diff --git a/src/Platform/Bridge/Anthropic/Contract/AnthropicContract.php b/src/Platform/Bridge/Anthropic/Contract/AnthropicContract.php
new file mode 100644
index 00000000..40dabf6a
--- /dev/null
+++ b/src/Platform/Bridge/Anthropic/Contract/AnthropicContract.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract;
+
+use PhpLlm\LlmChain\Platform\Contract;
+use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+
+/**
+ * @author Denis Zunke <denis.zunke@gmail.com>
+ */
+final readonly class AnthropicContract extends Contract
+{
+    public static function create(NormalizerInterface ...$normalizer): Contract
+    {
+        return parent::create(
+            new AssistantMessageNormalizer(),
+            new DocumentNormalizer(),
+            new DocumentUrlNormalizer(),
+            new ImageNormalizer(),
+            new ImageUrlNormalizer(),
+            new MessageBagNormalizer(),
+            new ToolCallMessageNormalizer(),
+            new ToolNormalizer(),
+            ...$normalizer,
+        );
+    }
+}
diff --git a/src/Platform/Bridge/Anthropic/PlatformFactory.php b/src/Platform/Bridge/Anthropic/PlatformFactory.php
index 87abe1f5..dbb6abc3 100644
--- a/src/Platform/Bridge/Anthropic/PlatformFactory.php
+++ b/src/Platform/Bridge/Anthropic/PlatformFactory.php
@@ -4,14 +4,7 @@
 
 namespace PhpLlm\LlmChain\Platform\Bridge\Anthropic;
 
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\AssistantMessageNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\DocumentNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\DocumentUrlNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\ImageNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\ImageUrlNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\MessageBagNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\ToolCallMessageNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\ToolNormalizer;
+use PhpLlm\LlmChain\Platform\Bridge\Anthropic\Contract\AnthropicContract;
 use PhpLlm\LlmChain\Platform\Contract;
 use PhpLlm\LlmChain\Platform\Platform;
 use Symfony\Component\HttpClient\EventSourceHttpClient;
@@ -27,22 +20,14 @@ public static function create(
         string $apiKey,
         string $version = '2023-06-01',
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
 
         return new Platform(
             [new ModelClient($httpClient, $apiKey, $version)],
             [new ResponseConverter()],
-            Contract::create(
-                new AssistantMessageNormalizer(),
-                new DocumentNormalizer(),
-                new DocumentUrlNormalizer(),
-                new ImageNormalizer(),
-                new ImageUrlNormalizer(),
-                new MessageBagNormalizer(),
-                new ToolCallMessageNormalizer(),
-                new ToolNormalizer(),
-            )
+            $contract ?? AnthropicContract::create(),
         );
     }
 }
diff --git a/src/Platform/Bridge/Azure/Meta/PlatformFactory.php b/src/Platform/Bridge/Azure/Meta/PlatformFactory.php
index 51e4c3d5..a63ef001 100644
--- a/src/Platform/Bridge/Azure/Meta/PlatformFactory.php
+++ b/src/Platform/Bridge/Azure/Meta/PlatformFactory.php
@@ -4,6 +4,7 @@
 
 namespace PhpLlm\LlmChain\Platform\Bridge\Azure\Meta;
 
+use PhpLlm\LlmChain\Platform\Contract;
 use PhpLlm\LlmChain\Platform\Platform;
 use Symfony\Component\HttpClient\HttpClient;
 use Symfony\Contracts\HttpClient\HttpClientInterface;
@@ -18,9 +19,10 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $modelClient = new LlamaHandler($httpClient ?? HttpClient::create(), $baseUrl, $apiKey);
 
-        return new Platform([$modelClient], [$modelClient]);
+        return new Platform([$modelClient], [$modelClient], $contract);
     }
 }
diff --git a/src/Platform/Bridge/Azure/OpenAI/PlatformFactory.php b/src/Platform/Bridge/Azure/OpenAI/PlatformFactory.php
index 6e4e1288..86c58423 100644
--- a/src/Platform/Bridge/Azure/OpenAI/PlatformFactory.php
+++ b/src/Platform/Bridge/Azure/OpenAI/PlatformFactory.php
@@ -24,6 +24,7 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
         $embeddingsResponseFactory = new EmbeddingsModelClient($httpClient, $baseUrl, $deployment, $apiVersion, $apiKey);
@@ -33,7 +34,7 @@ public static function create(
         return new Platform(
             [$GPTResponseFactory, $embeddingsResponseFactory, $whisperResponseFactory],
             [new ResponseConverter(), new Embeddings\ResponseConverter(), new \PhpLlm\LlmChain\Platform\Bridge\OpenAI\Whisper\ResponseConverter()],
-            Contract::create(new AudioNormalizer()),
+            $contract ?? Contract::create(new AudioNormalizer()),
         );
     }
 }
diff --git a/src/Platform/Bridge/Bedrock/PlatformFactory.php b/src/Platform/Bridge/Bedrock/PlatformFactory.php
index e2315682..113aee7e 100644
--- a/src/Platform/Bridge/Bedrock/PlatformFactory.php
+++ b/src/Platform/Bridge/Bedrock/PlatformFactory.php
@@ -8,6 +8,7 @@
 use PhpLlm\LlmChain\Platform\Bridge\Bedrock\Anthropic\ClaudeHandler;
 use PhpLlm\LlmChain\Platform\Bridge\Bedrock\Meta\LlamaModelClient;
 use PhpLlm\LlmChain\Platform\Bridge\Bedrock\Nova\NovaHandler;
+use PhpLlm\LlmChain\Platform\Contract;
 
 /**
  * @author Björn Altmann
@@ -16,11 +17,12 @@
 {
     public static function create(
         BedrockRuntimeClient $bedrockRuntimeClient = new BedrockRuntimeClient(),
+        ?Contract $contract = null,
     ): Platform {
         $modelClient[] = new ClaudeHandler($bedrockRuntimeClient);
         $modelClient[] = new NovaHandler($bedrockRuntimeClient);
         $modelClient[] = new LlamaModelClient($bedrockRuntimeClient);
 
-        return new Platform($modelClient);
+        return new Platform($modelClient, $contract);
     }
 }
diff --git a/src/Platform/Bridge/Google/Contract/GoogleContract.php b/src/Platform/Bridge/Google/Contract/GoogleContract.php
new file mode 100644
index 00000000..fcf6c990
--- /dev/null
+++ b/src/Platform/Bridge/Google/Contract/GoogleContract.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpLlm\LlmChain\Platform\Bridge\Google\Contract;
+
+use PhpLlm\LlmChain\Platform\Contract;
+use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
+
+/**
+ * @author Denis Zunke <denis.zunke@gmail.com>
+ */
+final readonly class GoogleContract extends Contract
+{
+    public static function create(NormalizerInterface ...$normalizer): Contract
+    {
+        return parent::create(
+            new AssistantMessageNormalizer(),
+            new MessageBagNormalizer(),
+            new ToolNormalizer(),
+            new ToolCallMessageNormalizer(),
+            new UserMessageNormalizer(),
+            ...$normalizer,
+        );
+    }
+}
diff --git a/src/Platform/Bridge/Google/PlatformFactory.php b/src/Platform/Bridge/Google/PlatformFactory.php
index da224f29..4fc927c4 100644
--- a/src/Platform/Bridge/Google/PlatformFactory.php
+++ b/src/Platform/Bridge/Google/PlatformFactory.php
@@ -4,11 +4,7 @@
 
 namespace PhpLlm\LlmChain\Platform\Bridge\Google;
 
-use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\AssistantMessageNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\MessageBagNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\ToolCallMessageNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\ToolNormalizer;
-use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\UserMessageNormalizer;
+use PhpLlm\LlmChain\Platform\Bridge\Google\Contract\GoogleContract;
 use PhpLlm\LlmChain\Platform\Bridge\Google\Embeddings\ModelClient;
 use PhpLlm\LlmChain\Platform\Contract;
 use PhpLlm\LlmChain\Platform\Platform;
@@ -24,17 +20,16 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
         $responseHandler = new ModelHandler($httpClient, $apiKey);
         $embeddings = new ModelClient($httpClient, $apiKey);
 
-        return new Platform([$responseHandler, $embeddings], [$responseHandler, $embeddings], Contract::create(
-            new AssistantMessageNormalizer(),
-            new MessageBagNormalizer(),
-            new ToolNormalizer(),
-            new ToolCallMessageNormalizer(),
-            new UserMessageNormalizer(),
-        ));
+        return new Platform(
+            [$responseHandler, $embeddings],
+            [$responseHandler, $embeddings],
+            $contract ?? GoogleContract::create(),
+        );
     }
 }
diff --git a/src/Platform/Bridge/HuggingFace/PlatformFactory.php b/src/Platform/Bridge/HuggingFace/PlatformFactory.php
index e46ae69a..d71b4e22 100644
--- a/src/Platform/Bridge/HuggingFace/PlatformFactory.php
+++ b/src/Platform/Bridge/HuggingFace/PlatformFactory.php
@@ -21,13 +21,14 @@ public static function create(
         string $apiKey,
         string $provider = Provider::HF_INFERENCE,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
 
         return new Platform(
             [new ModelClient($httpClient, $provider, $apiKey)],
             [new ResponseConverter()],
-            Contract::create(
+            $contract ?? Contract::create(
                 new FileNormalizer(),
                 new MessageBagNormalizer(),
             ),
diff --git a/src/Platform/Bridge/Mistral/PlatformFactory.php b/src/Platform/Bridge/Mistral/PlatformFactory.php
index 47ab83a0..436597f6 100644
--- a/src/Platform/Bridge/Mistral/PlatformFactory.php
+++ b/src/Platform/Bridge/Mistral/PlatformFactory.php
@@ -23,13 +23,14 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
 
         return new Platform(
             [new EmbeddingsModelClient($httpClient, $apiKey), new MistralModelClient($httpClient, $apiKey)],
             [new EmbeddingsResponseConverter(), new MistralResponseConverter()],
-            Contract::create(new ToolNormalizer()),
+            $contract ?? Contract::create(new ToolNormalizer()),
         );
     }
 }
diff --git a/src/Platform/Bridge/Ollama/PlatformFactory.php b/src/Platform/Bridge/Ollama/PlatformFactory.php
index c07e9699..5926aeb9 100644
--- a/src/Platform/Bridge/Ollama/PlatformFactory.php
+++ b/src/Platform/Bridge/Ollama/PlatformFactory.php
@@ -4,6 +4,7 @@
 
 namespace PhpLlm\LlmChain\Platform\Bridge\Ollama;
 
+use PhpLlm\LlmChain\Platform\Contract;
 use PhpLlm\LlmChain\Platform\Platform;
 use Symfony\Component\HttpClient\EventSourceHttpClient;
 use Symfony\Contracts\HttpClient\HttpClientInterface;
@@ -16,10 +17,11 @@ final class PlatformFactory
     public static function create(
         string $hostUrl = 'http://localhost:11434',
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
         $handler = new LlamaModelHandler($httpClient, $hostUrl);
 
-        return new Platform([$handler], [$handler]);
+        return new Platform([$handler], [$handler], $contract);
     }
 }
diff --git a/src/Platform/Bridge/OpenAI/PlatformFactory.php b/src/Platform/Bridge/OpenAI/PlatformFactory.php
index f27c76b7..5531fbfe 100644
--- a/src/Platform/Bridge/OpenAI/PlatformFactory.php
+++ b/src/Platform/Bridge/OpenAI/PlatformFactory.php
@@ -26,6 +26,7 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
 
@@ -44,7 +45,7 @@ public static function create(
                 $dallEModelClient,
                 new WhisperResponseConverter(),
             ],
-            Contract::create(new AudioNormalizer()),
+            $contract ?? Contract::create(new AudioNormalizer()),
         );
     }
 }
diff --git a/src/Platform/Bridge/OpenRouter/PlatformFactory.php b/src/Platform/Bridge/OpenRouter/PlatformFactory.php
index bd0cb684..cc988748 100644
--- a/src/Platform/Bridge/OpenRouter/PlatformFactory.php
+++ b/src/Platform/Bridge/OpenRouter/PlatformFactory.php
@@ -21,14 +21,19 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
         $handler = new Client($httpClient, $apiKey);
 
-        return new Platform([$handler], [$handler], Contract::create(
-            new AssistantMessageNormalizer(),
-            new MessageBagNormalizer(),
-            new UserMessageNormalizer(),
-        ));
+        return new Platform(
+            [$handler],
+            [$handler],
+            $contract ?? Contract::create(
+                new AssistantMessageNormalizer(),
+                new MessageBagNormalizer(),
+                new UserMessageNormalizer(),
+            ),
+        );
     }
 }
diff --git a/src/Platform/Bridge/Replicate/PlatformFactory.php b/src/Platform/Bridge/Replicate/PlatformFactory.php
index f150ff0a..12f0553e 100644
--- a/src/Platform/Bridge/Replicate/PlatformFactory.php
+++ b/src/Platform/Bridge/Replicate/PlatformFactory.php
@@ -20,11 +20,12 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         return new Platform(
             [new LlamaModelClient(new Client($httpClient ?? HttpClient::create(), new Clock(), $apiKey))],
             [new LlamaResponseConverter()],
-            Contract::create(new LlamaMessageBagNormalizer()),
+            $contract ?? Contract::create(new LlamaMessageBagNormalizer()),
         );
     }
 }
diff --git a/src/Platform/Bridge/Voyage/PlatformFactory.php b/src/Platform/Bridge/Voyage/PlatformFactory.php
index f4bb9ec6..ea8359f6 100644
--- a/src/Platform/Bridge/Voyage/PlatformFactory.php
+++ b/src/Platform/Bridge/Voyage/PlatformFactory.php
@@ -4,6 +4,7 @@
 
 namespace PhpLlm\LlmChain\Platform\Bridge\Voyage;
 
+use PhpLlm\LlmChain\Platform\Contract;
 use PhpLlm\LlmChain\Platform\Platform;
 use Symfony\Component\HttpClient\EventSourceHttpClient;
 use Symfony\Contracts\HttpClient\HttpClientInterface;
@@ -17,10 +18,11 @@ public static function create(
         #[\SensitiveParameter]
         string $apiKey,
         ?HttpClientInterface $httpClient = null,
+        ?Contract $contract = null,
     ): Platform {
         $httpClient = $httpClient instanceof EventSourceHttpClient ? $httpClient : new EventSourceHttpClient($httpClient);
         $handler = new ModelHandler($httpClient, $apiKey);
 
-        return new Platform([$handler], [$handler]);
+        return new Platform([$handler], [$handler], $contract);
     }
 }
diff --git a/src/Platform/Contract.php b/src/Platform/Contract.php
index dff53424..775ed91c 100644
--- a/src/Platform/Contract.php
+++ b/src/Platform/Contract.php
@@ -23,12 +23,12 @@
 /**
  * @author Christopher Hertel <mail@christopher-hertel.de>
  */
-final readonly class Contract
+readonly class Contract
 {
     public const CONTEXT_MODEL = 'model';
 
-    public function __construct(
-        private NormalizerInterface $normalizer,
+    final public function __construct(
+        protected NormalizerInterface $normalizer,
     ) {
     }
 
@@ -63,7 +63,7 @@ public static function create(NormalizerInterface ...$normalizer): self
      *
      * @return array<string, mixed>|string
      */
-    public function createRequestPayload(Model $model, object|array|string $input): string|array
+    final public function createRequestPayload(Model $model, object|array|string $input): string|array
     {
         return $this->normalizer->normalize($input, context: [self::CONTEXT_MODEL => $model]);
     }
@@ -73,7 +73,7 @@ public function createRequestPayload(Model $model, object|array|string $input):
      *
      * @return array<string, mixed>
      */
-    public function createToolOption(array $tools, Model $model): array
+    final public function createToolOption(array $tools, Model $model): array
     {
         return $this->normalizer->normalize($tools, context: [self::CONTEXT_MODEL => $model, AbstractObjectNormalizer::PRESERVE_EMPTY_OBJECTS => true]);
     }