KSP vs KAPT

Learn the difference between KSP and KAPT.

KSP vs KAPT

KSP and KAPT both generate code at compile time, but they take different paths. KSP reads Kotlin symbols directly; KAPT first converts Kotlin to a Java stub.

KSP is up to 2x faster; it supports Kotlin-specific constructs (suspend functions, inline classes) better. KAPT is older and more common; legacy libraries like Dagger still require KAPT. When starting a new project, prefer KSP; if a dependency forces KAPT, plan a migration. Both generate code at compile time; neither has runtime cost.

Migration plan

Migrating from KAPT to KSP is often simple: in the Gradle file, replace kapt with ksp and update dependencies.

Example: instead of kapt("com.example:processor:1.0") write ksp("com.example:processor:1.0"). With Kotlin 2.x the kapt plugin still works, but KSP is preferred. If a dependency does not offer KSP, keep KAPT temporarily; once the library adds KSP support, remove it fully. This keeps the project working.

Exercise Write the comparison table

Define data class Tool(val name: String, val factor: Int). In main, build listOf(Tool("KSP", 1), Tool("KAPT", 3)). For each tool, write println("${'$'}{it.name}: ${'$'}{it.factor}x").

Show example solution

data class Tool(val name: String, val factor: Int)
fun main() {
    val tools = listOf(Tool("KSP", 1), Tool("KAPT", 3))
    tools.forEach { println("${it.name}: ${it.factor}x") }
}

Test yourself

Which one is faster?
- KAPT, because it uses Java
- KSP, because it reads Kotlin directly
- It depends on the library
- Both are equally fast
Show answer

KSP, because it reads Kotlin directly — KSP is faster because it reads Kotlin symbols directly.

Write KSP speed

val ksp = 1
val kapt = ____
println("KSP ${ksp}x, KAPT ${kapt}x")

Show answer

val ksp = 1
val kapt = 3
println("KSP ${ksp}x, KAPT ${kapt}x")

Match KSP/KAPT

KSP

Reads Kotlin directly
KAPT

Converts to Java stub
ksp(...)

KSP dependency
kapt(...)

KAPT dependency

Next lesson: Generated code

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