--- /dev/null
+<?php
+
+namespace Drupal\video_embed_field\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Validation constraint for the video embed field.
+ *
+ * @Constraint(
+ * id = "VideoEmbedValidation",
+ * label = @Translation("VideoEmbed provider constraint", context = "Validation"),
+ * )
+ */
+class VideoEmbedConstraint extends Constraint {
+
+ /**
+ * Message shown when a video provider is not found.
+ *
+ * @var string
+ */
+ public $message = 'Could not find a video provider to handle the given URL.';
+
+}