audio or inventing a clock.available · read only Catalog utilitiesBuild a bounded listening index or release artifact from the Profile catalog projection and approved host requests.available · bounded data Campaign and audience viewsThe permission vocabulary exists, but generic public data adapters do not. These families remain explicitly unavailable.unavailable · future adapter

Five-minute start

Download, verify, then make it yours.

Each immutable ZIP contains the starter, the exact SDK alpha as a local file dependency, deterministic fixtures, tests, and agent instructions. No Casset credential is required.

Unpack

Choose a Profile or Track starter and enter its root folder.

Verify

Install dependencies, run tests, and build before changing the contract.

Compose

Change the manifest and interface; keep host authority and state handling intact.

curl -LO https://casset.fm/downloads/casset-apps/casset-minimal-profile-app-v0.1.0-alpha.0.zip
unzip casset-minimal-profile-app-v0.1.0-alpha.0.zip
cd casset-minimal-profile-app
pnpm install
pnpm test
pnpm dev

Open the full quickstart Compare all starters Open the agent brief Inspect download checksums

SDK and imports

A real package, a declaration, and a narrow host.

The repository-local @casset/apps alpha turns the trusted runtime into a small developer contract. It is vendored into every ZIP as a local file dependency; Casset's server and host remain the only launch authority.

@casset/appsvendored host contract

typescriptcontract checking

vitelocal build

vitestfixture and state tests

reactReact starter only

Manifest

Identity and version
Profile or Track context
Placements and permissions
Track kinds when applicable

Context

Short-lived launch lifecycle
Minimized public DTOs
Explicit Profile data states
URL-free Track resource references

Host

Capability detection
Profile-only PLAY_TRACK request
Lifecycle subscriptions
Fail-closed close and invalid requests

import {
  hasCassetPermission,
  hostSupports,
  isCassetDataReady,
  type CassetAppHost,
} from "@casset/apps"

export async function playFirstTrack(host: CassetAppHost) {
  const { context } = host.getSnapshot()
  if (context.kind !== "PROFILE_SURFACE") return
  if (!isCassetDataReady(context.catalog)) return
  if (!hasCassetPermission(context, "playback.control")) return
  if (!hostSupports(host, "PROFILE_PLAY_TRACK")) return

  const track = context.catalog.data.tracks[0]
  if (track) await host.request({ type: "PLAY_TRACK", trackId: track.id })
}

{
  "schema": "casset.app-manifest.v1",
  "id": "studio.afterglow-room",
  "slug": "afterglow-room",
  "name": "Afterglow Room",
  "shortDescription": "A quiet release room inside the Profile World.",
  "description": "Stages an approved release and requests playback through Casset.",
  "developer": { "name": "Your studio" },
  "version": "0.1.0",
  "icon": "/icon.svg",
  "screenshots": [],
  "category": "IDENTITY",
  "context": "PROFILE_SURFACE",
  "placements": ["ARTIST_APP_ROUTE"],
  "permissions": [
    "artist.profile.read",
    "artist.theme.read",
    "catalog.tracks.read",
    "playback.read",
    "playback.control"
  ],
  "supportedFanAccess": ["FREE"],
  "compatibility": { "mobile": true, "desktop": true, "pwa": true },
  "trackApplicability": null
}

@casset/apps is not published to npm. The starter ZIPs include the exact pre-release source and install it through a local file: dependency, so the imports above are real without implying an open package or marketplace.

Agent-ready Markdown

Give Codex or Claude a bounded creative brief.

Every starter includes AGENTS.md, CLAUDE.md, PROMPT.md, and a README. The system instructions hold the runtime boundary; the prompt below is where you describe the emotional interface you want to make.

AGENTS.md

Canonical Casset doctrine
Files the agent may change
Runtime authority rules
Required validation commands

CLAUDE.md

The same host boundary
Sparse-state expectations
Mobile and reduced-motion rules
No second player or private data

PROMPT.md

A reusable task brief
Creative intent and interaction
Acceptance criteria
Test and build handoff

# Build brief for Codex or Claude Code

## Objective
Turn the artist's active release into a quiet afterglow room inside
the existing Profile World.

## Use
- The vendored `@casset/apps` package
- The provided fixture and host lifecycle
- The starter's existing test and build commands

## Preserve
- Casset owns artist identity, authorization, playback, and exit
- Request playback through the host; never mount an `<audio>` element
- Handle loading, empty, unavailable, and permission-denied states
- Keep the interface calm, mobile-first, and artist-specific

## Verify
- `pnpm test`
- `pnpm build`

Runnable projects

Begin at the right level of abstraction.

All three starters consume the same package. Their visual language is intentionally restrained; the bundled prompts tell Codex and Claude Code to create an original App rather than clone the sample.

Minimal Profile AppDependency-light TypeScript and DOM. Exercises ready, loading, empty, unavailable, and permission-denied catalog states.ZIP · minimal React Profile AppTyped React surface with lifecycle updates, release data, responsive composition, and host-approved Track requests.ZIP · intermediate Track ExperienceRead-only canonical playback projection, deterministic visual phases, lifecycle cleanup, and one local interaction.ZIP · advanced Starter guideChoose a kit, copy an agent prompt, inspect every included file, and follow the supported local workflow.Docs · agent ready

Truth before scale

A real SDK is not an open marketplace.

The package and downloads are usable. Third-party accounts, arbitrary production bundle execution, credentials, submission, signing, resource brokering, and public installation have not shipped.

Use now

Repository-local @casset/apps
Three standalone starter ZIPs
Strict parsers and fixtures
Trusted production Track contract

Casset only

Registry and runtime keys
Installation and entitlement truth
Playback stores and MediaFooter
Raw media and server authorization

Not shipped

npm publication
Public submit or review API
Arbitrary bundle isolation
Live revocation and resource delivery

Current distributionBuild against the truth that exists today.Read distribution status

Build apps for artist worlds.

@casset/apps is repository-local and vendored into each ZIP. It is not published to npm, and there is no public submit flow.

curl -LO https://casset.fm/downloads/casset-apps/casset-minimal-profile-app-v0.1.0-alpha.0.zip unzip casset-minimal-profile-app-v0.1.0-alpha.0.zip cd casset-minimal-profile-app pnpm install pnpm test pnpm dev

import { hasCassetPermission, hostSupports, isCassetDataReady, type CassetAppHost, } from "@casset/apps" export async function playFirstTrack(host: CassetAppHost) { const { context } = host.getSnapshot() if (context.kind !== "PROFILE_SURFACE") return if (!isCassetDataReady(context.catalog)) return if (!hasCassetPermission(context, "playback.control")) return if (!hostSupports(host, "PROFILE_PLAY_TRACK")) return const track = context.catalog.data.tracks[0] if (track) await host.request({ type: "PLAY_TRACK", trackId: track.id }) }

{ "schema": "casset.app-manifest.v1", "id": "studio.afterglow-room", "slug": "afterglow-room", "name": "Afterglow Room", "shortDescription": "A quiet release room inside the Profile World.", "description": "Stages an approved release and requests playback through Casset.", "developer": { "name": "Your studio" }, "version": "0.1.0", "icon": "/icon.svg", "screenshots": [], "category": "IDENTITY", "context": "PROFILE_SURFACE", "placements": ["ARTIST_APP_ROUTE"], "permissions": [ "artist.profile.read", "artist.theme.read", "catalog.tracks.read", "playback.read", "playback.control" ], "supportedFanAccess": ["FREE"], "compatibility": { "mobile": true, "desktop": true, "pwa": true }, "trackApplicability": null }

# Build brief for Codex or Claude Code ## Objective Turn the artist's active release into a quiet afterglow room inside the existing Profile World. ## Use - The vendored `@casset/apps` package - The provided fixture and host lifecycle - The starter's existing test and build commands ## Preserve - Casset owns artist identity, authorization, playback, and exit - Request playback through the host; never mount an `<audio>` element - Handle loading, empty, unavailable, and permission-denied states - Keep the interface calm, mobile-first, and artist-specific ## Verify - `pnpm test` - `pnpm build`