SNI Checker

Fast Android utility for checking SNI host availability over TLS and collecting working domains into exportable result files.

SNI Checker is built for large domain lists, responsive scanning, and low APK size. The app uses a minimal Jetpack Compose UI, bounded concurrency, batched UI updates, and optimized APK packaging.

Features

• Checks SNI domains through TLS connections on port 443
• Supports local .txt lists and remote URL sources
• Saves results to an easy-to-access public folder: /sdcard/Download/SniChecker/
• Sorts working SNI domains by ping/RTT
• Exports:
  • results.json
  • working_sni.txt
  • working_sni_sorted_by_rtt.txt
• Minimal high-performance UI designed to reduce scroll jank and frame drops
• Fast stop behavior: active sockets are closed when scanning is stopped
• Optimized APK size, around 1.1 MB for the current debug/release builds

Screenshots

Add screenshots or a short demo GIF here after publishing the first release.

Requirements

• Android 7.0+ (minSdk 24)
• Android SDK / Android Studio
• JDK 17
• Internet access on the device
• File access permission for reading lists and writing reports

Permissions

The app requests:

• INTERNET - required for TLS checks and downloading remote SNI lists
• ACCESS_NETWORK_STATE - used to inspect network availability
• Storage permissions / All files access - required to read input files and write reports under /sdcard/Download/SniChecker/

On Android 11+, the app opens the system settings screen so the user can grant All files access manually. Android does not allow apps to grant this permission automatically.

Default Storage Layout

/sdcard/Download/SniChecker/
|-- sni.txt
|-- web_cache/
`-- scan_out/
    |-- results.json
    |-- working_sni.txt
    `-- working_sni_sorted_by_rtt.txt

Input Format

Use one domain per line:

example.com
cloudflare.com
https://domain.com/path
domain.com:443

Blank lines and lines starting with # are ignored. URLs and ports are normalized to plain hostnames before scanning.

Build

Clone the repository:

git clone https://github.com/itachicoders/SNI_Checker.git
cd SNI_Checker

Build the APK:

./gradlew :app:assembleDebug

Build release APK:

./gradlew :app:assembleRelease

Generated APKs:

app/build/outputs/apk/debug/app-debug.apk
app/build/outputs/apk/release/app-release.apk
app/build/outputs/apk/release/app-release-unsigned.apk

If release signing credentials are configured, Gradle produces a signed release APK. Without signing credentials, release builds remain unsigned.

GitHub Actions

The repository includes a GitHub Actions workflow that builds APKs automatically on push, pull request, or manual dispatch.

Artifacts are available on the workflow run page:

• sni-checker-debug-apk
• sni-checker-release-apk

APK Signing

Debug builds are signed automatically by the Android Gradle Plugin.

Release signing is configured through environment variables, so private keys are not stored in the repository. For GitHub Actions, add these repository secrets:

• SIGNING_KEYSTORE_BASE64 - base64-encoded .jks or .keystore file
• SIGNING_KEYSTORE_PASSWORD
• SIGNING_KEY_ALIAS
• SIGNING_KEY_PASSWORD

Generate a release keystore:

keytool -genkeypair \
  -v \
  -storetype JKS \
  -keystore release.jks \
  -alias sni-checker \
  -keyalg RSA \
  -keysize 2048 \
  -validity 10000

Encode it for GitHub Secrets:

base64 -w 0 release.jks

On macOS:

base64 -i release.jks

When the secrets are present, GitHub Actions uploads a signed release APK artifact. When they are missing, the workflow still builds and uploads the unsigned release APK.

Performance Notes

The scanner is optimized to keep the UI responsive during heavy scans:

• Default concurrency is limited to 16
• Maximum concurrency is capped at 32
• Results are sent to the UI in batches
• Blocked domains are counted but not spammed into the visible terminal
• Active sockets are closed immediately on stop
• Output files are written with buffered IO

For older or low-end devices, keep concurrency between 8 and 16.

Tech Stack

• Kotlin
• Jetpack Compose
• Material 3 Compose
• AndroidX Lifecycle
• Kotlin Coroutines
• R8 / resource shrinking for small APK output

Security and Responsible Use

SNI Checker is intended for diagnostics, connectivity testing, and research on domains you are allowed to test. Use it responsibly and follow local laws, network policies, and service terms.

Roadmap

• Import file picker
• Share/export result files from inside the app
• Optional CSV export
• Scan history
• Dark/light theme toggle

License

This project is licensed under the MIT License - see the LICENSE file for details.