diff --git a/README.md b/README.md
index ba37294..8718f50 100644
--- a/README.md
+++ b/README.md
@@ -142,6 +142,75 @@ final class YourService
 }
 ```
 
+## How it works
+
+Dispatching a `ConversionsApiEventRaised` runs the event through a pipeline of listeners. The bundle populates the
+event first, then leaves a gap for your own listeners, then filters and sends:
+
+| Priority                              | Listener                                          | What it does                                            |
+|---------------------------------------|---------------------------------------------------|---------------------------------------------------------|
+| `PRIORITY_POPULATE` (1000)            | `PopulateRequestPropertiesSubscriber`             | Source url, client ip and user agent from the request   |
+| 900                                   | `PopulateFbpAndFbcPropertiesSubscriber`           | `fbp` and `fbc`                                         |
+| 800                                   | `PopulateTestEventCodePropertySubscriber`         | Test event code                                         |
+| 700                                   | `PopulatePixelsSubscriber`                        | Pixels from the pixel provider                          |
+| **`PRIORITY_ENRICH` (0)**             | **your listeners**                                | **Email, phone, external id, custom data**              |
+| -850                                  | `FilterEmptyUserAgentSubscriber`                  | Stops events without a user agent                       |
+| -875                                  | `FilterConfiguredUserAgentsSubscriber`            | Stops events matching `filters.user_agent`              |
+| `PRIORITY_FILTER` (-900)              | `FilterBotsSubscriber`                            | Stops events from bots                                  |
+| -950                                  | `StopPropagationIfNoPixelsHasBeenAddedSubscriber` | Stops events without pixels                             |
+| `PRIORITY_SEND` (-1000)               | `AddEventToTagBagSubscriber`                      | Renders the `fbq()` calls (client side)                 |
+| `PRIORITY_SEND` (-1000)               | `DispatchOnCommandBusSubscriber`                  | Dispatches `SendEvent` (server side)                    |
+
+Two things follow from this:
+
+- **Enrich at `PRIORITY_ENRICH`**, which is the default priority of any listener. Everything the bundle knows about
+  the request is populated by then, and nothing has been filtered or sent yet.
+- **A listener below `PRIORITY_FILTER` may never run**, because the filters stop propagation.
+
+The constants live on `ConversionsApiEventRaised`, so you can position your listener without hard coding a number.
+
+### Enriching an event
+
+Everything the Conversions API can do beyond the browser pixel comes from the user data you attach server side. Meta
+normalises and hashes it for you, so set the raw values:
+
+```php
+<?php
+
+declare(strict_types=1);
+
+namespace App\EventListener;
+
+use Setono\MetaConversionsApiBundle\Event\ConversionsApiEventRaised;
+use Symfony\Bundle\SecurityBundle\Security;
+use Symfony\Component\EventDispatcher\Attribute\AsEventListener;
+
+#[AsEventListener(priority: ConversionsApiEventRaised::PRIORITY_ENRICH)]
+final class AddCustomerToConversionsApiEvent
+{
+    public function __construct(private readonly Security $security)
+    {
+    }
+
+    public function __invoke(ConversionsApiEventRaised $event): void
+    {
+        $user = $this->security->getUser();
+        if (!$user instanceof User) {
+            return;
+        }
+
+        $userData = $event->event->userData;
+        $userData->email[] = $user->getEmail();
+        $userData->firstName[] = $user->getFirstName();
+        $userData->lastName[] = $user->getLastName();
+        $userData->externalId[] = (string) $user->getId();
+    }
+}
+```
+
+You can also replace a step instead of adding to it: alias `PixelProviderInterface`, `FbpContextInterface` or
+`FbcContextInterface` to your own service, or register a listener above the corresponding populate priority.
+
 ## Graph API version
 
 Events are posted to the Graph API version of the installed `facebook/php-business-sdk` package (the SDK reads
diff --git a/src/Event/ConversionsApiEventRaised.php b/src/Event/ConversionsApiEventRaised.php
index 3489281..b5a8f0a 100644
--- a/src/Event/ConversionsApiEventRaised.php
+++ b/src/Event/ConversionsApiEventRaised.php
@@ -9,9 +9,42 @@
 
 /**
  * Dispatch this event onto the EventDispatcher and everything will be handled for you
+ *
+ * The bundle's own listeners run in four bands. Use the constants below to position your own listener relative to
+ * them instead of hard coding a number:
+ *
+ * | Priority                       | What happens                                                          |
+ * |--------------------------------|-----------------------------------------------------------------------|
+ * | PRIORITY_POPULATE (and below)  | The bundle fills in request properties, fbp/fbc, test event code, pixels |
+ * | PRIORITY_ENRICH                | Your listeners add user data and custom data                          |
+ * | PRIORITY_FILTER                | The bundle drops events it should not track (bots, filtered user agents) |
+ * | PRIORITY_SEND                  | The bundle renders the client side tags and dispatches the command      |
+ *
+ * A listener below PRIORITY_FILTER may never run, because the filters stop propagation
  */
 final class ConversionsApiEventRaised extends StoppableEvent
 {
+    /**
+     * The bundle populates the event from the current request at this priority and just below it
+     */
+    public const PRIORITY_POPULATE = 1000;
+
+    /**
+     * The priority your own listeners should use. Everything the bundle knows about the request is populated by
+     * now, and nothing has been filtered or sent yet. This is the default priority of an event listener
+     */
+    public const PRIORITY_ENRICH = 0;
+
+    /**
+     * The bundle decides here whether the event should be tracked at all
+     */
+    public const PRIORITY_FILTER = -900;
+
+    /**
+     * The bundle hands the event to the tag bag and the command bus at this priority
+     */
+    public const PRIORITY_SEND = -1000;
+
     /**
      * @param array<string, mixed> $context
      */
diff --git a/src/EventSubscriber/AddEventToTagBagSubscriber.php b/src/EventSubscriber/AddEventToTagBagSubscriber.php
index 14f9589..9394af4 100644
--- a/src/EventSubscriber/AddEventToTagBagSubscriber.php
+++ b/src/EventSubscriber/AddEventToTagBagSubscriber.php
@@ -25,7 +25,7 @@ public function __construct(
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['add', -1000],
+            ConversionsApiEventRaised::class => ['add', ConversionsApiEventRaised::PRIORITY_SEND],
         ];
     }
 
diff --git a/src/EventSubscriber/DispatchOnCommandBusSubscriber.php b/src/EventSubscriber/DispatchOnCommandBusSubscriber.php
index ff79721..e52fe95 100644
--- a/src/EventSubscriber/DispatchOnCommandBusSubscriber.php
+++ b/src/EventSubscriber/DispatchOnCommandBusSubscriber.php
@@ -21,7 +21,7 @@ public function __construct(
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['dispatch', -1000],
+            ConversionsApiEventRaised::class => ['dispatch', ConversionsApiEventRaised::PRIORITY_SEND],
         ];
     }
 
diff --git a/src/EventSubscriber/FilterBotsSubscriber.php b/src/EventSubscriber/FilterBotsSubscriber.php
index ff35c26..a407055 100644
--- a/src/EventSubscriber/FilterBotsSubscriber.php
+++ b/src/EventSubscriber/FilterBotsSubscriber.php
@@ -17,7 +17,7 @@ public function __construct(private readonly BotDetectorInterface $botDetector)
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['filter', -900],
+            ConversionsApiEventRaised::class => ['filter', ConversionsApiEventRaised::PRIORITY_FILTER],
         ];
     }
 
diff --git a/src/EventSubscriber/FilterConfiguredUserAgentsSubscriber.php b/src/EventSubscriber/FilterConfiguredUserAgentsSubscriber.php
index 6ba48b2..4ce047c 100644
--- a/src/EventSubscriber/FilterConfiguredUserAgentsSubscriber.php
+++ b/src/EventSubscriber/FilterConfiguredUserAgentsSubscriber.php
@@ -44,7 +44,7 @@ public function __construct(array $userAgents)
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['filter', -875],
+            ConversionsApiEventRaised::class => ['filter', ConversionsApiEventRaised::PRIORITY_FILTER + 25],
         ];
     }
 
diff --git a/src/EventSubscriber/FilterEmptyUserAgentSubscriber.php b/src/EventSubscriber/FilterEmptyUserAgentSubscriber.php
index 834cfa4..7abec51 100644
--- a/src/EventSubscriber/FilterEmptyUserAgentSubscriber.php
+++ b/src/EventSubscriber/FilterEmptyUserAgentSubscriber.php
@@ -12,7 +12,7 @@ final class FilterEmptyUserAgentSubscriber implements EventSubscriberInterface
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['filter', -850],
+            ConversionsApiEventRaised::class => ['filter', ConversionsApiEventRaised::PRIORITY_FILTER + 50],
         ];
     }
 
diff --git a/src/EventSubscriber/PopulateFbpAndFbcPropertiesSubscriber.php b/src/EventSubscriber/PopulateFbpAndFbcPropertiesSubscriber.php
index 11886df..11de20e 100644
--- a/src/EventSubscriber/PopulateFbpAndFbcPropertiesSubscriber.php
+++ b/src/EventSubscriber/PopulateFbpAndFbcPropertiesSubscriber.php
@@ -20,7 +20,7 @@ public function __construct(
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['populate', 900],
+            ConversionsApiEventRaised::class => ['populate', ConversionsApiEventRaised::PRIORITY_POPULATE - 100],
         ];
     }
 
diff --git a/src/EventSubscriber/PopulatePixelsSubscriber.php b/src/EventSubscriber/PopulatePixelsSubscriber.php
index b71bbba..f55c1b0 100644
--- a/src/EventSubscriber/PopulatePixelsSubscriber.php
+++ b/src/EventSubscriber/PopulatePixelsSubscriber.php
@@ -17,7 +17,7 @@ public function __construct(private readonly PixelProviderInterface $pixelProvid
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['populate', 700],
+            ConversionsApiEventRaised::class => ['populate', ConversionsApiEventRaised::PRIORITY_POPULATE - 300],
         ];
     }
 
diff --git a/src/EventSubscriber/PopulateRequestPropertiesSubscriber.php b/src/EventSubscriber/PopulateRequestPropertiesSubscriber.php
index 3f07711..afb22b3 100644
--- a/src/EventSubscriber/PopulateRequestPropertiesSubscriber.php
+++ b/src/EventSubscriber/PopulateRequestPropertiesSubscriber.php
@@ -17,7 +17,7 @@ public function __construct(private readonly RequestStack $requestStack)
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['populate', 1000],
+            ConversionsApiEventRaised::class => ['populate', ConversionsApiEventRaised::PRIORITY_POPULATE],
         ];
     }
 
diff --git a/src/EventSubscriber/PopulateTestEventCodePropertySubscriber.php b/src/EventSubscriber/PopulateTestEventCodePropertySubscriber.php
index 5770ece..802dbb5 100644
--- a/src/EventSubscriber/PopulateTestEventCodePropertySubscriber.php
+++ b/src/EventSubscriber/PopulateTestEventCodePropertySubscriber.php
@@ -23,7 +23,7 @@ public function __construct(
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['populate', 800],
+            ConversionsApiEventRaised::class => ['populate', ConversionsApiEventRaised::PRIORITY_POPULATE - 200],
         ];
     }
 
diff --git a/src/EventSubscriber/StopPropagationIfNoPixelsHasBeenAddedSubscriber.php b/src/EventSubscriber/StopPropagationIfNoPixelsHasBeenAddedSubscriber.php
index 5331399..d111744 100644
--- a/src/EventSubscriber/StopPropagationIfNoPixelsHasBeenAddedSubscriber.php
+++ b/src/EventSubscriber/StopPropagationIfNoPixelsHasBeenAddedSubscriber.php
@@ -12,7 +12,7 @@ final class StopPropagationIfNoPixelsHasBeenAddedSubscriber implements EventSubs
     public static function getSubscribedEvents(): array
     {
         return [
-            ConversionsApiEventRaised::class => ['filter', -950],
+            ConversionsApiEventRaised::class => ['filter', ConversionsApiEventRaised::PRIORITY_SEND + 50],
         ];
     }
 
diff --git a/tests/Unit/Event/ConversionsApiEventRaisedTest.php b/tests/Unit/Event/ConversionsApiEventRaisedTest.php
new file mode 100644
index 0000000..a56624d
--- /dev/null
+++ b/tests/Unit/Event/ConversionsApiEventRaisedTest.php
@@ -0,0 +1,122 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Setono\MetaConversionsApiBundle\Tests\Unit\Event;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Test;
+use PHPUnit\Framework\TestCase;
+use Setono\MetaConversionsApi\Event\Event;
+use Setono\MetaConversionsApiBundle\Event\ConversionsApiEventRaised;
+use Setono\MetaConversionsApiBundle\EventSubscriber\AddEventToTagBagSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\DispatchOnCommandBusSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\FilterBotsSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\FilterConfiguredUserAgentsSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\FilterEmptyUserAgentSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\PopulateFbpAndFbcPropertiesSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\PopulatePixelsSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\PopulateRequestPropertiesSubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\PopulateTestEventCodePropertySubscriber;
+use Setono\MetaConversionsApiBundle\EventSubscriber\StopPropagationIfNoPixelsHasBeenAddedSubscriber;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+#[CoversClass(ConversionsApiEventRaised::class)]
+final class ConversionsApiEventRaisedTest extends TestCase
+{
+    /**
+     * The subscribers the bundle registers, in the order the event dispatcher must call them
+     *
+     * @var list<class-string<EventSubscriberInterface>>
+     */
+    private const PIPELINE = [
+        PopulateRequestPropertiesSubscriber::class,
+        PopulateFbpAndFbcPropertiesSubscriber::class,
+        PopulateTestEventCodePropertySubscriber::class,
+        PopulatePixelsSubscriber::class,
+        FilterEmptyUserAgentSubscriber::class,
+        FilterConfiguredUserAgentsSubscriber::class,
+        FilterBotsSubscriber::class,
+        StopPropagationIfNoPixelsHasBeenAddedSubscriber::class,
+        AddEventToTagBagSubscriber::class,
+        DispatchOnCommandBusSubscriber::class,
+    ];
+
+    #[Test]
+    public function it_has_context(): void
+    {
+        $event = new ConversionsApiEventRaised(new Event(Event::EVENT_VIEW_CONTENT), ['order' => 1]);
+
+        self::assertTrue($event->hasContext('order'));
+        self::assertFalse($event->hasContext('customer'));
+    }
+
+    /**
+     * The documented pipeline only holds as long as the bundle's own listeners keep their relative order, so this
+     * pins it down. It is the contract integrators position their own listeners against
+     */
+    #[Test]
+    public function the_pipeline_runs_in_the_documented_order(): void
+    {
+        $previous = null;
+
+        foreach (self::PIPELINE as $subscriber) {
+            $priority = self::priority($subscriber);
+
+            if (null !== $previous) {
+                self::assertLessThanOrEqual($previous, $priority, sprintf('%s runs out of order', $subscriber));
+            }
+
+            $previous = $priority;
+        }
+    }
+
+    #[Test]
+    public function everything_is_populated_before_your_listeners_run(): void
+    {
+        foreach ([
+            PopulateRequestPropertiesSubscriber::class,
+            PopulateFbpAndFbcPropertiesSubscriber::class,
+            PopulateTestEventCodePropertySubscriber::class,
+            PopulatePixelsSubscriber::class,
+        ] as $subscriber) {
+            self::assertGreaterThan(ConversionsApiEventRaised::PRIORITY_ENRICH, self::priority($subscriber));
+        }
+    }
+
+    #[Test]
+    public function filtering_and_sending_happen_after_your_listeners(): void
+    {
+        foreach ([
+            FilterEmptyUserAgentSubscriber::class,
+            FilterConfiguredUserAgentsSubscriber::class,
+            FilterBotsSubscriber::class,
+            StopPropagationIfNoPixelsHasBeenAddedSubscriber::class,
+            AddEventToTagBagSubscriber::class,
+            DispatchOnCommandBusSubscriber::class,
+        ] as $subscriber) {
+            self::assertLessThan(ConversionsApiEventRaised::PRIORITY_ENRICH, self::priority($subscriber));
+        }
+    }
+
+    #[Test]
+    public function the_sinks_run_last(): void
+    {
+        self::assertSame(ConversionsApiEventRaised::PRIORITY_SEND, self::priority(AddEventToTagBagSubscriber::class));
+        self::assertSame(ConversionsApiEventRaised::PRIORITY_SEND, self::priority(DispatchOnCommandBusSubscriber::class));
+    }
+
+    /**
+     * @param class-string<EventSubscriberInterface> $subscriber
+     */
+    private static function priority(string $subscriber): int
+    {
+        $listener = $subscriber::getSubscribedEvents()[ConversionsApiEventRaised::class] ?? null;
+
+        self::assertIsArray($listener);
+        self::assertArrayHasKey(1, $listener);
+        self::assertIsInt($listener[1]);
+
+        return $listener[1];
+    }
+}