diff --git a/logstash-core/src/main/java/org/logstash/DLQEntry.java b/logstash-core/src/main/java/org/logstash/DLQEntry.java
index dd1aff303..26adaae8b 100644
--- a/logstash-core/src/main/java/org/logstash/DLQEntry.java
+++ b/logstash-core/src/main/java/org/logstash/DLQEntry.java
@@ -43,7 +43,9 @@ import java.io.IOException;
 import java.nio.ByteBuffer;
 import org.logstash.ackedqueue.Queueable;
 
-
+/**
+ * Dead letter queue item
+ */
 public class DLQEntry implements Cloneable, Queueable {
 
     private final Event event;
diff --git a/logstash-core/src/main/java/org/logstash/Event.java b/logstash-core/src/main/java/org/logstash/Event.java
index 8b037c55e..dc02e30b0 100644
--- a/logstash-core/src/main/java/org/logstash/Event.java
+++ b/logstash-core/src/main/java/org/logstash/Event.java
@@ -43,6 +43,9 @@ import java.util.Map;
 import static org.logstash.ObjectMappers.CBOR_MAPPER;
 import static org.logstash.ObjectMappers.JSON_MAPPER;
 
+/**
+ * Event implementation, is the Logstash's event implementation
+ * */
 public final class Event implements Cloneable, Queueable, co.elastic.logstash.api.Event {
 
     private boolean cancelled;
diff --git a/logstash-core/src/main/java/org/logstash/FieldReference.java b/logstash-core/src/main/java/org/logstash/FieldReference.java
index e7b58b074..768d4baea 100644
--- a/logstash-core/src/main/java/org/logstash/FieldReference.java
+++ b/logstash-core/src/main/java/org/logstash/FieldReference.java
@@ -29,6 +29,9 @@ import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import org.jruby.RubyString;
 
+/**
+ * Represents a reference to another field of the event {@link Event}
+ * */
 public final class FieldReference {
     /**
      * A custom unchecked {@link RuntimeException} that can be thrown by parsing methods when
diff --git a/logstash-core/src/main/java/org/logstash/RubyJavaIntegration.java b/logstash-core/src/main/java/org/logstash/RubyJavaIntegration.java
index 8a854af90..4ec9fadca 100644
--- a/logstash-core/src/main/java/org/logstash/RubyJavaIntegration.java
+++ b/logstash-core/src/main/java/org/logstash/RubyJavaIntegration.java
@@ -125,6 +125,9 @@ public final class RubyJavaIntegration {
         }
     }
 
+    /**
+     * Helper class to provide some typical Ruby methods to Java Collection class when used from Ruby
+     * */
     public static final class JavaCollectionOverride {
 
         private static final Collection<IRubyObject> NIL_COLLECTION =
@@ -223,6 +226,9 @@ public final class RubyJavaIntegration {
         }
     }
 
+    /**
+     * Helper class to provide "is_a?" method to Java Map class when use dfrom Ruby
+     * */
     public static final class JavaMapOverride {
 
         private JavaMapOverride() {
diff --git a/logstash-core/src/main/java/org/logstash/Util.java b/logstash-core/src/main/java/org/logstash/Util.java
index 325b93ce6..34a90530b 100644
--- a/logstash-core/src/main/java/org/logstash/Util.java
+++ b/logstash-core/src/main/java/org/logstash/Util.java
@@ -25,7 +25,9 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 
-
+/**
+ * Static utility methods that provide merge methods for List and Map.
+ */
 public class Util {
     private Util() {}
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/AckedBatch.java b/logstash-core/src/main/java/org/logstash/ackedqueue/AckedBatch.java
index cde1cab7e..da50414ec 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/AckedBatch.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/AckedBatch.java
@@ -28,6 +28,9 @@ import org.logstash.ext.JrubyEventExtLibrary.RubyEvent;
 
 import static org.logstash.RubyUtil.RUBY;
 
+/**
+ * Persistent queue batch of events collection
+ * */
 public final class AckedBatch {
     private Batch batch;
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/AckedReadBatch.java b/logstash-core/src/main/java/org/logstash/ackedqueue/AckedReadBatch.java
index cec53c340..fab490f20 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/AckedReadBatch.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/AckedReadBatch.java
@@ -31,6 +31,9 @@ import java.util.Collection;
 
 import static org.logstash.RubyUtil.RUBY;
 
+/**
+ * Persistent queue collection of events implementation
+ * */
 public final class AckedReadBatch implements QueueBatch {
 
     private AckedBatch ackedBatch;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Batch.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Batch.java
index 302a6ab55..9d08bb01a 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Batch.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Batch.java
@@ -26,6 +26,9 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+/**
+ * Container for a set of events from queue to be processed by filters/outputs.
+ * */
 public class Batch implements Closeable {
 
     private final List<Queueable> elements;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Checkpoint.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Checkpoint.java
index ad6bf764e..9c151cb18 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Checkpoint.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Checkpoint.java
@@ -20,6 +20,11 @@
 
 package org.logstash.ackedqueue;
 
+/**
+ * Persistent queue chekpoint. There is one checkpoint per queue, and simply it's a picture of some
+ * management data like first not acked sequence number.
+ *
+ * */
 public class Checkpoint {
 //    Checkpoint file structure see FileCheckpointIO
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Page.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Page.java
index a64c525be..7a18fe140 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Page.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Page.java
@@ -28,6 +28,10 @@ import org.codehaus.commons.nullanalysis.NotNull;
 import org.logstash.ackedqueue.io.CheckpointIO;
 import org.logstash.ackedqueue.io.PageIO;
 
+/**
+ * Represents persistent queue Page metadata, like the page number, the minimum sequence number contained in the page,
+ * the status of the page (writeable or not).
+ * */
 public final class Page implements Closeable {
     protected final int pageNum;
     protected long minSeqNum; // TODO: see if we can make it final?
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/PqCheck.java b/logstash-core/src/main/java/org/logstash/ackedqueue/PqCheck.java
index 0d02d258b..512ea6a81 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/PqCheck.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/PqCheck.java
@@ -30,6 +30,9 @@ import java.util.Comparator;
 import java.util.stream.StreamSupport;
 import org.logstash.ackedqueue.io.FileCheckpointIO;
 
+/**
+ * Utility application to detect corrupted persistent queues.
+ * */
 public final class PqCheck {
 
     private static final String DEFAULT_PQ_DIR = "data/queue/main";
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java
index 3c7232e15..12071554b 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Queue.java
@@ -46,6 +46,9 @@ import org.logstash.ackedqueue.io.MmapPageIOV2;
 import org.logstash.ackedqueue.io.PageIO;
 import org.logstash.common.FsUtil;
 
+/**
+ * Persistent queue implementation.
+ * */
 public final class Queue implements Closeable {
 
     private long seqNum;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueFactoryExt.java b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueFactoryExt.java
index dad620067..15b572d7d 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueFactoryExt.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueFactoryExt.java
@@ -36,6 +36,9 @@ import org.logstash.ackedqueue.ext.JRubyWrappedAckedQueueExt;
 import org.logstash.execution.AbstractWrappedQueueExt;
 import org.logstash.ext.JrubyWrappedSynchronousQueueExt;
 
+/**
+ * Persistent queue factory JRuby extension.
+ * */
 @JRubyClass(name = "QueueFactory")
 public final class QueueFactoryExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueRuntimeException.java b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueRuntimeException.java
index 70098bd3c..d40fb3d95 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueRuntimeException.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueRuntimeException.java
@@ -20,6 +20,9 @@
 
 package org.logstash.ackedqueue;
 
+/**
+ * Runtime exception specialization for persistent queue related runtime errors.
+ * */
 public class QueueRuntimeException extends RuntimeException {
 
     private static final long serialVersionUID = 1L;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueUpgrade.java b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueUpgrade.java
index 8147c092f..140120e55 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/QueueUpgrade.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/QueueUpgrade.java
@@ -41,6 +41,9 @@ import org.logstash.ackedqueue.io.MmapPageIOV1;
 import org.logstash.ackedqueue.io.MmapPageIOV2;
 import org.logstash.ackedqueue.io.PageIO;
 
+/**
+ * Exposes the {@link #upgradeQueueDirectoryToV2} method upgrade old v1 queue disk format to the new v2
+ * */
 public final class QueueUpgrade {
 
     private static final Logger LOGGER = LogManager.getLogger(QueueUpgrade.class);
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Queueable.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Queueable.java
index e4896e9b7..7cb203d25 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Queueable.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Queueable.java
@@ -22,6 +22,9 @@ package org.logstash.ackedqueue;
 
 import java.io.IOException;
 
+/**
+ * Subclasses that are stored in queues must implement this to provide serializer and deserializer.
+ * */
 public interface Queueable {
 
     byte[] serialize() throws IOException;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/SequencedList.java b/logstash-core/src/main/java/org/logstash/ackedqueue/SequencedList.java
index 1b07afa9f..4a26a47e6 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/SequencedList.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/SequencedList.java
@@ -23,6 +23,9 @@ package org.logstash.ackedqueue;
 import java.util.List;
 import org.logstash.ackedqueue.io.LongVector;
 
+/**
+ * Carries sequence numbers and items read from queue.
+ * */
 public class SequencedList<E> {
     private final List<E> elements;
     private final LongVector seqNums;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/Settings.java b/logstash-core/src/main/java/org/logstash/ackedqueue/Settings.java
index 3444a05b0..45b34fe0f 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/Settings.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/Settings.java
@@ -20,6 +20,9 @@
 
 package org.logstash.ackedqueue;
 
+/**
+ * Persistent queue settings definition.
+ * */
 public interface Settings {
 
     Class<? extends Queueable> getElementClass();
@@ -38,6 +41,9 @@ public interface Settings {
 
     boolean getCheckpointRetry();
 
+    /**
+     * Persistent queue Setting's fluent builder definition
+     * */
     interface Builder {
 
         Builder elementClass(Class<? extends Queueable> elementClass);
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/SettingsImpl.java b/logstash-core/src/main/java/org/logstash/ackedqueue/SettingsImpl.java
index b1e1e6c6d..417bc81a8 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/SettingsImpl.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/SettingsImpl.java
@@ -20,6 +20,9 @@
 
 package org.logstash.ackedqueue;
 
+/**
+ * Persistent queue settings implementation.
+ * */
 public class SettingsImpl implements Settings {
     private String dirForFiles;
     private Class<? extends Queueable> elementClass;
@@ -94,6 +97,9 @@ public class SettingsImpl implements Settings {
         return this.checkpointRetry;
     }
 
+    /**
+     * Default implementation for Setting's Builder
+     * */
     private static final class BuilderImpl implements Builder {
 
         /**
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyAckedQueueExt.java b/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyAckedQueueExt.java
index c7d1257e4..c320c116b 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyAckedQueueExt.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyAckedQueueExt.java
@@ -38,6 +38,9 @@ import org.logstash.ackedqueue.Batch;
 import org.logstash.ackedqueue.Queue;
 import org.logstash.ackedqueue.SettingsImpl;
 
+/**
+ * JRuby extension to wrap a persistent queue istance.
+ * */
 @JRubyClass(name = "AckedQueue")
 public final class JRubyAckedQueueExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyWrappedAckedQueueExt.java b/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyWrappedAckedQueueExt.java
index 6bc03d1fe..bfa077b70 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyWrappedAckedQueueExt.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/ext/JRubyWrappedAckedQueueExt.java
@@ -39,6 +39,9 @@ import org.logstash.ext.JrubyAckedReadClientExt;
 import org.logstash.ext.JrubyAckedWriteClientExt;
 import org.logstash.ext.JrubyEventExtLibrary;
 
+/**
+ * JRuby extension
+ * */
 @JRubyClass(name = "WrappedAckedQueue")
 public final class JRubyWrappedAckedQueueExt extends AbstractWrappedQueueExt {
 
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/io/CheckpointIO.java b/logstash-core/src/main/java/org/logstash/ackedqueue/io/CheckpointIO.java
index a8e3153c0..447ef7baa 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/io/CheckpointIO.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/io/CheckpointIO.java
@@ -23,6 +23,9 @@ package org.logstash.ackedqueue.io;
 import org.logstash.ackedqueue.Checkpoint;
 import java.io.IOException;
 
+/**
+ * Internal API to access checkpoint stored in files.
+ * */
 public interface CheckpointIO {
 
     // @return Checkpoint the written checkpoint object
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/io/FileCheckpointIO.java b/logstash-core/src/main/java/org/logstash/ackedqueue/io/FileCheckpointIO.java
index db40f65d0..4e0f8866d 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/io/FileCheckpointIO.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/io/FileCheckpointIO.java
@@ -33,6 +33,10 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.logstash.ackedqueue.Checkpoint;
 
+
+/**
+ * File implementation for {@link CheckpointIO}
+ * */
 public class FileCheckpointIO implements CheckpointIO {
 //    Checkpoint file structure
 //
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/io/LongVector.java b/logstash-core/src/main/java/org/logstash/ackedqueue/io/LongVector.java
index 18b312179..05343a8a5 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/io/LongVector.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/io/LongVector.java
@@ -20,6 +20,12 @@
 
 package org.logstash.ackedqueue.io;
 
+/**
+ * Internal class used in persistent queue implementation.
+ *
+ * It'a vector that stores primitives long (no autoboxing) expanding, by copy, the underling array when
+ * more space is needed.
+ * */
 public final class LongVector {
 
     private int count;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/io/MmapPageIOV2.java b/logstash-core/src/main/java/org/logstash/ackedqueue/io/MmapPageIOV2.java
index ecb4ee170..0de29a41c 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/io/MmapPageIOV2.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/io/MmapPageIOV2.java
@@ -35,6 +35,9 @@ import org.apache.logging.log4j.Logger;
 import org.logstash.LogstashJavaCompat;
 import org.logstash.ackedqueue.SequencedList;
 
+/**
+ * Internal API, v2 mmap implementation of {@link PageIO}
+ * */
 public final class MmapPageIOV2 implements PageIO {
 
     public static final byte VERSION_TWO = (byte) 2;
@@ -392,6 +395,9 @@ public final class MmapPageIOV2 implements PageIO {
         }
     }
 
+    /**
+     * Invalid Page structure exception
+     * */
     public static final class PageIOInvalidElementException extends IOException {
 
         private static final long serialVersionUID = 1L;
@@ -401,6 +407,9 @@ public final class MmapPageIOV2 implements PageIO {
         }
     }
 
+    /**
+     * Invalid page version exception.
+     * */
     public static final class PageIOInvalidVersionException extends IOException {
 
         private static final long serialVersionUID = 1L;
diff --git a/logstash-core/src/main/java/org/logstash/ackedqueue/io/PageIO.java b/logstash-core/src/main/java/org/logstash/ackedqueue/io/PageIO.java
index bee69a31a..98231e36e 100644
--- a/logstash-core/src/main/java/org/logstash/ackedqueue/io/PageIO.java
+++ b/logstash-core/src/main/java/org/logstash/ackedqueue/io/PageIO.java
@@ -25,6 +25,9 @@ import org.logstash.ackedqueue.SequencedList;
 import java.io.Closeable;
 import java.io.IOException;
 
+/**
+ * Internal API to access pages stored in files.
+ * */
 public interface PageIO extends Closeable {
 
     // the concrete class should be constructed with the pageNum, capacity and dirPath attributes
diff --git a/logstash-core/src/main/java/org/logstash/execution/AbstractPipelineExt.java b/logstash-core/src/main/java/org/logstash/execution/AbstractPipelineExt.java
index b36936ac7..d08385be8 100644
--- a/logstash-core/src/main/java/org/logstash/execution/AbstractPipelineExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/AbstractPipelineExt.java
@@ -65,6 +65,9 @@ import org.logstash.instrument.metrics.NullMetricExt;
 import org.logstash.secret.store.SecretStore;
 import org.logstash.secret.store.SecretStoreExt;
 
+/**
+ * JRuby extension to provide ancestor class for Ruby's Pipeline and JavaPipeline classes.
+ * */
 @JRubyClass(name = "AbstractPipeline")
 public class AbstractPipelineExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/AbstractWrappedQueueExt.java b/logstash-core/src/main/java/org/logstash/execution/AbstractWrappedQueueExt.java
index 0a16fb896..128cc00fa 100644
--- a/logstash-core/src/main/java/org/logstash/execution/AbstractWrappedQueueExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/AbstractWrappedQueueExt.java
@@ -29,6 +29,9 @@ import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 import org.logstash.ext.JRubyAbstractQueueWriteClientExt;
 
+/**
+ * Interface definition for JRuby extensions for in memory and persistent queue
+ * */
 @JRubyClass(name = "AbstractWrappedQueue")
 public abstract class AbstractWrappedQueueExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/ConvergeResultExt.java b/logstash-core/src/main/java/org/logstash/execution/ConvergeResultExt.java
index 4d912a0f3..14a71de8a 100644
--- a/logstash-core/src/main/java/org/logstash/execution/ConvergeResultExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/ConvergeResultExt.java
@@ -33,6 +33,9 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
+/**
+ * JRuby extension, used by agent to collect the results of running pipeliene actions (Create, Update, Delete)
+ * */
 @JRubyClass(name = "ConvergeResult")
 public class ConvergeResultExt extends RubyObject {
 
@@ -102,6 +105,9 @@ public class ConvergeResultExt extends RubyObject {
     }
 
 
+    /**
+     * Base class for all action results classes (Failed / Success)
+     * */
     @JRubyClass(name = "ActionResult")
     public static abstract class ActionResultExt extends RubyBasicObject {
 
@@ -153,6 +159,9 @@ public class ConvergeResultExt extends RubyObject {
         protected abstract boolean getSuccessFul();
     }
 
+    /**
+     * Failed result of running an action.
+     * */
     @JRubyClass(name = "FailedAction")
     public static final class FailedActionExt extends ActionResultExt {
 
@@ -209,6 +218,9 @@ public class ConvergeResultExt extends RubyObject {
         }
     }
 
+    /**
+     * Successful result of running an action.
+     * */
     @JRubyClass(name = "SuccessfulAction")
     public static final class SuccessfulActionExt extends ActionResultExt {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/EventDispatcherExt.java b/logstash-core/src/main/java/org/logstash/execution/EventDispatcherExt.java
index 507015e87..792f29632 100644
--- a/logstash-core/src/main/java/org/logstash/execution/EventDispatcherExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/EventDispatcherExt.java
@@ -30,6 +30,9 @@ import org.jruby.anno.JRubyMethod;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 
+/**
+ * JRuby extension that provides a class to keep track of listener and dispatch events to those.
+ * */
 @JRubyClass(name = "EventDispatcher")
 public final class EventDispatcherExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/ExecutionContextExt.java b/logstash-core/src/main/java/org/logstash/execution/ExecutionContextExt.java
index f7815c746..cdd212571 100644
--- a/logstash-core/src/main/java/org/logstash/execution/ExecutionContextExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/ExecutionContextExt.java
@@ -31,6 +31,10 @@ import org.jruby.runtime.builtin.IRubyObject;
 import org.logstash.RubyUtil;
 import org.logstash.common.AbstractDeadLetterQueueWriterExt;
 
+/**
+ * JRuby extension to provide execution context to the plugins,
+ * instantiated by {@link org.logstash.plugins.factory.ExecutionContextFactoryExt}
+ * */
 @JRubyClass(name = "ExecutionContext")
 public final class ExecutionContextExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/JavaBasePipelineExt.java b/logstash-core/src/main/java/org/logstash/execution/JavaBasePipelineExt.java
index 7d58f2c1a..4367652aa 100644
--- a/logstash-core/src/main/java/org/logstash/execution/JavaBasePipelineExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/JavaBasePipelineExt.java
@@ -44,6 +44,9 @@ import java.security.NoSuchAlgorithmException;
 import java.util.Collection;
 import java.util.stream.Stream;
 
+/**
+ * JRuby extension used as parent for Ruby's JavaPipelines
+ * */
 @JRubyClass(name = "JavaBasePipeline")
 public final class JavaBasePipelineExt extends AbstractPipelineExt {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/MemoryReadBatch.java b/logstash-core/src/main/java/org/logstash/execution/MemoryReadBatch.java
index 5108d0a3d..6a70db2cb 100644
--- a/logstash-core/src/main/java/org/logstash/execution/MemoryReadBatch.java
+++ b/logstash-core/src/main/java/org/logstash/execution/MemoryReadBatch.java
@@ -26,6 +26,9 @@ import java.util.Collection;
 
 import static org.logstash.RubyUtil.RUBY;
 
+/**
+ * In memory queue collection of events implementation
+ * */
 public final class MemoryReadBatch implements QueueBatch {
 
     private final Collection<RubyEvent> events;
diff --git a/logstash-core/src/main/java/org/logstash/execution/PeriodicFlush.java b/logstash-core/src/main/java/org/logstash/execution/PeriodicFlush.java
index 329f51013..2d506652f 100644
--- a/logstash-core/src/main/java/org/logstash/execution/PeriodicFlush.java
+++ b/logstash-core/src/main/java/org/logstash/execution/PeriodicFlush.java
@@ -28,6 +28,9 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
 @SuppressWarnings("try")
+/**
+ * Used by Ruby's JavaPipeline
+ * */
 public final class PeriodicFlush implements AutoCloseable {
 
     private static final Logger LOGGER = LogManager.getLogger(PeriodicFlush.class);
diff --git a/logstash-core/src/main/java/org/logstash/execution/PipelineReporterExt.java b/logstash-core/src/main/java/org/logstash/execution/PipelineReporterExt.java
index 46e4f6720..1d59f8cdc 100644
--- a/logstash-core/src/main/java/org/logstash/execution/PipelineReporterExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/PipelineReporterExt.java
@@ -37,6 +37,9 @@ import org.logstash.config.ir.compiler.AbstractOutputDelegatorExt;
 
 import java.util.Collection;
 
+/**
+ * JRuby extension
+ * */
 @JRubyClass(name = "PipelineReporter")
 public final class PipelineReporterExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/QueueBatch.java b/logstash-core/src/main/java/org/logstash/execution/QueueBatch.java
index 7da54d6f5..f7b9d59ea 100644
--- a/logstash-core/src/main/java/org/logstash/execution/QueueBatch.java
+++ b/logstash-core/src/main/java/org/logstash/execution/QueueBatch.java
@@ -24,6 +24,9 @@ import org.logstash.ext.JrubyEventExtLibrary.RubyEvent;
 import java.io.IOException;
 import java.util.Collection;
 
+/**
+ * Defines collection of queue events to be processed.
+ * */
 public interface QueueBatch {
     int filteredSize();
     RubyArray<RubyEvent> to_a();
diff --git a/logstash-core/src/main/java/org/logstash/execution/QueueReadClient.java b/logstash-core/src/main/java/org/logstash/execution/QueueReadClient.java
index ac78034eb..ccca34a39 100644
--- a/logstash-core/src/main/java/org/logstash/execution/QueueReadClient.java
+++ b/logstash-core/src/main/java/org/logstash/execution/QueueReadClient.java
@@ -22,6 +22,9 @@ package org.logstash.execution;
 
 import java.io.IOException;
 
+/**
+ * Defines the methods to interact with queues from the the reader perspective
+ * */
 public interface QueueReadClient {
     QueueBatch readBatch() throws InterruptedException;
     QueueBatch newBatch();
diff --git a/logstash-core/src/main/java/org/logstash/execution/QueueReadClientBase.java b/logstash-core/src/main/java/org/logstash/execution/QueueReadClientBase.java
index d4eb6a05f..dd8408a32 100644
--- a/logstash-core/src/main/java/org/logstash/execution/QueueReadClientBase.java
+++ b/logstash-core/src/main/java/org/logstash/execution/QueueReadClientBase.java
@@ -39,6 +39,9 @@ import java.io.IOException;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 
+/**
+ * Common code shared by Persistent and In-Memory queues clients implementation
+ * */
 @JRubyClass(name = "QueueReadClientBase")
 public abstract class QueueReadClientBase extends RubyObject implements QueueReadClient {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/ShutdownWatcherExt.java b/logstash-core/src/main/java/org/logstash/execution/ShutdownWatcherExt.java
index 12930b51a..3ac84ec4f 100644
--- a/logstash-core/src/main/java/org/logstash/execution/ShutdownWatcherExt.java
+++ b/logstash-core/src/main/java/org/logstash/execution/ShutdownWatcherExt.java
@@ -37,6 +37,9 @@ import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 import org.logstash.RubyUtil;
 
+/**
+ * JRuby extension, used by pipelines to execute the shutdown flow of a pipeline.
+ * */
 @JRubyClass(name = "ShutdownWatcher")
 public final class ShutdownWatcherExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/execution/WorkerLoop.java b/logstash-core/src/main/java/org/logstash/execution/WorkerLoop.java
index b0e974d3d..3a0c97ddb 100644
--- a/logstash-core/src/main/java/org/logstash/execution/WorkerLoop.java
+++ b/logstash-core/src/main/java/org/logstash/execution/WorkerLoop.java
@@ -25,6 +25,10 @@ import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.logstash.config.ir.CompiledPipeline;
 
+/**
+ * Pipeline execution worker, it's responsible to execute filters and output plugins for each {@link QueueBatch} that
+ * pull out from queue.
+ * */
 public final class WorkerLoop implements Runnable {
 
     private static final Logger LOGGER = LogManager.getLogger(WorkerLoop.class);
diff --git a/logstash-core/src/main/java/org/logstash/execution/queue/LegacyMemoryQueueWriter.java b/logstash-core/src/main/java/org/logstash/execution/queue/LegacyMemoryQueueWriter.java
deleted file mode 100644
index 15f3a7b1e..000000000
--- a/logstash-core/src/main/java/org/logstash/execution/queue/LegacyMemoryQueueWriter.java
+++ /dev/null
@@ -1,46 +0,0 @@
-/*
- * Licensed to Elasticsearch B.V. under one or more contributor
- * license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright
- * ownership. Elasticsearch B.V. licenses this file to you under
- * the Apache License, Version 2.0 (the "License"); you may
- * not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *	http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-
-package org.logstash.execution.queue;
-
-import java.util.Map;
-import java.util.concurrent.BlockingQueue;
-import org.logstash.Event;
-import org.logstash.RubyUtil;
-import org.logstash.ext.JrubyEventExtLibrary;
-
-public final class LegacyMemoryQueueWriter implements QueueWriter {
-
-    private final BlockingQueue<JrubyEventExtLibrary.RubyEvent> queue;
-
-    public LegacyMemoryQueueWriter(final BlockingQueue<JrubyEventExtLibrary.RubyEvent> queue) {
-        this.queue = queue;
-    }
-
-    @Override
-    public void push(final Map<String, Object> event) {
-        try {
-            queue.put(JrubyEventExtLibrary.RubyEvent.newRubyEvent(RubyUtil.RUBY, new Event(event)));
-        } catch (final InterruptedException ex) {
-            throw new IllegalStateException(ex);
-        }
-    }
-
-}
diff --git a/logstash-core/src/main/java/org/logstash/ext/JrubyAckedReadClientExt.java b/logstash-core/src/main/java/org/logstash/ext/JrubyAckedReadClientExt.java
index 3807ed688..273fa6cb2 100644
--- a/logstash-core/src/main/java/org/logstash/ext/JrubyAckedReadClientExt.java
+++ b/logstash-core/src/main/java/org/logstash/ext/JrubyAckedReadClientExt.java
@@ -35,6 +35,9 @@ import org.logstash.execution.QueueReadClientBase;
 
 import java.io.IOException;
 
+/**
+ * JRuby extension to provide an implementation of queue client for Persistent queue
+ * */
 @JRubyClass(name = "AckedReadClient", parent = "QueueReadClientBase")
 public final class JrubyAckedReadClientExt extends QueueReadClientBase implements QueueReadClient {
 
diff --git a/logstash-core/src/main/java/org/logstash/ext/JrubyMemoryReadClientExt.java b/logstash-core/src/main/java/org/logstash/ext/JrubyMemoryReadClientExt.java
index 95e173b6a..f8da9c367 100644
--- a/logstash-core/src/main/java/org/logstash/ext/JrubyMemoryReadClientExt.java
+++ b/logstash-core/src/main/java/org/logstash/ext/JrubyMemoryReadClientExt.java
@@ -31,6 +31,9 @@ import org.logstash.execution.MemoryReadBatch;
 import org.logstash.execution.QueueBatch;
 import org.logstash.execution.QueueReadClientBase;
 
+/**
+ * JRuby extension to provide an implementation of queue client for InMemory queue
+ * */
 @JRubyClass(name = "MemoryReadClient", parent = "QueueReadClientBase")
 public final class JrubyMemoryReadClientExt extends QueueReadClientBase {
 
diff --git a/logstash-core/src/main/java/org/logstash/ext/JrubyWrappedSynchronousQueueExt.java b/logstash-core/src/main/java/org/logstash/ext/JrubyWrappedSynchronousQueueExt.java
index 4962dffc6..c75156280 100644
--- a/logstash-core/src/main/java/org/logstash/ext/JrubyWrappedSynchronousQueueExt.java
+++ b/logstash-core/src/main/java/org/logstash/ext/JrubyWrappedSynchronousQueueExt.java
@@ -32,6 +32,9 @@ import org.jruby.runtime.builtin.IRubyObject;
 import org.logstash.execution.AbstractWrappedQueueExt;
 import org.logstash.execution.QueueReadClientBase;
 
+/**
+ * JRuby extension to wrap in memory queue
+ * */
 @JRubyClass(name = "WrappedSynchronousQueue")
 public final class JrubyWrappedSynchronousQueueExt extends AbstractWrappedQueueExt {
 
diff --git a/logstash-core/src/main/java/org/logstash/instrument/metrics/AbstractMetricExt.java b/logstash-core/src/main/java/org/logstash/instrument/metrics/AbstractMetricExt.java
index ed4650a84..38ed25ad7 100644
--- a/logstash-core/src/main/java/org/logstash/instrument/metrics/AbstractMetricExt.java
+++ b/logstash-core/src/main/java/org/logstash/instrument/metrics/AbstractMetricExt.java
@@ -28,6 +28,9 @@ import org.jruby.anno.JRubyMethod;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 
+/**
+ * JRuby extension to model the metrics collection
+ * */
 @JRubyClass(name = "AbstractMetric")
 public abstract class AbstractMetricExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/CustomLogEvent.java b/logstash-core/src/main/java/org/logstash/log/CustomLogEvent.java
index bc6d0b10f..6de6a9671 100644
--- a/logstash-core/src/main/java/org/logstash/log/CustomLogEvent.java
+++ b/logstash-core/src/main/java/org/logstash/log/CustomLogEvent.java
@@ -48,6 +48,9 @@ import org.apache.logging.log4j.message.Message;
 
 import java.util.List;
 
+/**
+ * Customized Logstash log event
+ * */
 @JsonSerialize(using = CustomLogEventSerializer.class)
 public class CustomLogEvent extends Log4jLogEvent {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/CustomLogEventSerializer.java b/logstash-core/src/main/java/org/logstash/log/CustomLogEventSerializer.java
index a31d3c753..cfda88a3e 100644
--- a/logstash-core/src/main/java/org/logstash/log/CustomLogEventSerializer.java
+++ b/logstash-core/src/main/java/org/logstash/log/CustomLogEventSerializer.java
@@ -28,6 +28,9 @@ import com.fasterxml.jackson.databind.SerializerProvider;
 import java.io.IOException;
 import java.util.Map;
 
+/**
+ * Json serializer for logging messages, use in json appender.
+ * */
 public class CustomLogEventSerializer extends JsonSerializer<CustomLogEvent> {
     @Override
     public void serialize(CustomLogEvent event, JsonGenerator generator, SerializerProvider provider) throws IOException {
diff --git a/logstash-core/src/main/java/org/logstash/log/DeprecationLoggerExt.java b/logstash-core/src/main/java/org/logstash/log/DeprecationLoggerExt.java
index f4a926412..8dd2e1e2f 100644
--- a/logstash-core/src/main/java/org/logstash/log/DeprecationLoggerExt.java
+++ b/logstash-core/src/main/java/org/logstash/log/DeprecationLoggerExt.java
@@ -29,6 +29,9 @@ import org.jruby.anno.JRubyMethod;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 
+/**
+ * JRuby extension to provide deprecation logger functionality to Ruby classes
+ * */
 @JRubyClass(name = "DeprecationLogger")
 public class DeprecationLoggerExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/LoggableExt.java b/logstash-core/src/main/java/org/logstash/log/LoggableExt.java
index a85dd7239..caef20eaf 100644
--- a/logstash-core/src/main/java/org/logstash/log/LoggableExt.java
+++ b/logstash-core/src/main/java/org/logstash/log/LoggableExt.java
@@ -33,6 +33,9 @@ import java.util.Locale;
 
 import static org.logstash.log.SlowLoggerExt.toLong;
 
+/**
+ * JRuby extension, it's part of log4j wrapping for JRuby.
+ * */
 @JRubyModule(name = "Loggable")
 public final class LoggableExt {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/LoggerExt.java b/logstash-core/src/main/java/org/logstash/log/LoggerExt.java
index 946416b23..dae0f97de 100644
--- a/logstash-core/src/main/java/org/logstash/log/LoggerExt.java
+++ b/logstash-core/src/main/java/org/logstash/log/LoggerExt.java
@@ -39,6 +39,10 @@ import org.jruby.runtime.builtin.IRubyObject;
 import java.io.File;
 import java.net.URI;
 
+/**
+ * JRuby extension, it's part of log4j wrapping for JRuby.
+ * Wrapper log4j Logger as Ruby like class
+ * */
 @JRubyClass(name = "Logger")
 public class LoggerExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/LogstashConfigurationFactory.java b/logstash-core/src/main/java/org/logstash/log/LogstashConfigurationFactory.java
index 5fc50e328..ee1eb3f35 100644
--- a/logstash-core/src/main/java/org/logstash/log/LogstashConfigurationFactory.java
+++ b/logstash-core/src/main/java/org/logstash/log/LogstashConfigurationFactory.java
@@ -33,6 +33,10 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.Properties;
 
+/**
+ * Logstash configuration factory customization used to remove the routing appender from log4j configuration
+ * if "separate_logs" settings is false.
+ * */
 @Plugin(name = "LogstashConfigurationFactory", category = ConfigurationFactory.CATEGORY)
 @Order(9)
 public class LogstashConfigurationFactory extends ConfigurationFactory {
diff --git a/logstash-core/src/main/java/org/logstash/log/LogstashLogEventFactory.java b/logstash-core/src/main/java/org/logstash/log/LogstashLogEventFactory.java
index 6b253c9f9..4ecf21ab1 100644
--- a/logstash-core/src/main/java/org/logstash/log/LogstashLogEventFactory.java
+++ b/logstash-core/src/main/java/org/logstash/log/LogstashLogEventFactory.java
@@ -29,6 +29,9 @@ import org.apache.logging.log4j.message.Message;
 
 import java.util.List;
 
+/**
+ * Logstash implementation of factory for Log4j LogEvent
+ * */
 public class LogstashLogEventFactory implements LogEventFactory {
     @Override
     public LogEvent createEvent(String loggerName, Marker marker, String fqcn, Level level, Message data, List<Property> properties, Throwable t) {
diff --git a/logstash-core/src/main/java/org/logstash/log/LogstashMessageFactory.java b/logstash-core/src/main/java/org/logstash/log/LogstashMessageFactory.java
index 609de6b4a..cca2f1418 100644
--- a/logstash-core/src/main/java/org/logstash/log/LogstashMessageFactory.java
+++ b/logstash-core/src/main/java/org/logstash/log/LogstashMessageFactory.java
@@ -28,6 +28,9 @@ import org.apache.logging.log4j.message.SimpleMessage;
 
 import java.util.Map;
 
+/**
+ * Used in Log4j configuration.
+ * */
 public final class LogstashMessageFactory implements MessageFactory {
 
     public static final LogstashMessageFactory INSTANCE = new LogstashMessageFactory();
diff --git a/logstash-core/src/main/java/org/logstash/log/SlowLoggerExt.java b/logstash-core/src/main/java/org/logstash/log/SlowLoggerExt.java
index 21f63c730..741200a32 100644
--- a/logstash-core/src/main/java/org/logstash/log/SlowLoggerExt.java
+++ b/logstash-core/src/main/java/org/logstash/log/SlowLoggerExt.java
@@ -34,6 +34,9 @@ import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 import org.logstash.RubyUtil;
 
+/**
+ * JRuby extension to provide slow logger functionality to Ruby classes
+ * */
 @JRubyClass(name = "SlowLogger")
 public class SlowLoggerExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/log/StructuredMessage.java b/logstash-core/src/main/java/org/logstash/log/StructuredMessage.java
index 44b6d3895..810d71413 100644
--- a/logstash-core/src/main/java/org/logstash/log/StructuredMessage.java
+++ b/logstash-core/src/main/java/org/logstash/log/StructuredMessage.java
@@ -26,6 +26,9 @@ import org.apache.logging.log4j.message.Message;
 import java.util.HashMap;
 import java.util.Map;
 
+/**
+ * Logging message extension class
+ * */
 @JsonSerialize(using = CustomLogEventSerializer.class)
 public class StructuredMessage implements Message {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/ConfigVariableExpander.java b/logstash-core/src/main/java/org/logstash/plugins/ConfigVariableExpander.java
index fb1247f3c..a66037a07 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/ConfigVariableExpander.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/ConfigVariableExpander.java
@@ -28,6 +28,10 @@ import java.nio.charset.StandardCharsets;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
+/**
+ * Expand the configuration variables used in pipeline configuration, bringing them from secret store or from the
+ * environment.
+ * */
 public class ConfigVariableExpander implements AutoCloseable {
 
     private static String SUBSTITUTION_PLACEHOLDER_REGEX = "\\$\\{(?<name>[a-zA-Z_.][a-zA-Z0-9_.]*)(:(?<default>[^}]*))?}";
diff --git a/logstash-core/src/main/java/org/logstash/plugins/ContextImpl.java b/logstash-core/src/main/java/org/logstash/plugins/ContextImpl.java
index 0fcbdc032..5ee3e48cf 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/ContextImpl.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/ContextImpl.java
@@ -29,6 +29,9 @@ import org.logstash.log.DefaultDeprecationLogger;
 import java.io.Serializable;
 import java.util.Map;
 
+/**
+ * Default implementation of Logstash Plugin's {@link Context}
+ * */
 public class ContextImpl implements Context {
 
     private DeadLetterQueueWriter dlqWriter;
diff --git a/logstash-core/src/main/java/org/logstash/plugins/CounterMetricImpl.java b/logstash-core/src/main/java/org/logstash/plugins/CounterMetricImpl.java
index 87226ee17..be652d4df 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/CounterMetricImpl.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/CounterMetricImpl.java
@@ -25,6 +25,9 @@ import org.jruby.runtime.ThreadContext;
 import org.logstash.instrument.metrics.AbstractNamespacedMetricExt;
 import org.logstash.instrument.metrics.counter.LongCounter;
 
+/**
+ * Default implementation of {@link CounterMetric}
+ * */
 public class CounterMetricImpl implements CounterMetric {
     private LongCounter longCounter;
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/HooksRegistryExt.java b/logstash-core/src/main/java/org/logstash/plugins/HooksRegistryExt.java
index d2534ba06..516163e06 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/HooksRegistryExt.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/HooksRegistryExt.java
@@ -34,6 +34,9 @@ import java.util.List;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 
+/**
+ * JRuby extension class that collect all the emitters and hooks
+ * */
 @JRubyClass(name = "HooksRegistry")
 public final class HooksRegistryExt extends RubyObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/PluginLookup.java b/logstash-core/src/main/java/org/logstash/plugins/PluginLookup.java
index 2b09e49b0..c61bacc75 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/PluginLookup.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/PluginLookup.java
@@ -106,6 +106,9 @@ public final class PluginLookup {
         }
     }
 
+    /**
+     * Descriptor of a plugin implementation. Defines the implementation language and the plugin class
+     * */
     public interface PluginClass {
         PluginLookup.PluginLanguage language();
 
@@ -116,10 +119,16 @@ public final class PluginLookup {
         }
     }
 
+    /**
+     * Enum all the implementation languages used by plugins
+     * */
     public enum PluginLanguage {
         JAVA, RUBY
     }
 
+    /**
+     * Enum all the plugins types used inside Logstash
+     * */
     public enum PluginType {
         INPUT("input", "inputs", Input.class),
         FILTER("filter", "filters", Filter.class),
diff --git a/logstash-core/src/main/java/org/logstash/plugins/PluginUtil.java b/logstash-core/src/main/java/org/logstash/plugins/PluginUtil.java
index 7fa78650a..3a23e1814 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/PluginUtil.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/PluginUtil.java
@@ -33,6 +33,9 @@ import java.util.Collection;
 import java.util.List;
 import java.util.stream.Collectors;
 
+/**
+ * Plugin's utility methods
+ * */
 public class PluginUtil {
 
     private PluginUtil() { /* utility methods */ }
diff --git a/logstash-core/src/main/java/org/logstash/plugins/codecs/Dots.java b/logstash-core/src/main/java/org/logstash/plugins/codecs/Dots.java
index 3326161d0..acad62ff8 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/codecs/Dots.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/codecs/Dots.java
@@ -36,6 +36,9 @@ import java.util.Map;
 import java.util.UUID;
 import java.util.function.Consumer;
 
+/**
+ * Java implementation of the "dots" codec
+ * */
 @LogstashPlugin(name = "jdots")
 public class Dots implements Codec {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/codecs/Line.java b/logstash-core/src/main/java/org/logstash/plugins/codecs/Line.java
index e42c5fa9f..9e3570c50 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/codecs/Line.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/codecs/Line.java
@@ -46,6 +46,9 @@ import java.util.function.Consumer;
 
 import static org.logstash.ObjectMappers.JSON_MAPPER;
 
+/**
+ * Java implementation of the "line" codec
+ * */
 @LogstashPlugin(name = "java_line")
 public class Line implements Codec {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/factory/ExecutionContextFactoryExt.java b/logstash-core/src/main/java/org/logstash/plugins/factory/ExecutionContextFactoryExt.java
index 2799eb12c..aa822bedf 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/factory/ExecutionContextFactoryExt.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/factory/ExecutionContextFactoryExt.java
@@ -19,6 +19,9 @@ import org.logstash.plugins.ContextImpl;
 import org.logstash.plugins.NamespacedMetricImpl;
 import org.logstash.plugins.PluginLookup;
 
+/**
+ * JRuby extension, factory class for plugins execution contexts
+ * */
 @JRubyClass(name = "ExecutionContextFactory")
 public final class ExecutionContextFactoryExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/factory/PluginFactoryExt.java b/logstash-core/src/main/java/org/logstash/plugins/factory/PluginFactoryExt.java
index 0d3226e07..6365d63aa 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/factory/PluginFactoryExt.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/factory/PluginFactoryExt.java
@@ -25,10 +25,16 @@ import org.logstash.plugins.PluginLookup;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 
+/**
+ * JRuby extension to implement the factory that create plugin instances
+ * */
 @JRubyClass(name = "PluginFactory")
 public final class PluginFactoryExt extends RubyBasicObject
     implements RubyIntegration.PluginFactory {
 
+    /**
+     * Definition of plugin resolver, maps plugin type and name to the plugin's class.
+     * */
     @FunctionalInterface
     public interface PluginResolver {
         PluginLookup.PluginClass resolve(PluginLookup.PluginType type, String name);
diff --git a/logstash-core/src/main/java/org/logstash/plugins/factory/PluginMetricsFactoryExt.java b/logstash-core/src/main/java/org/logstash/plugins/factory/PluginMetricsFactoryExt.java
index 18a8aab33..339ee7f3f 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/factory/PluginMetricsFactoryExt.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/factory/PluginMetricsFactoryExt.java
@@ -13,6 +13,9 @@ import org.logstash.instrument.metrics.NullMetricExt;
 
 import java.util.Arrays;
 
+/**
+ * JRuby extension to implement a factory class for Plugin's metrics
+ * */
 @JRubyClass(name = "PluginMetricsFactory")
 public final class PluginMetricsFactoryExt extends RubyBasicObject {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/filters/Uuid.java b/logstash-core/src/main/java/org/logstash/plugins/filters/Uuid.java
index 05e72823e..db3b79c7c 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/filters/Uuid.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/filters/Uuid.java
@@ -33,6 +33,9 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.UUID;
 
+/**
+ * Java implementation of the "uuid" filter
+ * */
 @LogstashPlugin(name = "java_uuid")
 public class Uuid implements Filter {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/inputs/Generator.java b/logstash-core/src/main/java/org/logstash/plugins/inputs/Generator.java
index bd1949c8e..ab58663e8 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/inputs/Generator.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/inputs/Generator.java
@@ -42,6 +42,9 @@ import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 
+/**
+ * Java implementation of the "generator" input
+ * */
 @LogstashPlugin(name = "java_generator")
 public class Generator implements Input {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/inputs/Stdin.java b/logstash-core/src/main/java/org/logstash/plugins/inputs/Stdin.java
index 6fd455156..5b2808a19 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/inputs/Stdin.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/inputs/Stdin.java
@@ -43,6 +43,9 @@ import java.util.Map;
 import java.util.concurrent.CountDownLatch;
 import java.util.function.Consumer;
 
+/**
+ * Java implementation of the "stdin" input
+ * */
 @LogstashPlugin(name = "java_stdin")
 public class Stdin implements Input, Consumer<Map<String, Object>> {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/outputs/Sink.java b/logstash-core/src/main/java/org/logstash/plugins/outputs/Sink.java
index 3a756abac..3caf37d18 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/outputs/Sink.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/outputs/Sink.java
@@ -30,6 +30,9 @@ import co.elastic.logstash.api.PluginHelper;
 
 import java.util.Collection;
 
+/**
+ * Java implementation of "sink" output plugin
+ * */
 @LogstashPlugin(name = "sink")
 public class Sink implements Output {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/outputs/Stdout.java b/logstash-core/src/main/java/org/logstash/plugins/outputs/Stdout.java
index f112f138f..47124091e 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/outputs/Stdout.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/outputs/Stdout.java
@@ -35,6 +35,9 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.concurrent.CountDownLatch;
 
+/**
+ * Java implementation of the "stdout" output plugin
+ * */
 @LogstashPlugin(name = "java_stdout")
 public class Stdout implements Output {
 
diff --git a/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineInput.java b/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineInput.java
index f29a24faa..b3500a47a 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineInput.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineInput.java
@@ -24,6 +24,9 @@ import org.logstash.ext.JrubyEventExtLibrary;
 
 import java.util.stream.Stream;
 
+/**
+ * Represents the in endpoint of a pipeline to pipeline communication.
+ * */
 public interface PipelineInput {
     /**
      * Accepts an event. It might be rejected if the input is stopping.
diff --git a/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineOutput.java b/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineOutput.java
index a9247201c..47f6c77d1 100644
--- a/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineOutput.java
+++ b/logstash-core/src/main/java/org/logstash/plugins/pipeline/PipelineOutput.java
@@ -20,5 +20,8 @@
 
 package org.logstash.plugins.pipeline;
 
+/**
+ * Represents the out endpoint of a pipeline to pipeline communication.
+ * */
 public interface PipelineOutput {
 }
diff --git a/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreException.java b/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreException.java
index ac1b3dc2c..33bb02654 100644
--- a/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreException.java
+++ b/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreException.java
@@ -37,6 +37,9 @@ public class SecretStoreException extends RuntimeException {
         super(message);
     }
 
+    /**
+     * Error in retrive a secret from a keystore
+     * */
     static public class RetrievalException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public RetrievalException(SecretIdentifier secretIdentifier, Throwable cause) {
@@ -44,6 +47,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Error in listing secrets in key store
+     * */
     static public class ListException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public ListException(Throwable cause) {
@@ -51,6 +57,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Error in creating Logstash key store
+     * */
     static public class CreateException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public CreateException(String message, Throwable cause) {
@@ -62,6 +71,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Error in loading a key store, probably because it's not a Logstash keystore
+     * */
     static public class LoadException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public LoadException(String message, Throwable cause) {
@@ -73,6 +85,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Error in persisting a secret into a keystore
+     * */
     static public class PersistException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public PersistException(SecretIdentifier secretIdentifier, Throwable cause) {
@@ -80,6 +95,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Error in purge a secret from a keystore
+     * */
     static public class PurgeException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public PurgeException(SecretIdentifier secretIdentifier, Throwable cause) {
@@ -87,6 +105,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Generic error
+     * */
     static public class UnknownException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public UnknownException(String message, Throwable cause) {
@@ -94,6 +115,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Problem with "keystore.classname", can't be instantiated or class can't be found
+     * */
     static public class ImplementationNotFoundException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public ImplementationNotFoundException(String message, Throwable throwable) {
@@ -101,6 +125,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Problem with the value of "keystore.classname", class is invalid or not accessible
+     * */
     static public class ImplementationInvalidException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public ImplementationInvalidException(String message, Throwable throwable) {
@@ -108,6 +135,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Launched when there is problem accessing a keystore, for example the user provided empty password
+     * */
     static public class AccessException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public AccessException(String message, Throwable throwable) {
@@ -119,6 +149,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Launched when a keystore already exists
+     * */
     static public class AlreadyExistsException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public AlreadyExistsException(String message) {
@@ -126,6 +159,9 @@ public class SecretStoreException extends RuntimeException {
         }
     }
 
+    /**
+     * Never used
+     * */
     static public class InvalidConfigurationException extends SecretStoreException {
         private static final long serialVersionUID = 1L;
         public InvalidConfigurationException(String message) {
diff --git a/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreExt.java b/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreExt.java
index 1fa782f42..b1f1a2ba2 100644
--- a/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreExt.java
+++ b/logstash-core/src/main/java/org/logstash/secret/store/SecretStoreExt.java
@@ -24,6 +24,9 @@ import org.jruby.RubyHash;
 import org.logstash.RubyUtil;
 import org.logstash.secret.SecretIdentifier;
 
+/**
+ * Collect static methods to access Java keystore
+ * */
 public class SecretStoreExt {
 
     private static final SecretStoreFactory SECRET_STORE_FACTORY = SecretStoreFactory.fromEnvironment();
diff --git a/logstash-core/src/main/java/org/logstash/util/CloudSettingAuth.java b/logstash-core/src/main/java/org/logstash/util/CloudSettingAuth.java
index 9d89e3e94..c251bf415 100644
--- a/logstash-core/src/main/java/org/logstash/util/CloudSettingAuth.java
+++ b/logstash-core/src/main/java/org/logstash/util/CloudSettingAuth.java
@@ -22,6 +22,9 @@ package org.logstash.util;
 import co.elastic.logstash.api.Password;
 import org.logstash.RubyUtil;
 
+/**
+ * Represents and decode credentials to access Elastic cloud instance.
+ * */
 public class CloudSettingAuth {
 
     private String original;
diff --git a/logstash-core/src/main/java/org/logstash/util/CloudSettingId.java b/logstash-core/src/main/java/org/logstash/util/CloudSettingId.java
index 4b432df1d..9fb6cd6f7 100644
--- a/logstash-core/src/main/java/org/logstash/util/CloudSettingId.java
+++ b/logstash-core/src/main/java/org/logstash/util/CloudSettingId.java
@@ -38,6 +38,9 @@ import java.util.Base64;
  * The third segment is the kibana host identifier, e.g. 'identifier'
  * The 'cloud.id' value decoded into the various fields.
  */
+/**
+ * Represents and decode an Elastic cloudid of an instance.
+ * */
 public class CloudSettingId {
 
     private static class HostAndPort {
diff --git a/logstash-core/src/main/java/org/logstash/util/ModulesSettingArray.java b/logstash-core/src/main/java/org/logstash/util/ModulesSettingArray.java
index f4f49c97b..f034e48f2 100644
--- a/logstash-core/src/main/java/org/logstash/util/ModulesSettingArray.java
+++ b/logstash-core/src/main/java/org/logstash/util/ModulesSettingArray.java
@@ -29,6 +29,10 @@ import java.util.Map;
 import java.util.TreeMap;
 import java.util.stream.Collectors;
 
+/**
+ * Wrapper of Logstash modules settings, with ability to replace password fields with
+ * the obfuscator {@link Password} implementation.
+ * */
 public final class ModulesSettingArray extends ArrayList<Map<String, Object>> {
 
     private static final long serialVersionUID = 4094949366274116593L;
diff --git a/logstash-core/src/main/java/org/logstash/util/TimeValue.java b/logstash-core/src/main/java/org/logstash/util/TimeValue.java
index 8ce4fcf88..479f17b7e 100644
--- a/logstash-core/src/main/java/org/logstash/util/TimeValue.java
+++ b/logstash-core/src/main/java/org/logstash/util/TimeValue.java
@@ -23,6 +23,9 @@ import org.logstash.RubyUtil;
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
+/**
+ * Express a period of time, expressing in numerical quantity and time unit, for example "3 seconds"
+ * */
 public class TimeValue {
 
     public static TimeValue fromValue(Object value) {
diff --git a/logstash-core/src/main/java/org/logstash/util/UtilExt.java b/logstash-core/src/main/java/org/logstash/util/UtilExt.java
index 6e85dd20f..bafdaa1db 100644
--- a/logstash-core/src/main/java/org/logstash/util/UtilExt.java
+++ b/logstash-core/src/main/java/org/logstash/util/UtilExt.java
@@ -26,6 +26,9 @@ import org.jruby.anno.JRubyModule;
 import org.jruby.runtime.ThreadContext;
 import org.jruby.runtime.builtin.IRubyObject;
 
+/**
+ * Utility methods class
+ * */
 @JRubyModule(name = "Util") // LogStash::Util
 public class UtilExt {