diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3061,6 +3061,8 @@
     'PhabricatorEditPage' => 'applications/transactions/editengine/PhabricatorEditPage.php',
     'PhabricatorEditType' => 'applications/transactions/edittype/PhabricatorEditType.php',
     'PhabricatorEditor' => 'infrastructure/PhabricatorEditor.php',
+    'PhabricatorEditorExtension' => 'applications/transactions/engineextension/PhabricatorEditorExtension.php',
+    'PhabricatorEditorExtensionModule' => 'applications/transactions/engineextension/PhabricatorEditorExtensionModule.php',
     'PhabricatorEditorMailEngineExtension' => 'applications/transactions/engineextension/PhabricatorEditorMailEngineExtension.php',
     'PhabricatorEditorMultipleSetting' => 'applications/settings/setting/PhabricatorEditorMultipleSetting.php',
     'PhabricatorEditorSetting' => 'applications/settings/setting/PhabricatorEditorSetting.php',
@@ -8927,6 +8929,8 @@
     'PhabricatorEditPage' => 'Phobject',
     'PhabricatorEditType' => 'Phobject',
     'PhabricatorEditor' => 'Phobject',
+    'PhabricatorEditorExtension' => 'Phobject',
+    'PhabricatorEditorExtensionModule' => 'PhabricatorConfigModule',
     'PhabricatorEditorMailEngineExtension' => 'PhabricatorMailEngineExtension',
     'PhabricatorEditorMultipleSetting' => 'PhabricatorSelectSetting',
     'PhabricatorEditorSetting' => 'PhabricatorStringSetting',
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -88,6 +88,7 @@
   private $hasRequiredMFA = false;
   private $request;
   private $cancelURI;
+  private $extensions;
 
   const STORAGE_ENCODING_BINARY = 'binary';
 
@@ -1013,6 +1014,7 @@
       }
 
       $errors[] = $this->validateAllTransactions($object, $xactions);
+      $errors[] = $this->validateTransactionsWithExtensions($object, $xactions);
       $errors = array_mergev($errors);
 
       $continue_on_missing = $this->getContinueOnMissingFields();
@@ -4975,4 +4977,60 @@
     return $xactions;
   }
 
+
+/* -(  Extensions  )--------------------------------------------------------- */
+
+
+  private function validateTransactionsWithExtensions(
+    PhabricatorLiskDAO $object,
+    array $xactions) {
+    $errors = array();
+
+    $extensions = $this->getEditorExtensions();
+    foreach ($extensions as $extension) {
+      $extension_errors = $extension
+        ->setObject($object)
+        ->validateTransactions($object, $xactions);
+
+      assert_instances_of(
+        $extension_errors,
+        'PhabricatorApplicationTransactionValidationError');
+
+      $errors[] = $extension_errors;
+    }
+
+    return array_mergev($errors);
+  }
+
+  private function getEditorExtensions() {
+    if ($this->extensions === null) {
+      $this->extensions = $this->newEditorExtensions();
+    }
+    return $this->extensions;
+  }
+
+  private function newEditorExtensions() {
+    $extensions = PhabricatorEditorExtension::getAllExtensions();
+
+    $actor = $this->getActor();
+    $object = $this->object;
+    foreach ($extensions as $key => $extension) {
+
+      $extension = id(clone $extension)
+        ->setViewer($actor)
+        ->setEditor($this)
+        ->setObject($object);
+
+      if (!$extension->supportsObject($this, $object)) {
+        unset($extensions[$key]);
+        continue;
+      }
+
+      $extensions[$key] = $extension;
+    }
+
+    return $extensions;
+  }
+
+
 }
diff --git a/src/applications/transactions/engineextension/PhabricatorEditorExtension.php b/src/applications/transactions/engineextension/PhabricatorEditorExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/engineextension/PhabricatorEditorExtension.php
@@ -0,0 +1,83 @@
+<?php
+
+abstract class PhabricatorEditorExtension
+  extends Phobject {
+
+  private $viewer;
+  private $editor;
+  private $object;
+
+  final public function getExtensionKey() {
+    return $this->getPhobjectClassConstant('EXTENSIONKEY');
+  }
+
+  final public function setEditor(
+    PhabricatorApplicationTransactionEditor $editor) {
+    $this->editor = $editor;
+    return $this;
+  }
+
+  final public function getEditor() {
+    return $this->editor;
+  }
+
+  final public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  final public function getViewer() {
+    return $this->viewer;
+  }
+
+  final public function setObject(
+    PhabricatorApplicationTransactionInterface $object) {
+    $this->object = $object;
+    return $this;
+  }
+
+  final public static function getAllExtensions() {
+    return id(new PhutilClassMapQuery())
+      ->setAncestorClass(__CLASS__)
+      ->setUniqueMethod('getExtensionKey')
+      ->execute();
+  }
+
+  abstract public function getExtensionName();
+
+  public function supportsObject(
+    PhabricatorApplicationTransactionEditor $editor,
+    PhabricatorApplicationTransactionInterface $object) {
+    return true;
+  }
+
+  public function validateTransactions($object, array $xactions) {
+    return array();
+  }
+
+  final protected function newTransactionError(
+    PhabricatorApplicationTransaction $xaction,
+    $title,
+    $message) {
+    return new PhabricatorApplicationTransactionValidationError(
+      $xaction->getTransactionType(),
+      $title,
+      $message,
+      $xaction);
+  }
+
+  final protected function newRequiredTransasctionError(
+    PhabricatorApplicationTransaction $xaction,
+    $message) {
+    return $this->newError($xaction, pht('Required'), $message)
+      ->setIsMissingFieldError(true);
+  }
+
+  final protected function newInvalidTransactionError(
+    PhabricatorApplicationTransaction $xaction,
+    $message) {
+    return $this->newTransactionError($xaction, pht('Invalid'), $message);
+  }
+
+
+}
diff --git a/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php b/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php
new file mode 100644
--- /dev/null
+++ b/src/applications/transactions/engineextension/PhabricatorEditorExtensionModule.php
@@ -0,0 +1,40 @@
+<?php
+
+final class PhabricatorEditorExtensionModule
+  extends PhabricatorConfigModule {
+
+  public function getModuleKey() {
+    return 'editor';
+  }
+
+  public function getModuleName() {
+    return pht('Engine: Editor');
+  }
+
+  public function renderModuleStatus(AphrontRequest $request) {
+    $viewer = $request->getViewer();
+
+    $extensions = PhabricatorEditorExtension::getAllExtensions();
+
+    $rows = array();
+    foreach ($extensions as $extension) {
+      $rows[] = array(
+        get_class($extension),
+        $extension->getExtensionName(),
+      );
+    }
+
+    return id(new AphrontTableView($rows))
+      ->setHeaders(
+        array(
+          pht('Class'),
+          pht('Name'),
+        ))
+      ->setColumnClasses(
+        array(
+          null,
+          'wide pri',
+        ));
+  }
+
+}