I Built a 21K-Line Android Scanner App in One Day — Here's the Full Template

# android# kotlin# mobile# jetpackcompose
I Built a 21K-Line Android Scanner App in One Day — Here's the Full TemplateA Bit Above Bytes

Every document scanner app on the Play Store looks the same. They all use CameraX, ML Kit, and Room —...

Every document scanner app on the Play Store looks the same. They all use CameraX, ML Kit, and Room — yet developers keep rebuilding the same architecture from scratch.

So I built the template once, properly, and I'm sharing the full source.

What's Inside

92 Kotlin files. 21,000+ lines. Production-ready architecture.

  • Scanner Engine — CameraX + ML Kit Document Scanner with auto-capture, frame stability detection, 6 scan modes (Document, ID Card, Passport, Receipt, Whiteboard, Book)
  • PDF Engine — Generate, merge, split PDFs with invisible OCR text layer at 300 DPI. No iText dependency (avoids AGPL licensing headaches)
  • OCR — ML Kit Text Recognition v2 with bounding box positioning, background processing via WorkManager
  • eSign — Draw, type, or upload signatures. Composite onto document pages
  • Monetization — RevenueCat integration with metered paywall (soft prompt at scan 2, hard gate at limit), 4 A/B test paywall variants, weekly + annual plans
  • Full UI — Material 3 + Jetpack Compose. Dark onboarding flow, animated paywall, bottom navigation, document grid/list views

Architecture 

data/          → Room DB (5 entities, 5 DAOs), Repository pattern, DataStore prefs
domain/        → Use cases, engine layer (Scan, PDF, OCR, eSign, Barcode)
ui/            → 15+ screens, Compose navigation, Hilt DI
service/       → WorkManager workers for background OCR + PDF export
util/          → Analytics, RevenueCat config, A/B testing via Firebase Remote Config
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Clean Architecture with proper separation. Not a tutorial project — this is what you'd actually ship.

The Stack

Layer Tech
Language Kotlin 2.0
UI Jetpack Compose + Material 3
Camera CameraX 1.4
ML ML Kit (Document Scanner, Text Recognition, Barcode)
Database Room 2.6
DI Hilt
Payments RevenueCat
Analytics Firebase Analytics + Crashlytics + Remote Config
Background WorkManager
Security AES-256-GCM encryption, Biometric lock

Why I Built This

I kept seeing the same pattern: developers spend 2-3 months building scanner app infrastructure before they can even start on their unique features. Edge detection, perspective correction, OCR positioning, PDF generation with text layers, paywall flows — it's all solved problems, but the implementation details eat your time alive.

This template handles the 80% that's identical across every scanner app, so you can focus on what makes yours different.

What You Can Build With It

  • Receipt scanner for expense tracking
  • Business card scanner with CRM integration
  • Medical document organizer
  • Construction site documentation tool
  • Legal document management app
  • Student note digitizer

Rebrand it, customize the UI, add your domain-specific features, and ship.

Get It

The full template is available here: ScanVault Pro Template on Gumroad

Includes complete source code, architecture docs, customization guide, and a quick-start walkthrough.

Happy to answer any questions about the architecture decisions or implementation details in the comments.