Kern

A privacy-first, fully offline, open-source Android document toolkit. No cloud sync. No data collection. No network access. Completely free. AGPL-3.0.

Kern is in early alpha.

What Kern does

Kern integrates with Android's "Open with" system, so any file on your device - in Downloads, Documents, or anywhere else - can be opened directly in Kern. There is no separate app folder and no syncing. Kern reads and writes files in place; your files stay yours, on your device.

Document formats

Kern works with common document types:

• Spreadsheets - .xlsx, .xls, .csv
• Documents - .docx
• Presentations - .pptx
• PDF - .pdf
• EPUB - .epub

Tech stack

• Language: Kotlin + Jetpack Compose
• Office formats: Apache POI (xlsx, docx, pptx) + OpenCSV
• PDF engine: MuPDF via the Qyra Rust JNI/NDK bridge (GPL-3.0)
• License: AGPL-3.0
• Min Android API: 26 (Android 8.0+)

Permissions

Kern requests:

• READ_EXTERNAL_STORAGE / WRITE_EXTERNAL_STORAGE (older Android versions)
• READ_MEDIA_* (Android 13+)
• MANAGE_EXTERNAL_STORAGE - guided toward Documents and Downloads
• "Open with" intent filters for supported document types

No network permissions. Ever.

Project structure

kern/
├── src/
│   ├── browser/          # File browser + "Open with" intent handling
│   ├── editors/          # One module per format (csv, excel, word, pdf, pptx)
│   ├── pdf-bridge/       # Native PDF bridge (JNI/NDK)
│   └── shared/           # Theme, shared UI, utilities
├── res/                  # Android resources (launcher icon, themes, strings)
├── tests/                # Mirrors src/ structure
├── docs/                 # Architecture notes
├── brand/                # Logo assets
├── config/               # Lint configuration
├── scripts/              # Dev tooling
└── sample-files/         # Sample documents

Versioning

This project uses an A.B.C.D version scheme. Released versions are tagged in git: the current version is whatever the version badge above shows (see the tags).

Getting started

git clone https://github.com/verycareful/kern.git

Open the folder in Android Studio and press Run. Studio provisions the matching Gradle version (8.10.x, pinned in gradle/wrapper/gradle-wrapper.properties) automatically. Prebuilt debug APKs are also attached to each GitHub Release and to the CI run artifacts.

See docs/architecture.md for system design and CONTRIBUTING.md for contributor guidelines.

License

AGPL-3.0. See LICENSE.

PDF engine: MuPDF via Qyra (GPL-3.0, compatible with AGPL-3.0).