--- /dev/null
+<?php
+
+namespace Drupal\link\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Defines a protocol validation constraint for links to broken internal URLs.
+ *
+ * @Constraint(
+ * id = "LinkNotExistingInternal",
+ * label = @Translation("No broken internal links", context = "Validation"),
+ * )
+ */
+class LinkNotExistingInternalConstraint extends Constraint {
+
+ public $message = "The path '@uri' is invalid.";
+
+}