App Index Schema

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App Index Schema

The App Index is a JSON document format for describing application metadata across platforms and distribution channels. It provides a structured, machine-readable catalog of an application’s localized descriptions, permissions, icons, screenshots, distribution links, and source repository information.

Schema URI: https://appfair.org/schemas/appindex/v1.json

Specification version: 1.0

Overview

An App Index document is a single JSON file (conventionally named appindex.json) that contains all user-facing metadata for one or more applications. The format is platform-agnostic: the same schema supports mobile, desktop, and web applications across any operating system and distribution channel.

{
  "$schema": "https://appfair.org/schemas/appindex/v1.json",
  "specVersion": "1.0",
  "generated": "2026-05-01T18:00:00Z",
  "generator": "skip/1.8.11",
  "apps": [
    {
      "name": "MyApp",
      "title": { "en": "My App" },
      "description": { "en": "A great app." },
      "keywords": { "en": ["app", "great"] },
      "links": { ... },
      "source": { ... },
      "platforms": {
        "ios": { "version": "1.0.0", ... },
        "android": { "version": "1.0.0", ... }
      }
    }
  ]
}

Document Structure

Top-Level Fields

Field	Type	Required	Description
`$schema`	string	yes	Must be `"https://appfair.org/schemas/appindex/v1.json"`
`specVersion`	string	yes	Must be `"1.0"`
`generated`	string	no	ISO 8601 timestamp of when the document was generated
`generator`	string	no	Identifier of the tool that produced the document
`apps`	array	yes	One or more application entries

App Entry

Each element of the apps array describes a single application. Localized fields at the app level are shared defaults across all platforms.

Field	Type	Required	Description
`name`	string	yes	Canonical machine-readable name
`title`	localized string	no	Display name (shared across platforms)
`subtitle`	localized string	no	Short promotional text
`description`	localized string	no	Full description
`keywords`	localized string array	no	Search keywords as arrays
`releaseNotes`	localized string	no	What’s new in this version
`platforms`	object	yes	Per-platform metadata (keys are platform identifiers)
`links`	object	no	Cross-platform URLs (privacy, support, etc.)
`source`	object	no	Source code repository information

Field Promotion and Resolution

When a localized field (title, subtitle, description, keywords, releaseNotes) is identical across all platforms, the generator promotes it to the app level to avoid duplication. When it differs between platforms, each platform carries its own version.

Resolution rule for consumers: When a promotable field exists at both the app level and a platform level, the platform-level value takes precedence for that platform. Consumers SHOULD resolve each locale by checking the platform first, then falling back to the app level.

When all locales of a localized string have the same value (e.g. a brand name that doesn’t change across languages), the value is collapsed to a single "en" key.

Platform Entry

Each key in platforms is a platform identifier (e.g. "ios", "android", "macos", "windows", "linux"). The platform identifier is the key in the parent object, not a field within the platform entry.

Field	Type	Required	Description
`version`	string	yes	Human-readable version string
`buildNumber`	string	no	Internal build number
`bundleIdentifier`	string	no	Apple bundle identifier (Apple platforms)
`applicationId`	string	no	Android application ID (Android platforms)
`title`	localized string	no	Platform-specific display name override
`subtitle`	localized string	no	Platform-specific promotional text override
`description`	localized string	no	Platform-specific description override
`keywords`	localized string array	no	Platform-specific keywords override
`releaseNotes`	localized string	no	Platform-specific release notes override
`permissions`	array	no	Permission declarations
`channels`	object	no	Distribution channel entries
`assets`	object	no	Image assets (icon, screenshots, etc.)
`metadata`	object	no	Platform-specific configuration (opaque)
`sbom`	object	no	SPDX 2.3 Software Bill of Materials

Localized Strings

All user-facing text is represented as a localized string: an object mapping BCP 47 ↗ locale codes to translated values. The "en" key represents the default English locale.

{ "en": "A fast web browser", "fr": "Un navigateur web rapide" }

When all locales have the same value, the dictionary is collapsed to a single "en" key.

Keywords use a localized string array format:

{ "keywords": { "en": ["web", "browser"], "fr": ["web", "navigateur"] } }

Links

Cross-platform URLs. Each value is a localized URL map:

{ "links": { "privacy": { "en": "https://example.com/privacy" } } }

Source Repository

{
  "source": {
    "url": "https://github.com/Org/App.git",
    "release": "https://github.com/Org/App/releases/tag/1.0.0/",
    "assets": "https://raw.githubusercontent.com/Org/App/refs/tags/1.0.0/",
    "license": "GPL-2.0-only"
  }
}

Field	Description
`url`	Repository clone URL (may be HTTPS or SSH; intentionally not URI-constrained)
`release`	URL to the release page for the current version
`assets`	Base URL for resolving image `location` paths: `assets + location` = full URL
`license`	SPDX license identifier

Distribution Channels

Each platform declares distribution channels in the channels object. Keys are channel identifiers. Well-known keys include appleappstore, googleplaystore, fdroid, altstore, testflight, amazonappstore, homebrew, flatpak, and microsoftstore.

{ "channels": { "appleappstore": { "id": "1640618584", "url": "https://apps.apple.com/app/id1640618584" } } }

Assets

Image assets grouped in an assets object:

{
  "assets": {
    "icon": { "location": "icon-1024.png", "size": 442604, "digest": "sha256:bea1...", "width": 1024, "height": 1024 },
    "screenshots": { "en": [{ "location": "screenshots/1.png", ... }] },
    "featureGraphic": { "en": { "location": "images/featureGraphic.png", ... } }
  }
}

Image location paths combined with source.assets form resolvable URLs.

Permissions

Platform-specific declarations with a key and an optional localized description:

{ "permissions": [{ "key": "NSCameraUsageDescription", "description": { "en": "Camera access for video calls" } }] }

Platform Metadata

Opaque platform-specific configuration in the metadata object:

{ "metadata": { "entitlements": { ... }, "infoPlist": { ... }, "manifest": { ... } } }

Generation

skip meta index                          # stdout
skip meta index -O appindex.json         # file
skip export --appindex -d output/        # export with resource linking

Schema

https://appfair.org/schemas/appindex/v1.json ↗