Set up a project

An extension is an ordinary Android app project. Build it with JDK 21, the Android SDK and the Gradle 9.4 wrapper, and put its code in src/main/kotlin.

pluginManagement {
    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}

dependencyResolutionManagement {
    repositories {
        google()
        mavenCentral()
        maven("https://jitpack.io")
    }
}

rootProject.name = "example-comics"

android.useAndroidX=true
kotlin.stdlib.default.dependency=false

plugins {
    id("com.android.application") version "8.13.2"
    id("org.jetbrains.kotlin.android") version "2.3.20"
    id("org.jetbrains.kotlin.plugin.serialization") version "2.3.20"
}

android {
    namespace = "org.example.katari.examplecomics"
    compileSdk = 36

    defaultConfig {
        applicationId = "org.example.katari.examplecomics"
        minSdk = 29
        targetSdk = 36
        versionCode = 1
        versionName = "4.0.0"
    }

    compileOptions {
        sourceCompatibility = JavaVersion.VERSION_17
        targetCompatibility = JavaVersion.VERSION_17
    }
}

kotlin {
    compilerOptions {
        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17)
    }
}

dependencies {
    compileOnly("com.github.pa2x2.katari:entry-source-api:sdk-4.0.0")
}

• Keep the SDK compileOnly, and the libraries below too if you name them yourself, so the APK holds only your own code. Katari supplies all of them.
• kotlin.stdlib.default.dependency=false leaves Kotlin's standard library out of the APK as well. Katari always loads kotlin.* from its own copy, so a bundled one would only take space.
• Katari runs on Android 10 and newer, which is API level 29, and on Linux, where it converts the same APK.

Katari's release build keeps these libraries for extensions, in the versions of the current release:

The SDK brings the first two, JSON, OkHttp, Okio, Jsoup, Injekt, RxJava and Preference to your compile classpath. Add Protobuf or kotlinx-datetime yourself with compileOnly, in the version above or older.

Of the SDK itself, use eu.kanade.tachiyomi.source.*, eu.kanade.tachiyomi.network.* and app.katari.book.api.*. Its other packages, and libraries it depends on but that aren't listed above, such as logcat, are Katari's own code: they compile, but its release build may have removed or changed them, and the extension then fails with NoClassDefFoundError or NoSuchMethodError only in users' copies of Katari. On Linux, an Android class or member Katari doesn't provide there shows as Not on desktop yet instead. Log with android.util.Log.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">

    <uses-feature android:name="tachiyomi.extension" />

    <application
        android:allowBackup="false"
        android:icon="@mipmap/ic_launcher"
        android:label="Katari: Example Comics">

        <meta-data
            android:name="tachiyomi.extension.class"
            android:value=".ExampleComicsFactory" />

        <meta-data
            android:name="tachiyomix.contentWarning"
            android:value="0" />
    </application>
</manifest>

An exception thrown while creating any of the classes leaves the whole extension under Not loaded, as What users see before it runs lists.

• versionName is the SDK's major and minor, then your own release number: 4.0.0, 4.0.1 and so on. When you move to a newer SDK, start that one's count at 0.
• versionCode goes up by one with every release you publish. Stores offer an update when it grows, or when the listing is built with a newer SDK. Android refuses to install a lower one, and a user's Trust holds for one version code.
• applicationId never changes once published. It is how Android and Katari know a new APK updates the old one; another ID installs as a second extension.

1. Build the debug APK and install it with a phone connected:

   ./gradlew assembleDebug
   adb install build/outputs/apk/debug/example-comics-debug.apk

2. Open Browse › Extensions. The extension is listed as Untrusted; tap the shield and Trust.
3. Its sources appear under Browse › Sources.

If the extension is already installed from a store, Android refuses a copy signed with another key, so uninstall that one first. With Private picked as the installer, Katari keeps both copies and uses the one with the higher versionCode, and yours on a tie. If it lands under Not loaded instead, tap the info button for the reason, as What users see before it runs lists. An exception a source throws shows as an error where the user was, such as on the source's list or the title's page, and Katari logs most of them with their stack trace to adb logcat.