> ## Documentation Index
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# Kotlin Retention Annotation
The `@Retention` meta-annotation determines the lifecycle of a custom annotation, specifically dictating whether the annotation is discarded during compilation, stored in the compiled binary, or made accessible to the reflection API during program execution.
In Kotlin, retention policies are defined by the `AnnotationRetention` enum, which provides three distinct levels of visibility:
* **`AnnotationRetention.SOURCE`**: The annotation exists only in the `.kt` source files. It is stripped out by the compiler and is entirely absent from the resulting `.class` files.
* **`AnnotationRetention.BINARY`**: The annotation is preserved in the compiled `.class` files but is not loaded into the JVM at runtime. It cannot be accessed via reflection. This is analogous to Java's `RetentionPolicy.CLASS`.
* **`AnnotationRetention.RUNTIME`**: The annotation is preserved in the compiled `.class` files and is loaded into the JVM, making it fully queryable at runtime using the Kotlin reflection API.
```kotlin theme={"dark"}
@Retention(AnnotationRetention.SOURCE)
annotation class SourceLevelAnnotation
@Retention(AnnotationRetention.BINARY)
annotation class BinaryLevelAnnotation
@Retention(AnnotationRetention.RUNTIME)
annotation class RuntimeLevelAnnotation
```
If a custom annotation is declared without an explicit `@Retention` meta-annotation, Kotlin implicitly applies `AnnotationRetention.RUNTIME` as the default behavior.
```kotlin theme={"dark"}
// Implicitly retains AnnotationRetention.RUNTIME
annotation class DefaultRetentionAnnotation
```
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