diff --git a/src/dotty/annotation/internal/Alias.scala b/src/dotty/annotation/internal/Alias.scala
index de51153f1ab4..8be83960f956 100644
--- a/src/dotty/annotation/internal/Alias.scala
+++ b/src/dotty/annotation/internal/Alias.scala
@@ -2,6 +2,9 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation to record a Scala2 pickled alias.
+ *  @param aliased  A TermRef pointing to the aliased field.
+ */
 class Alias(aliased: Any) extends Annotation {
 
 }
diff --git a/src/dotty/annotation/internal/AnnotationDefault.scala b/src/dotty/annotation/internal/AnnotationDefault.scala
index 90471b8fec38..7409b2f96b33 100644
--- a/src/dotty/annotation/internal/AnnotationDefault.scala
+++ b/src/dotty/annotation/internal/AnnotationDefault.scala
@@ -2,6 +2,7 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation to tag Java annotation default values */
 class AnnotationDefault extends Annotation {
 
 }
diff --git a/src/dotty/annotation/internal/Child.scala b/src/dotty/annotation/internal/Child.scala
index ac253ed8d07f..23ff2a97c00c 100644
--- a/src/dotty/annotation/internal/Child.scala
+++ b/src/dotty/annotation/internal/Child.scala
@@ -2,6 +2,5 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
-class Child[T] extends Annotation {
-
-}
+/** An annotation to indicate a child class or object of the annotated class. */
+class Child[T] extends Annotation
diff --git a/src/dotty/annotation/internal/Repeated.scala b/src/dotty/annotation/internal/Repeated.scala
index 3065b7a06567..24adc051fe27 100644
--- a/src/dotty/annotation/internal/Repeated.scala
+++ b/src/dotty/annotation/internal/Repeated.scala
@@ -2,4 +2,9 @@ package dotty.annotation.internal
 
 import scala.annotation.Annotation
 
+/** An annotation produced by desugaring to indicate that a
+ *  sequence is a repeated parameter. I.e.
+ *
+ *      T*  is expanded by Desugar to    Seq[T] @Repeated
+ */
 final class Repeated() extends Annotation