Kotlin Symbol Processing API

Welcome to KSP!

Kotlin Symbol Processing (KSP) is an API that you can use to develop lightweight compiler plugins. KSP provides a simplified compiler plugin API that leverages the power of Kotlin while keeping the learning curve at a minimum. Compared to KAPT, annotation processors that use KSP can run up to 2x faster.

Most of the documentation of KSP can be found on kotlinlang.org. Here are some handy links:

• Overview
• Quickstart
• Libraries that support KSP
• Why KSP?
• Examples
• How KSP models Kotlin code
• Reference for Java annotation processor authors
• Incremental processing notes
• Multiple round processing notes
• KSP on multiplatform projects
• Running KSP from command line
• FAQ

For debugging and testing processors, as well as KSP itself, please check DEVELOPMENT.md

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KSP Gradle Configurations Reference

This section contains a reference of Gradle configurations for KSP. If you have not used KSP before, or this section seems unclear, please read the documentation on the Kotlin lang website which is linked above.

When applying KSP in your Gradle project, place symbol processor dependencies into the appropriate configuration inside the dependencies { ... } block of your build.gradle.kts (or build.gradle) file based on your target platforms, source sets, and build variants.

Single-Platform (JVM & Android)

Configuration Name / Pattern	Project Type / Target	Source Set / Scope	Usage Example (build.gradle.kts)	Details & Behavior
ksp	Single-target JVM / Android	Main source set (src/main)	ksp("com.example:processor:1.0")	Applied to default JVM compilation and single-platform Android main source set. Deprecated in KMP unless ksp.allow.all.target.configuration=true.
kspTest	Single-target JVM / Android	Unit tests (src/test)	kspTest("com.example:test-processor:1.0")	Runs symbol processing exclusively for unit test sources.
ksp<SourceSet>	Single-target JVM	Custom JVM source set	add("kspIntegrationTest", "...")	Generates sources for custom source sets like integrationTest.
ksp<BuildType>	Android (Single-platform)	Specific build type (e.g., debug, release)	add("kspDebug", "...")	Runs processor only when compiling the specified Android build variant.
ksp<Flavor>	Android (Single-platform)	Product flavor (e.g., free, paid)	add("kspFree", "...")	Runs processor for all build variants matching the specified flavor.
ksp<Flavor><BuildType>	Android (Single-platform)	Flavor + Build Type combination	add("kspFreeDebug", "...")	Targeted execution for a specific flavor + build type variant.
kspTest<Flavor><BuildType>	Android (Single-platform)	Local Unit Tests for variant/flavor	add("kspTestDebug", "...")	Runs processing on unit test code in src/testDebug.
kspAndroidTest<Variant>	Android (Single-platform)	Instrumentation Tests (src/androidTest)	add("kspAndroidTestDebug", "...")	Runs processing on Android instrumentation test code (src/androidTest).

Kotlin Multiplatform (KMP)

Configuration Name / Pattern	Project Type / Target	Source Set / Scope	Usage Example (build.gradle.kts)	Details & Behavior
ksp<Target>	Kotlin Multiplatform	KMP target main compilation (JVM, JS, Native, Wasm)	add("kspJvm", "...") add("kspJs", "...") add("kspIosArm64", "...") add("kspAndroid", "...") add("kspAndroidHostTest", "...") add("kspAndroidDeviceTest", "...")	Target-specific configuration. Omits the Main suffix (e.g., target jvm becomes kspJvm, not kspJvmMain).
ksp<Target>Test	Kotlin Multiplatform	KMP target test compilation	add("kspJvmTest", "...") add("kspJsTest", "...")	Target-specific test configuration.
kspCommonMainMetadata	Kotlin Multiplatform	Common Main metadata compilation	add("kspCommonMainMetadata", "...")	Target-specific configuration for KMP commonMain metadata processing.

KSP Gradle Properties Reference

This section provides a reference of Gradle properties for KSP. These properties can be set in your project's gradle.properties file or passed via command line options (-Pproperty=value or -Dproperty=value).

Reference Table

Property Key	Type	Default	Description	Documentation
ksp.incremental	Boolean	true	Enables or disables incremental symbol processing in KSP.	Incremental Processing
ksp.incremental.log	Boolean	false	Enables verbose log output detailing incremental processing decisions and symbol changes.	Incremental Logging
ksp.incremental.log.graph.origin	String?	null	Filters incremental log tracing to a specific symbol origin class/package. The value should be of the form com.example.MyClass.	Incremental Dependency Graph
ksp.allow.all.target.configuration	Boolean	false	Permits the legacy global ksp configuration in both single-platform and Kotlin Multiplatform (KMP) projects with a warning instead of an error.	ksp Configuration
ksp.project.isolation.enabled	Boolean	false	Enables Gradle Project Isolation compatible codepaths for output directory registration. NOTE: KSP also enables this if you have org.gradle.unsafe.isolated-projects=true configured.	Gradle Isolated Projects
ksp.experimental.psi.resolution	Boolean	false	Enables experimental PSI-based resolution inside the KSP compiler engine. Enabling this may improve build times, but expect crashes. Feel free to open a bug report if you encounter a crash.	None
ksp.ksp2.profiling.mode	Boolean	false	Enables performance profiling for KSP2 task execution. This is mostly for developing KSP itself.	None
kotlin.native.enableKlibsCrossCompilation	Boolean	true	Enables running symbol processing tasks for other targets than the host machine in KMP projects, i.e., cross-compilation. This property is not created by the KSP Gradle plugin. It is owned by the Kotlin compiler but KSP uses this property.	Kotlin Cross Compilation

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Nightly Builds

Nightly builds of KSP for the latest Kotlin stable releases are published here:

maven("https://central.sonatype.com/repository/maven-snapshots/")

Feedback and Bug Reporting

Please let us know what you think about KSP by filing a Github issue or connecting with our team in the #ksp channel in the Kotlin Slack workspace!

If you are interested in sending PRs, please also check out the Contributor guide.

Ongoing and Future Work

Here are some planned features that have not yet been completely implemented:

• Improve support to multiplatform. E.g., running KSP on a subset of targets / sharing computations between targets
• Improve performance. There are a bunch of optimizations to be done!
• Keep fixing bugs!

A Note on KSP1

KSP 1.x has been removed and is no longer supported.