diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 7a03f78..721c962 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -28,6 +28,13 @@ class Configuration implements ConfigurationInterface
                     ->children()
                         ->scalarNode('enabled')->defaultTrue()->end()
                         ->scalarNode('endpoint')->defaultValue('/app_dev.php')->end()
+                        ->scalarNode('json_declaration_method')
+                            ->defaultValue('format_param')
+                            ->validate()
+                                ->ifNotInArray(array('format_param', 'accept_header'))
+                                ->thenInvalid("Unknown json declaration method '%s'.")
+                            ->end()
+                        ->end()
                         ->arrayNode('authentication')
                             ->children()
                                 ->scalarNode('name')->isRequired()->end()
diff --git a/DependencyInjection/NelmioApiDocExtension.php b/DependencyInjection/NelmioApiDocExtension.php
index 321a2cc..1852fcf 100644
--- a/DependencyInjection/NelmioApiDocExtension.php
+++ b/DependencyInjection/NelmioApiDocExtension.php
@@ -31,6 +31,7 @@ class NelmioApiDocExtension extends Extension
         $container->setParameter('nelmio_api_doc.api_name', $config['name']);
         $container->setParameter('nelmio_api_doc.sandbox.enabled',  $config['sandbox']['enabled']);
         $container->setParameter('nelmio_api_doc.sandbox.endpoint', $config['sandbox']['endpoint']);
+        $container->setParameter('nelmio_api_doc.sandbox.json_declaration_method', $config['sandbox']['json_declaration_method']);
 
         $loader = new XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('formatters.xml');
diff --git a/Formatter/HtmlFormatter.php b/Formatter/HtmlFormatter.php
index 0e570c7..5c1dd30 100644
--- a/Formatter/HtmlFormatter.php
+++ b/Formatter/HtmlFormatter.php
@@ -40,6 +40,11 @@ class HtmlFormatter extends AbstractFormatter
      */
     private $engine;
 
+    /**
+     * @var string
+     */
+    private $jsonDeclarationMethod;
+
     /**
      * @param array $authentication
      */
@@ -80,6 +85,14 @@ class HtmlFormatter extends AbstractFormatter
         $this->engine = $engine;
     }
 
+    /**
+     * @param string $method
+     */
+    public function setJsonDeclarationMethod($method)
+    {
+        $this->jsonDeclarationMethod = $method;
+    }
+
     /**
      * {@inheritdoc}
      */
@@ -133,13 +146,14 @@ class HtmlFormatter extends AbstractFormatter
     private function getGlobalVars()
     {
         return array(
-            'apiName'        => $this->apiName,
-            'authentication' => $this->authentication,
-            'endpoint'       => $this->endpoint,
-            'enableSandbox'  => $this->enableSandbox,
-            'date'           => date(DATE_RFC822),
-            'css'            => file_get_contents(__DIR__ . '/../Resources/public/css/screen.css'),
-            'js'             => file_get_contents(__DIR__ . '/../Resources/public/js/all.js'),
+            'apiName'               => $this->apiName,
+            'authentication'        => $this->authentication,
+            'endpoint'              => $this->endpoint,
+            'enableSandbox'         => $this->enableSandbox,
+            'jsonDeclarationMethod' => $this->jsonDeclarationMethod,
+            'date'                  => date(DATE_RFC822),
+            'css'                   => file_get_contents(__DIR__ . '/../Resources/public/css/screen.css'),
+            'js'                    => file_get_contents(__DIR__ . '/../Resources/public/js/all.js'),
         );
     }
 
diff --git a/Resources/config/formatters.xml b/Resources/config/formatters.xml
index bc1dcbf..60373b5 100644
--- a/Resources/config/formatters.xml
+++ b/Resources/config/formatters.xml
@@ -37,6 +37,9 @@
             <call method="setEndpoint">
                 <argument>%nelmio_api_doc.sandbox.endpoint%</argument>
             </call>
+            <call method="setJsonDeclarationMethod">
+                <argument>%nelmio_api_doc.sandbox.json_declaration_method%</argument>
+            </call>
             <call method="setAuthentication">
                 <argument>%nelmio_api_doc.sandbox.authentication%</argument>
             </call>
diff --git a/Resources/views/layout.html.twig b/Resources/views/layout.html.twig
index 306befb..95cd134 100644
--- a/Resources/views/layout.html.twig
+++ b/Resources/views/layout.html.twig
@@ -134,13 +134,18 @@
                     var url = $(this).attr('action'),
                         method = $(this).attr('method'),
                         self = this,
-                        params = {
-                            _format: 'json' // default format if not overriden in the form
-                        },
+                        params = {},
                         headers = {},
                         content = $(this).find('textarea.content').val();
                         result_container = $('.result', $(this).parent());
 
+                    var jsonDeclarationMethod = '{{ jsonDeclarationMethod }}';
+                    if (jsonDeclarationMethod == 'format_param') {
+                        params['_format'] = 'json';
+                    } else if (jsonDeclarationMethod == 'accept_header') {
+                        headers['Accept'] = 'application/json';
+                    }
+
                     // retrieve all the parameters to send
                     $('.parameters .tuple', $(this)).each(function() {
                     var key, value;