Codebase Tour Checklist

A tiered checklist for where routes, features, native config, and CI live in an Expo SDK 57 app - use on day two with a buddy, not as a solo scavenger hunt.

How to Use This Checklist

• Complete Tier 1 before your first PR; Tier 2 before capstone feature; Tier 3–4 in week two.
• Replace placeholder paths (features/orders/) with your repo's real names - grep if README is stale.
• Mark each item ✓ found, ? unclear, or ✗ missing - escalate ✗ to platform lead.
• Record answers in your onboarding PR or internal wiki - the next hire inherits your notes.
• Re-run Tier 4 when joining a new squad or after a major architecture migration.

Tier 1 - Day One (1–8)

You can run Metro and find the home screen without asking Slack.

1. Repository entry README - clone command, Node version, npm ci vs pnpm, link to Slack channels.

   • Look for: engines.node, #mobile or #app channel, link to EAS project
   • Ask if missing: "Where is the canonical getting-started doc?"

2. package.json scripts - how lint, typecheck, test, and start are invoked.

   • Look for: expo start, typecheck, lint, test - same scripts CI calls
   • Related: Project Setup Basics

3. SDK pin - expo, react, react-native versions match SDK 57 matrix.

   • Look for: "expo": "~57.0.4", "react": "19.2.3", "react-native": "0.86.0"
   • Verify: npx expo-doctor passes on clean clone

4. app/ directory - file-based routes (Expo Router).

   • Look for: _layout.tsx, index.tsx, (tabs)/ or route groups
   • Rule: Route files stay thin - re-export feature screens
   • Related: Expo Router Basics

5. Root layout app/_layout.tsx - providers, fonts, splash, root navigator.

   • Look for: QueryClient, theme, auth gate, Stack / Tabs from expo-router
   • Signal: All global wrappers should be here or one imported provider file

6. app.config.ts or app.json - bundle IDs, icons, plugins, extra for env.

   • Look for: ios.bundleIdentifier, android.package, plugins: [], extra.eas.projectId
   • Related: Project Setup Basics

7. Environment template - .env.example with EXPO_PUBLIC_* vars documented.

   • Look for: Staging API URL, feature flag keys safe for client bundle
   • Never: Private API secrets in EXPO_PUBLIC_

8. CONTRIBUTING.md - branch flow, commit style, PR template, preview build label.

   • Look for: needs-preview label rules, CODEOWNERS mention, conventional commits

Tier 2 - First PR (9–16)

You can trace one user action from tap to network.

9. Feature folder convention - where screen logic lives outside app/.

   • Look for: features/<name>/screens|hooks|api|components/
   • Alt patterns: src/modules/, FSD entities/ + features/
   • Related: Folder Structure for Features

10. Shared API client - single HTTP wrapper with auth headers and base URL.

    • Look for: shared/api/client.ts, lib/api.ts, or createApiClient() factory
    • Trace: Screen → hook → ordersApi.getById → client.get

11. Auth/session gate - how signed-out users are redirected.

    • Look for: Redirect in app/_layout.tsx, (auth)/ route group, or useAuth() guard
    • Ask: Where is refresh token stored? (expo-secure-store pattern)

12. State strategy - what lives in TanStack Query vs Zustand vs context.

    • Look for: useQuery for server data; store only for UI session state
    • Smell: fetch inside Zustand actions duplicating query cache

13. Design system entry - buttons, typography, theme tokens.

    • Look for: shared/ui/, @/components, or external package import
    • Ask: Storybook or on-device catalog URL if it exists

14. eas.json build profiles - development, preview, production.

    • Look for: developmentClient, distribution: internal, channel per profile
    • Related: EAS Build Basics

15. TypeScript paths - @/ alias mapping in tsconfig.json.

    • Look for: "paths": { "@/*": ["./*"] }" or monorepo package names
    • Verify: Jump-to-definition from route to feature screen works in IDE

16. Test colocation - *.test.tsx beside components or __tests__ folder policy.

    • Look for: jest.config.js, jest.setup.ts, jest-expo preset
    • Run: npm test -- --listTests | head

Tier 3 - Week Two (17–24)

You can reason about native behavior and debug production-shaped builds.

17. Config plugins - native changes without hand-editing ios/ / android/.

    • Look for: plugins: ["expo-router", "./plugins/withCustom"] in app config
    • Ask: When was last npx expo prebuild and is CNG adopted?

18. ios/ and android/ presence - managed vs bare vs generated native dirs.

    • Managed/CNG: folders gitignored - EAS generates at build
    • Bare: folders committed - local pod install required
    • Related: Prebuild Basics

19. Deep linking config - scheme, universal links, intent filters.

    • Look for: scheme in app config, apple-app-site-association, Android intent filters
    • Related: Deep Linking Basics

20. Push notifications wiring - token registration and cold-start route.

    • Look for: expo-notifications setup, app/_layout.tsx notification response listener
    • Ask: Which environment sends test pushes?

21. Analytics and error reporting - Sentry, Datadog, Amplitude, etc.

    • Look for: init in root layout or AppProviders, captureException usage pattern
    • Ask: PII rules - what is forbidden in breadcrumbs?

22. OTA updates - channels and runtimeVersion policy.

    • Look for: expo-updates config, eas update channel names in docs
    • Related: OTA Updates Basics

23. Maestro / E2E folder - smoke flows and when CI runs them.

    • Look for: .maestro/smoke.yml, appId matching bundle identifier
    • Related: Mobile Testing Basics

24. Internationalization - locale files and date/number formatting.

    • Look for: i18n/, locales/, expo-localization usage
    • Smell: Hard-coded strings in feature screens without extraction

Tier 4 - Release Literacy (25–30)

You know how code becomes a store binary and who to ping when it breaks.

25. CI workflow location - GitHub Actions, GitLab CI, or EAS Workflows.

    • Look for: .github/workflows/pr-checks.yml, .eas/workflows/
    • Trace: PR open → which jobs run → required checks for merge

26. PR vs release pipelines - separate triggers and secrets.

    • Look for: pull_request for lint/tsc/test; tags: v* for eas build
    • Related: Mobile CI/CD Basics

27. EXPO_TOKEN and secrets docs - where robot credentials live (not in repo).

    • Look for: GitHub org secrets runbook, 1Password vault name
    • Never: Tokens in workflow YAML plaintext

28. Store submission path - who runs eas submit and TestFlight / Play tracks.

    • Look for: submit profile in eas.json, internal testing doc links
    • Related: EAS Submit

29. Monorepo boundaries - if applicable, which workspace is the mobile app.

    • Look for: apps/mobile/, packages/ui, turbo.json pipeline filters
    • Related: Monorepo with Turborepo

30. CODEOWNERS and on-call - who must approve app/, native, or release changes.

    • Look for: .github/CODEOWNERS, PagerDuty / on-call schedule link
    • Ask: Hotfix process outside business hours

Tour Session Template

Use this 60-minute agenda with a buddy:

## Codebase tour - <hire> + <buddy> - <date>
 
### Tier 1 (20m)
- [ ] README clone path verified
- [ ] app/_layout.tsx walked
- [ ] app.config.ts bundle IDs noted
 
### Tier 2 (25m)
- [ ] Traced: <pick one feature> tap → API
- [ ] eas.json profiles explained
- [ ] Test command run together
 
### Tier 3–4 (15m sketch)
- [ ] CI PR checks named
- [ ] Preview build label demonstrated
- [ ] Open questions logged below
 
### Open questions → doc PRs
1.
2.

FAQs

Related

• Onboarding Basics - machine setup before the tour
• First-Week Learning Path - capstone feature arc
• Project Setup Basics - default SDK 57 layout
• Expo Router Basics - app/ routing
• EAS Build Basics - build profiles
• Mobile CI/CD Basics - PR vs release pipelines

Stack versions: This page was written for React 19.2.3, React Native 0.86.0, and Expo SDK 57 (expo ~57.0.4).