diff --git a/.gitignore b/.gitignore
index 90ccc9f..a8c2c2f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,6 +8,7 @@ composer.lock
 .hg
 .phpunit.result.cache
 .phpunit.cache
+temp
 
 # Commit your application's lock file https://getcomposer.org/doc/01-basic-usage.md#commit-your-composer-lock-file-to-version-control
 # You may choose to ignore a library lock file http://getcomposer.org/doc/02-libraries.md#lock-file
diff --git a/src/HydratorInterface.php b/src/HydratorInterface.php
new file mode 100644
index 0000000..f3fa749
--- /dev/null
+++ b/src/HydratorInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Andrey\JsonHandler;
+
+interface HydratorInterface
+{
+    public function hydrate(string|array $json, object|string $objOrClass): object;
+}
diff --git a/src/JsonHandler.php b/src/JsonHandler.php
deleted file mode 100644
index 12493c6..0000000
--- a/src/JsonHandler.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-
-namespace Andrey\JsonHandler;
-
-use JsonException;
-
-final class JsonHandler
-{
-    use JsonSerializerTrait;
-    use JsonHydratorTrait;
-
-    /**
-     * @throws JsonException
-     */
-    public static function Decode(string $json): array
-    {
-        return json_decode($json, true, 512, JSON_THROW_ON_ERROR);
-    }
-
-    /**
-     * @throws JsonException
-     */
-    public static function Encode(array $jsonArr): string
-    {
-        return json_encode($jsonArr, JSON_THROW_ON_ERROR);
-    }
-}
diff --git a/src/JsonHydratorTrait.php b/src/JsonHydrator.php
similarity index 74%
rename from src/JsonHydratorTrait.php
rename to src/JsonHydrator.php
index 8b044e1..a5dd4bf 100644
--- a/src/JsonHydratorTrait.php
+++ b/src/JsonHydrator.php
@@ -3,6 +3,8 @@
 
 use Andrey\JsonHandler\Attributes\JsonItemAttribute;
 use Andrey\JsonHandler\Attributes\JsonObjectAttribute;
+use Andrey\JsonHandler\KeyMapping\KeyMappingStrategy;
+use Andrey\JsonHandler\KeyMapping\KeyMappingUnderscore;
 use InvalidArgumentException;
 use JsonException;
 use LogicException;
@@ -10,49 +12,40 @@
 use ReflectionException;
 use ReflectionProperty;
 
-trait JsonHydratorTrait
+readonly class JsonHydrator implements HydratorInterface
 {
-    /**
-     * @throws JsonException
-     * @throws ReflectionException
-     */
-    public function hydrateObjectImmutable(string|array $json, object $obj): object
-    {
-        return $this->hydrateObject($json, clone $obj);
+    private KeyMappingStrategy $keyStrategy;
+
+    public function __construct(
+        ?KeyMappingStrategy $keyStrategy = null,
+    ) {
+        $this->keyStrategy = $keyStrategy ?: new KeyMappingUnderscore();
     }
 
     /**
      * @throws JsonException
      * @throws ReflectionException
      */
-    public function hydrateObject(string|array $json, object $obj): object
+    public function hydrate(string|array $json, object|string $objOrClass): object
     {
-        $jsonArr = is_string($json) ? JsonHandler::Decode($json) : $json;
-        $reflectionClass = new ReflectionClass($obj);
-        $data = $this->processClass($reflectionClass, $jsonArr);
-        if ($reflectionClass->hasMethod('hydrate')) {
-            $obj->hydrate($data);
-        } else {
-            foreach ($data as $key => $value) {
-                $obj->{$key} = $value;
-            }
-        }
-        return $obj;
+        $jsonArr = is_string($json) ? $this->decode($json) : $json;
+        $reflectionClass = new ReflectionClass($objOrClass);
+        return $this->processClass($reflectionClass, $jsonArr);
     }
 
     /**
      * @throws JsonException
      * @throws ReflectionException
      */
-    private function processClass(ReflectionClass $class, array $jsonArr): array
+    private function processClass(ReflectionClass $class, array $jsonArr): object
     {
+        $instance = $class->newInstance();
         $skipAttributeCheck = ($class->getAttributes(JsonObjectAttribute::class)[0] ?? null) !== null;
-        $output = [];
         $properties = $class->getProperties();
         foreach ($properties as $property) {
-            $output[$property->getName()] = $this->processProperty($property, $jsonArr, $skipAttributeCheck);
+            $property->setValue($instance, $this->processProperty($property, $jsonArr, $skipAttributeCheck));
         }
-        return $output;
+        return $instance;
     }
 
     /**
@@ -69,7 +62,7 @@ private function processProperty(ReflectionProperty $property, array $jsonArr, b
 
         /** @var JsonItemAttribute $item */
         $item = $attr?->newInstance() ?? new JsonItemAttribute();
-        $key = $item->key ?? $property->getName();
+        $key = $item->key ?? $this->keyStrategy->from($property->getName());
         if ($item->required && !array_key_exists($key, $jsonArr)) {
             throw new InvalidArgumentException(sprintf('required item <%s> not found', $key));
         }
@@ -114,9 +107,17 @@ private function handleCustomType(mixed $value, string $type): mixed
         if ($typeReflection->isEnum()) {
             return call_user_func($type.'::tryFrom', $value);
         }
-        return $this->hydrateObject(
+        return $this->hydrate(
             $value,
             new ($type)(),
         );
     }
+
+    /**
+     * @throws JsonException
+     */
+    private function decode(string $json): mixed
+    {
+        return json_decode($json, true, 512, JSON_THROW_ON_ERROR);
+    }
 }
diff --git a/src/JsonSerializerTrait.php b/src/JsonSerializer.php
similarity index 83%
rename from src/JsonSerializerTrait.php
rename to src/JsonSerializer.php
index 0436f36..37652af 100644
--- a/src/JsonSerializerTrait.php
+++ b/src/JsonSerializer.php
@@ -3,12 +3,22 @@
 
 use Andrey\JsonHandler\Attributes\JsonItemAttribute;
 use Andrey\JsonHandler\Attributes\JsonObjectAttribute;
+use Andrey\JsonHandler\KeyMapping\KeyMappingStrategy;
+use Andrey\JsonHandler\KeyMapping\KeyMappingUnderscore;
 use JsonException;
 use ReflectionClass;
 use ReflectionException;
 
-trait JsonSerializerTrait
+readonly class JsonSerializer implements SerializerInterface
 {
+    private KeyMappingStrategy $keyStrategy;
+
+    public function __construct(
+        ?KeyMappingStrategy $keyStrategy = null,
+    ) {
+        $this->keyStrategy = $keyStrategy ?: new KeyMappingUnderscore();
+    }
+
     /**
      * @throws ReflectionException
      * @throws JsonException
@@ -28,7 +38,7 @@ public function serialize(object $obj): array
             }
             /** @var JsonItemAttribute $item */
             $item = $attr?->newInstance() ?? new JsonItemAttribute();
-            $key = $item->key ?? $property->name;
+            $key = $item->key ?? $this->keyStrategy->from($property->name);
 
             if ($property->getType()?->isBuiltin()) {
                 $output[$key] = $this->handleArray($item, $property->getValue($obj));
diff --git a/src/KeyMapping/KeyMappingStrategy.php b/src/KeyMapping/KeyMappingStrategy.php
new file mode 100644
index 0000000..9791869
--- /dev/null
+++ b/src/KeyMapping/KeyMappingStrategy.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Andrey\JsonHandler\KeyMapping;
+
+interface KeyMappingStrategy
+{
+    // -> Hydrate
+    public function from(string $key): string;
+    // <- Parse
+    public function to(string $key): string;
+}
diff --git a/src/KeyMapping/KeyMappingUnderscore.php b/src/KeyMapping/KeyMappingUnderscore.php
new file mode 100644
index 0000000..4f42901
--- /dev/null
+++ b/src/KeyMapping/KeyMappingUnderscore.php
@@ -0,0 +1,60 @@
+<?php /** @noinspection ForeachInvariantsInspection */
+
+namespace Andrey\JsonHandler\KeyMapping;
+
+/**
+ *
+ */
+class KeyMappingUnderscore implements KeyMappingStrategy
+{
+    /**
+     * Map keys from pascalCase to underscore_case
+     *
+     */
+    public function from(string $key): string
+    {
+        $in = str_split($key);
+        $len = count($in);
+        $out = '';
+        for ($i = 0; $i < $len; $i++) {
+            if ($in[$i] < 'a') {
+                $out .= '_';
+                // if already is an underscore, just skip case conversion
+                // but still add another underscore before it
+                if ($in[$i] !== '_') {
+                    $out .= chr((ord($in[$i]) - ord('A')) + ord('a'));
+                } else {
+                    $out .= $in[$i];
+                }
+            } else {
+                $out .= $in[$i];
+            }
+        }
+        return $out;
+    }
+
+    public function to(string $key): string
+    {
+        $in = str_split($key);
+        $len = count($in);
+        $out = '';
+        // my_key => myKey
+        for ($i = 0; $i < $len; $i++) {
+            $c = $in[$i];
+            if ($c === '_') {
+                $c = $in[$i+1];
+                // jump to next letter (skip lowercase already dealt with)
+                $i++;
+                if ($c !== '_') {
+                    $out .= chr((ord($c) - ord('a')) + ord('A'));
+                } else {
+                    $out .= $c;
+                }
+            } else {
+                $out .= $c;
+            }
+        }
+
+        return $out;
+    }
+}
diff --git a/src/SerializerInterface.php b/src/SerializerInterface.php
new file mode 100644
index 0000000..d301117
--- /dev/null
+++ b/src/SerializerInterface.php
@@ -0,0 +1,8 @@
+<?php
+
+namespace Andrey\JsonHandler;
+
+interface SerializerInterface
+{
+    public function serialize(object $obj): array;
+}
diff --git a/tests/KeyMapping/KeyMappingUnderscoreTest.php b/tests/KeyMapping/KeyMappingUnderscoreTest.php
new file mode 100644
index 0000000..12a8c1b
--- /dev/null
+++ b/tests/KeyMapping/KeyMappingUnderscoreTest.php
@@ -0,0 +1,58 @@
+<?php
+namespace KeyMapping;
+
+use Andrey\JsonHandler\KeyMapping\KeyMappingUnderscore;
+use PHPUnit\Framework\Attributes\CoversTrait;
+use PHPUnit\Framework\TestCase;
+
+#[CoversTrait(KeyMappingUnderscore::class)]
+final class KeyMappingUnderscoreTest extends TestCase
+{
+    public function testFromKey(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->from('fromMyKey');
+        $this->assertEquals('from_my_key', $result);
+    }
+
+    public function testFromKeyStartingWithUnderscore(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->from('_fromMyKey');
+        $this->assertEquals('__from_my_key', $result);
+    }
+
+    /**
+     * For pascal case maintain behavior otherwise we cannot keep
+     * the equality (parser -> serializer and serializer -> parser)
+     *
+     * i.e. _from_my_key => FromMyKey but from_my_key => fromMyKey
+     */
+    public function testFromKeyPascalCase(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->from('FromMyKey');
+        $this->assertEquals('_from_my_key', $result);
+    }
+
+    public function testToKey(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->to('from_my_key');
+        $this->assertEquals('fromMyKey', $result);
+    }
+
+    public function testToKeyStartingWithUnderscore(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->to('__from_my_key');
+        $this->assertEquals('_fromMyKey', $result);
+    }
+
+    public function testToKeyPascalCase(): void
+    {
+        $strategy = new KeyMappingUnderscore();
+        $result = $strategy->to('_from_my_key');
+        $this->assertEquals('FromMyKey', $result);
+    }
+}