diff --git a/.gitignore b/.gitignore
index bffa164..be04972 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 .gradle
 .idea
+build
+.DS_Store
diff --git a/LICENSE b/LICENSE
index a9d48b9..3b45d71 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2021 Artur Aukhatov
+Copyright (c) 2022 PepperKit
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
diff --git a/README.md b/README.md
index b9f4bd0..bdde4ab 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ new BackoffFunction.Exponential(3);
 ```
 
 #### Fixed
-This is an elementary implementation, just return a constant value.
+This is an elementary implementation, it just returns a constant value.
 ```text
 3s -> 3s -> 3s -> 3s
 ```
diff --git a/build.gradle b/build.gradle
index 3b80e2b..8febba0 100644
--- a/build.gradle
+++ b/build.gradle
@@ -51,9 +51,9 @@ test {
 }
 
 checkstyle {
-    toolVersion '8.42'
+    toolVersion '9.2.1'
     config project.resources.text
-            .fromUri(new URI("https://raw.githubusercontent.com/pepperkit/checkstyle/v1.0.0-8.45/checkstyle.xml"))
+            .fromUri(new URI("https://raw.githubusercontent.com/pepperkit/checkstyle/v1.0.2-9.2/checkstyle.xml"))
 }
 
 tasks.withType(Javadoc) {
diff --git a/src/main/java/io/github/pepperkit/retry/BackoffFunction.java b/src/main/java/io/github/pepperkit/retry/BackoffFunction.java
index f6d8408..c4ff28c 100644
--- a/src/main/java/io/github/pepperkit/retry/BackoffFunction.java
+++ b/src/main/java/io/github/pepperkit/retry/BackoffFunction.java
@@ -1,13 +1,25 @@
+/*
+ * Copyright (C) 2022 PepperKit
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license. See the LICENSE file for details.
+ */
 package io.github.pepperkit.retry;
 
 import java.security.SecureRandom;
 import java.time.Duration;
 
+/**
+ * The backoff function determines how much to wait between the retries.
+ */
 @FunctionalInterface
 public interface BackoffFunction {
 
     Duration delay(int attempt, Duration delay);
 
+    /**
+     * An elementary implementation of a backoff function, just returns a constant value.
+     */
     class Fixed implements BackoffFunction {
 
         public Fixed() {
@@ -20,11 +32,15 @@ public Duration delay(int attempt, Duration delay) {
         }
     }
 
+    /**
+     * Exponential backoff function waits progressively longer intervals between subsequent retries.
+     */
     class Exponential implements BackoffFunction {
 
         private static final int DEFAULT_FACTOR = 3;
         private final int factor;
 
+
         public Exponential(int factor) {
             if (factor < 1) {
                 throw new IllegalArgumentException("Factor must be greater than 1");
@@ -45,6 +61,9 @@ public Duration delay(int attempt, Duration delay) {
         }
     }
 
+    /**
+     * Randomized backoff algorithm implementation, each interval value is determined randomly.
+     */
     class Randomized implements BackoffFunction {
 
         private final int bound;
diff --git a/src/main/java/io/github/pepperkit/retry/CallableRetry.java b/src/main/java/io/github/pepperkit/retry/CallableRetry.java
index d3ae873..4b52d40 100644
--- a/src/main/java/io/github/pepperkit/retry/CallableRetry.java
+++ b/src/main/java/io/github/pepperkit/retry/CallableRetry.java
@@ -1,5 +1,15 @@
+/*
+ * Copyright (C) 2022 PepperKit
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license. See the LICENSE file for details.
+ */
 package io.github.pepperkit.retry;
 
+/**
+ * Callable version of a retry action.
+ * @param <V> the type of returned value
+ */
 public interface CallableRetry<V> {
 
     /**
diff --git a/src/main/java/io/github/pepperkit/retry/Retry.java b/src/main/java/io/github/pepperkit/retry/Retry.java
index 0e4735a..22f0131 100644
--- a/src/main/java/io/github/pepperkit/retry/Retry.java
+++ b/src/main/java/io/github/pepperkit/retry/Retry.java
@@ -1,3 +1,9 @@
+/*
+ * Copyright (C) 2022 PepperKit
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license. See the LICENSE file for details.
+ */
 package io.github.pepperkit.retry;
 
 import java.time.Duration;
@@ -8,6 +14,9 @@
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 
+/**
+ * A static interface for the Retry library.
+ */
 public final class Retry {
 
     private static final int DEFAULT_MAX_ATTEMPTS = 3;
diff --git a/src/main/java/io/github/pepperkit/retry/RetryInterruptedException.java b/src/main/java/io/github/pepperkit/retry/RetryInterruptedException.java
index 1597667..268a8e1 100644
--- a/src/main/java/io/github/pepperkit/retry/RetryInterruptedException.java
+++ b/src/main/java/io/github/pepperkit/retry/RetryInterruptedException.java
@@ -1,5 +1,14 @@
+/*
+ * Copyright (C) 2022 PepperKit
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license. See the LICENSE file for details.
+ */
 package io.github.pepperkit.retry;
 
+/**
+ * Exception, which occurs if retry attempt was interrupted.
+ */
 public class RetryInterruptedException extends RuntimeException {
 
     private static final long serialVersionUID = 5443040601324416580L;
diff --git a/src/main/java/io/github/pepperkit/retry/RunnableRetry.java b/src/main/java/io/github/pepperkit/retry/RunnableRetry.java
index ea5c9c2..c5680d8 100644
--- a/src/main/java/io/github/pepperkit/retry/RunnableRetry.java
+++ b/src/main/java/io/github/pepperkit/retry/RunnableRetry.java
@@ -1,5 +1,14 @@
+/*
+ * Copyright (C) 2022 PepperKit
+ *
+ * This software may be modified and distributed under the terms
+ * of the MIT license. See the LICENSE file for details.
+ */
 package io.github.pepperkit.retry;
 
+/**
+ * Runnable version of a retry action.
+ */
 public interface RunnableRetry {
 
     /**