koruDocumentation
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koru, Capacitor and Expo

Capacitor and Expo are mature, widely used tools. koru does much less, on purpose. This page helps you decide which one fits your project.

On this page

The short version

  • Choose koru when you have a web app, you only need Android, and you want a tiny toolchain: one Go binary that builds a signed APK offline in milliseconds, with no Java, Gradle or Android SDK.
  • Choose Capacitor when your web app needs iOS as well as Android, a large plugin ecosystem, Google Play bundles (AAB) or native code you write in Kotlin, Java or Swift.
  • Choose Expo when you want to write the app in React Native, with native UI components, iOS and Android, over-the-air updates and cloud builds.

Side by side

koru Capacitor Expo
You write HTML, CSS, JavaScript; any static frontend HTML, CSS, JavaScript; any web framework React Native (JavaScript/TypeScript)
UI renders in Android System WebView WebView (Android, iOS) Native views
Android build needs The koru binary only Android Studio or Gradle, JDK, Android SDK EAS Build (cloud), or JDK and Android SDK locally
Platforms Android Android, iOS, web Android, iOS, web
Output Signed APK (v2) APK, AAB APK, AAB
Start a project koru create: basic, Vite, React, Vue, Svelte or TypeScript templates npm init @capacitor/app npx create-expo-app
Preview while coding koru dev: browser, live reload, web implementations of the API Your framework’s dev server; live reload on device via server.url Expo Go or a development build, with fast refresh
Run on a device koru run npx cap run android npx expo run:android
Device logs koru logs in your terminal (not yet validated on a device) Android Studio Logcat, or chrome://inspect for the WebView Terminal and dev tools while the dev server runs
Deep links deepLinks in koru.json; opens the app, URL not passed to JavaScript yet; untested on Android Supported, including the URL in JavaScript (App plugin) Supported through Expo Router and linking
Versioning koru bump, koru build --bump Edit Gradle or Xcode project files version in app config; EAS can auto-increment
Native features 6 built-in plugins; custom plugins as DEX manifests or JNI libraries Official and community plugins; write your own natively Expo SDK modules; write your own natively
Maturity Experimental; recorded on Android 11 (API 30) x86_64 Widely used in production Widely used in production

What koru does differently

No native toolchain. koru writes the DEX bytecode, binary manifest, resource table, ZIP and APK signature itself in Go. A build does not download anything or start a JVM, so it is fast and works offline. The trade-off is that you cannot add arbitrary Java or Kotlin code: custom plugins are described as DEX intermediate representation, or call a prebuilt JNI library.

A small, strict runtime. Your files are served from a private HTTPS origin, https://app.koru.invalid, and the JavaScript bridge is a MessagePort bound to that origin. There is no addJavascriptInterface. Network access is off unless you add the Internet permission.

The same API in the browser. Like Capacitor’s web implementations, koru’s JavaScript API runs in a desktop browser during koru dev, so you can build most of the app before installing it.

What koru does not do yet

  • iOS apps.
  • Android App Bundles (AAB) for Google Play. koru produces APKs for direct installation and stores that accept APKs.
  • Pass a deep link’s URL to your JavaScript. The link opens the app on its first page, and neither the verified-link flow nor any of this has been run on Android.
  • Exact alarms (the alarms plugin is inexact and not yet tested on a device), push notifications and plugins outside the ten built-in ones. Camera, geolocation, microphone and file pickers are not plugins: with the webFeatures option your pages use the web APIs, tested in Chromium but not yet on an Android device; see Files, location, camera and microphone.
  • Live reload inside the installed APK. Use koru dev in a browser, then koru run. koru can load a published HTTPS page with server.url, but that is not live reload of your local files; see Remote content.
  • Verified execution beyond the recorded matrix.

If you need those today, Capacitor or Expo are the better choice. If you need a small, auditable Android toolchain for a web app, try koru: create your first app.

Capacitor and Expo change quickly; check their Capacitor and Expo documentation for current details.