diff --git a/README.md b/README.md
index 9548d8d..20acd78 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,10 @@ Chaos Monkey for Symfony applications. Try to attack your running Symfony App.
  - Repository (not implemented)
  - Service (not implemented)
 
+## Activators
+
+ - "Query param" - attack only if given query param is present (default `chaos`)
+
 ## Symfony 
 
 ## How to use
@@ -62,10 +66,12 @@ chaos_monkey:
         request:
             enabled: true
             priority: 0
+    activators:
+       query_param: false # if true then chaos monkey will be called only if given query param exist (with any value)
+       query_param_name: 'chaos'
 ```
 
 ## Roadmap
- - [ ] Query param activator
  - [ ] Flex recipe
  - [ ] Metrics (for example `chaos_monkey_request_count_assaulted`)
  - [ ] Assault profiles - each profile can contain different assaults
diff --git a/src/Activator/QueryParamActivator.php b/src/Activator/QueryParamActivator.php
new file mode 100644
index 0000000..6a7c576
--- /dev/null
+++ b/src/Activator/QueryParamActivator.php
@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Chaos\Monkey\Symfony\Activator;
+
+use Symfony\Component\HttpFoundation\Request;
+
+final class QueryParamActivator
+{
+    public function __construct(private readonly bool $enabled = false, private readonly string $paramName = 'chaos')
+    {
+    }
+
+    public function inChaos(Request $request): bool
+    {
+        if (!$this->enabled) {
+            return true;
+        }
+
+        return $request->query->has($this->paramName);
+    }
+}
diff --git a/src/DependencyInjection/ChaosMonkeyExtension.php b/src/DependencyInjection/ChaosMonkeyExtension.php
index 662462a..cd56f07 100644
--- a/src/DependencyInjection/ChaosMonkeyExtension.php
+++ b/src/DependencyInjection/ChaosMonkeyExtension.php
@@ -21,6 +21,10 @@
  *     },
  *     watchers: array{
  *      request: array{enabled: bool, priority: int}
+ *     },
+ *     activators: array{
+ *      query_param: bool,
+ *      query_param_name: string
  *     }
  * }
  */
@@ -39,6 +43,7 @@ public function load(array $configs, ContainerBuilder $container): void
         $config = $this->processConfiguration($configuration, $configs);
 
         $this->setChaosMonkeySettings($container, $config);
+        $this->setActivators($container, $config);
         $this->enableWatchers($container, $config);
     }
 
@@ -77,4 +82,16 @@ private function enableWatchers(ContainerBuilder $container, array $config): voi
             ]);
         }
     }
+
+    /**
+     * @param ConfigArray $config
+     */
+    private function setActivators(ContainerBuilder $container, array $config): void
+    {
+        $queryParam = $container->getDefinition('chaos_monkey.activator.query_param');
+        $queryParam->setArguments([
+            '$enabled' => $config['activators']['query_param'],
+            '$paramName' => $config['activators']['query_param_name'],
+        ]);
+    }
 }
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index c940b5f..e19b23e 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -65,6 +65,13 @@ public function getConfigTreeBuilder(): TreeBuilder
                     ->end()
                 ->end()
             ->end()
+            ->arrayNode('activators')
+                ->addDefaultsIfNotSet()
+                ->children()
+                    ->booleanNode('query_param')->defaultFalse()->end()
+                    ->scalarNode('query_param_name')->defaultValue('chaos')->end()
+                ->end()
+            ->end()
         ->end();
 
         return $treeBuilder;
diff --git a/src/Resources/config/services.xml b/src/Resources/config/services.xml
index ebf6787..95f1375 100644
--- a/src/Resources/config/services.xml
+++ b/src/Resources/config/services.xml
@@ -14,6 +14,10 @@
 
         <service id="chaos_monkey.watcher.request" class="Chaos\Monkey\Symfony\Watcher\RequestWatcher" public="false">
             <argument type="service" id="chaos_monkey" />
+            <argument type="service" id="chaos_monkey.activator.query_param" />
+        </service>
+
+        <service id="chaos_monkey.activator.query_param" class="Chaos\Monkey\Symfony\Activator\QueryParamActivator" public="false">
         </service>
 
         <instanceof id="Chaos\Monkey\Assault" autowire="true">
diff --git a/src/Watcher/RequestWatcher.php b/src/Watcher/RequestWatcher.php
index 228521c..08597e0 100644
--- a/src/Watcher/RequestWatcher.php
+++ b/src/Watcher/RequestWatcher.php
@@ -5,15 +5,15 @@
 namespace Chaos\Monkey\Symfony\Watcher;
 
 use Chaos\Monkey\ChaosMonkey;
+use Chaos\Monkey\Symfony\Activator\QueryParamActivator;
 use Symfony\Component\HttpKernel\Event\RequestEvent;
 
-class RequestWatcher
+final class RequestWatcher
 {
-    private ChaosMonkey $chaosMonkey;
-
-    public function __construct(ChaosMonkey $chaosMonkey)
-    {
-        $this->chaosMonkey = $chaosMonkey;
+    public function __construct(
+        private readonly ChaosMonkey $chaosMonkey,
+        private readonly QueryParamActivator $queryParamActivator
+    ) {
     }
 
     public function onKernelRequest(RequestEvent $event): void
@@ -22,6 +22,8 @@ public function onKernelRequest(RequestEvent $event): void
             return;
         }
 
-        $this->chaosMonkey->call();
+        if ($this->queryParamActivator->inChaos($event->getRequest())) {
+            $this->chaosMonkey->call();
+        }
     }
 }
diff --git a/tests/Activator/QueryParamActivatorTest.php b/tests/Activator/QueryParamActivatorTest.php
new file mode 100644
index 0000000..ae48104
--- /dev/null
+++ b/tests/Activator/QueryParamActivatorTest.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Chaos\Monkey\Symfony\Tests\Activator;
+
+use Chaos\Monkey\Symfony\Activator\QueryParamActivator;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpFoundation\Request;
+
+final class QueryParamActivatorTest extends TestCase
+{
+    public function testItIsInChaosIfDisabled(): void
+    {
+        $activator = new QueryParamActivator();
+
+        self::assertTrue($activator->inChaos(new Request()));
+    }
+
+    public function testItIsNoInChaosIfEnabledAndParamMissing(): void
+    {
+        $activator = new QueryParamActivator(true);
+
+        self::assertFalse($activator->inChaos(new Request()));
+    }
+
+    public function testItIsInChaosIfEnabledAndParamExists(): void
+    {
+        $activator = new QueryParamActivator(true, 'bye');
+
+        self::assertTrue($activator->inChaos(new Request(['bye' => true])));
+    }
+}
diff --git a/tests/Controller/SymfonyControllerTest.php b/tests/Controller/SymfonyControllerTest.php
index d4fcdf8..c6760ec 100644
--- a/tests/Controller/SymfonyControllerTest.php
+++ b/tests/Controller/SymfonyControllerTest.php
@@ -5,9 +5,11 @@
 namespace Chaos\Monkey\Symfony\Tests\Controller;
 
 use Chaos\Monkey\Settings;
+use Chaos\Monkey\Symfony\Activator\QueryParamActivator;
 use Chaos\Monkey\Symfony\Tests\Symfony\Kernel;
 use PHPUnit\Framework\TestCase;
 use Symfony\Bundle\FrameworkBundle\KernelBrowser;
+use Symfony\Component\HttpKernel\Exception\LockedHttpException;
 use Symfony\Component\Stopwatch\Stopwatch;
 
 class SymfonyControllerTest extends TestCase
@@ -49,7 +51,22 @@ public function testRequestExceptionAttack(): void
         $this->enableExceptionAssault();
         $this->client->request('GET', '/hello');
 
-        self::assertEquals(500, $this->client->getResponse()->getStatusCode());
+        self::assertEquals(423, $this->client->getResponse()->getStatusCode());
+
+        $this->disableExceptionAssault();
+    }
+
+    public function testRequestExceptionAttackWithQueryParamActivatorEnabled(): void
+    {
+        $this->enableQueryParamActivator();
+        $this->enableExceptionAssault();
+        $this->client->request('GET', '/hello');
+
+        self::assertEquals(200, $this->client->getResponse()->getStatusCode());
+
+        $this->client->request('GET', '/hello?chaos=true');
+
+        self::assertEquals(423, $this->client->getResponse()->getStatusCode());
 
         $this->disableExceptionAssault();
     }
@@ -58,6 +75,7 @@ private function enableExceptionAssault(): void
     {
         $this->chaosMonkeySettings()->setEnabled(true);
         $this->chaosMonkeySettings()->setExceptionActive(true);
+        $this->chaosMonkeySettings()->setExceptionClass(LockedHttpException::class);
         $this->chaosMonkeySettings()->setProbability(100);
     }
 
@@ -84,4 +102,9 @@ private function chaosMonkeySettings(): Settings
     {
         return $this->client->getContainer()->get('chaos_monkey')->settings();
     }
+
+    private function enableQueryParamActivator(): void
+    {
+        $this->client->getContainer()->get('test.service_container')->set('chaos_monkey.activator.query_param', new QueryParamActivator(true));
+    }
 }
diff --git a/tests/Symfony/Kernel.php b/tests/Symfony/Kernel.php
index c2ba8ed..7aade88 100644
--- a/tests/Symfony/Kernel.php
+++ b/tests/Symfony/Kernel.php
@@ -29,6 +29,7 @@ protected function configureContainer(ContainerConfigurator $container): void
     {
         $container->extension('framework', [
             'secret' => 'S0ME_SECRET',
+            'test' => true,
         ]);
 
         $container->services()->set('logger', NullLogger::class);