Kotlin Symbol Processing (KSP): Complete Guide with Examples

1. What is KSP and Why Use It?

Kotlin Symbol Processing (KSP) is a library and compiler plugin for the Kotlin language, developed by JetBrains. Its primary goal is to provide developers with a simple, fast, and reliable API for analyzing Kotlin source code at compile time and generating new code (code generation) based on that analysis. KSP is a direct alternative to the older javax.annotation.processing (Java Annotation Processing) mechanism, which was designed for Java and has several limitations when working with Kotlin.

Why do you need KSP? In modern Kotlin development, you often need to automatically generate boilerplate code: DTO classes, mappers, Parcelable implementations, Room entities, Moshi adapters, and much more. KSP lets you do this at compile time, without runtime reflection, which boosts application performance. Unlike KAPT (Kotlin Annotation Processing Tool), KSP works directly with Kotlin's AST tree, bypassing the intermediate Java stage, resulting in a 2–4x speed increase. KSP also has better support for newer Kotlin language features (suspend functions, inline classes, value classes) and doesn't require generating Java stubs.

KSP is ideal for building your own code generation libraries, frameworks (similar to Dagger, Room, Glide), and metaprogramming tools. It's actively used in the Kotlin ecosystem: Compose, Room, Moshi, Koin, Apollo GraphQL, and many other popular libraries.

2. Setup

KSP is not installed via pip or npm; it's added through the Gradle build system. For a Kotlin project, you need to add the KSP plugin and its version, which must match your Kotlin version.

Exact command to add to build.gradle.kts (root project):

// build.gradle.kts (root level)
plugins {
    id("org.jetbrains.kotlin.jvm") version "1.9.22" apply false
    id("com.google.devtools.ksp") version "1.9.22-1.0.17" apply false
}

// build.gradle.kts (app module)
plugins {
    id("org.jetbrains.kotlin.jvm")
    id("com.google.devtools.ksp")
}

dependencies {
    implementation("org.jetbrains.kotlin:kotlin-stdlib:1.9.22")
    implementation("com.squareup:kotlinpoet:1.16.0") // for code generation
    ksp("com.example:my-processor:1.0.0") // your processor
}

For Gradle Groovy (build.gradle):