Mobile App Developer

mobile-app-developer

End-to-end playbook for shipping an Expo / React Native app — from scaffolding to TestFlight / Play Store — fully automated from a Linux sandbox.

When to Trigger

Trigger this skill when the user wants to:

• Scaffold or modify a React Native / Expo project
• Run / test / debug the app locally (Expo Go, dev client, simulator)
• Generate a web preview page with phone frame + Expo Go QR code
• Configure EAS Build (cloud build) for iOS or Android
• Publish to TestFlight (iOS internal testing) or Google Play Internal Testing
• Submit to App Store / Play Store public release
• Set up ASC API Key auth (bypass Apple 2FA)
• Replace icons / splash screens for store compliance
• Diagnose EAS build failures (peer deps, lock files, credentials, fingerprint, etc.)

Do NOT trigger for: pure native iOS/Android (no Expo), Flutter, Cordova/Capacitor, KMP/Compose Multiplatform.

Skill Layout

This skill is split into focused documents. Read the relevant one(s) on demand — do NOT preload all.

| File | Read when… | |---|---| | development.md | Setting up project, installing deps, configuring app.json, preparing icons/splash, running on simulator/device, fixing peer-dep / lock-file errors, managing env vars / secrets | | publishing.md | Configuring eas.json submit profile, ASC API Key / Play Service Account, running build + submit, diagnosing submit failures, App Store / Play Store metadata checklists | | preview.md | Generating a web preview page with phone frame + Expo Go QR code. Uses Expo Web (react-native-web) static export for browser preview and Expo dev server for real-device QR scanning |

If the user's task spans multiple (e.g. "build a new Expo app and ship it to TestFlight"), read development.md first, then publishing.md.

Default Tech Stack

| Layer | Choice | |---|---| | Framework | Expo (latest stable — check https://docs.expo.dev/versions/latest/ before scaffolding) | | Build / Distribution | EAS Build + EAS Submit (Expo cloud) | | Auth (Apple) | App Store Connect API Key (.p8) — bypasses 2FA | | Auth (Google) | Play Console Service Account JSON | | Auth (Expo) | Personal Access Token via EXPO_TOKEN |

Hard Preconditions

Before starting any build or publish work, confirm with the user:

• Expo account + EXPO_TOKEN (https://expo.dev/accounts//settings/access-tokens)
• For iOS:
• Apple Developer account (paid, $99/year)
• ASC API Key: .p8 file + Issuer ID + Key ID (role ≥ App Manager; ≥ Admin to create certs)
• Apple Team ID + ASC App ID + Bundle Identifier
• For Android:
• Google Play Console account ($25 one-time)
• Service Account JSON key (created in Play Console → API access)
• Package name + Play Console app already created
• First AAB must be uploaded manually to Play Console before automation works

If anything is missing, ask the user before proceeding. Do not guess.

Sandbox Requirements

The sandbox/CI must have:

node --version       # >= 18
npm --version        # >= 9
convert -version     # ImageMagick — for icon/splash conversion
expect -v            # for first-time non-interactive credential setup
curl --version       # for fetching build logs

Quick check:

for cmd in node npm convert expect curl; do
  command -v $cmd >/dev/null 2>&1 && echo "[OK] $cmd" || echo "[MISSING] $cmd"
done

If anything is missing, install before continuing (apt-get install imagemagick expect).

Architecture Recommendation

| Phase | AI/API key location | Why | |---|---|---| | Internal testing (TestFlight / Play Internal) | OK to call AI Gateway directly from client | Speed of iteration; risk is bounded by closed tester pool | | Public release | MUST proxy through your own backend | Embedded keys can be extracted from any IPA/AAB |

Useful URLs

• Expo SDK matrix: https://docs.expo.dev/versions/latest/
• EAS dashboard: https://expo.dev/accounts//projects//builds
• ASC API Keys: https://appstoreconnect.apple.com/access/integrations/api
• Play Console API access: https://play.google.com/console → Setup → API access
• Expo PAT: https://expo.dev/accounts//settings/access-tokens

Notes

• All commands tested on Linux. macOS users get extra options (local Xcode, simctl) which this skill avoids for portability.
• Treat .p8 files and Service Account JSONs like passwords. Always gitignore (*.p8, *-service-account.json).
• This skill assumes EAS cloud build. Local builds (expo prebuild + native toolchain) are out of scope.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: happycapy-ai
• Source: happycapy-ai/Happycapy-skills
• License: MIT

Install and usage instructions live in the source repository linked above.