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
@@ -285,7 +285,7 @@
     'ConpherenceSettings' => 'applications/conpherence/constants/ConpherenceSettings.php',
     'ConpherenceTestCase' => 'applications/conpherence/__tests__/ConpherenceTestCase.php',
     'ConpherenceThread' => 'applications/conpherence/storage/ConpherenceThread.php',
-    'ConpherenceThreadIndexer' => 'applications/conpherence/search/ConpherenceThreadIndexer.php',
+    'ConpherenceThreadIndexEngineExtension' => 'applications/conpherence/engineextension/ConpherenceThreadIndexEngineExtension.php',
     'ConpherenceThreadListView' => 'applications/conpherence/view/ConpherenceThreadListView.php',
     'ConpherenceThreadMailReceiver' => 'applications/conpherence/mail/ConpherenceThreadMailReceiver.php',
     'ConpherenceThreadMembersPolicyRule' => 'applications/conpherence/policyrule/ConpherenceThreadMembersPolicyRule.php',
@@ -2378,6 +2378,8 @@
     'PhabricatorImageTransformer' => 'applications/files/PhabricatorImageTransformer.php',
     'PhabricatorImagemagickSetupCheck' => 'applications/config/check/PhabricatorImagemagickSetupCheck.php',
     'PhabricatorIndexEngine' => 'applications/search/index/PhabricatorIndexEngine.php',
+    'PhabricatorIndexEngineExtension' => 'applications/search/index/PhabricatorIndexEngineExtension.php',
+    'PhabricatorIndexEngineExtensionModule' => 'applications/search/index/PhabricatorIndexEngineExtensionModule.php',
     'PhabricatorInfrastructureTestCase' => '__tests__/PhabricatorInfrastructureTestCase.php',
     'PhabricatorInlineCommentController' => 'infrastructure/diff/PhabricatorInlineCommentController.php',
     'PhabricatorInlineCommentInterface' => 'infrastructure/diff/interface/PhabricatorInlineCommentInterface.php',
@@ -4181,7 +4183,7 @@
       'PhabricatorMentionableInterface',
       'PhabricatorDestructibleInterface',
     ),
-    'ConpherenceThreadIndexer' => 'PhabricatorSearchDocumentIndexer',
+    'ConpherenceThreadIndexEngineExtension' => 'PhabricatorIndexEngineExtension',
     'ConpherenceThreadListView' => 'AphrontView',
     'ConpherenceThreadMailReceiver' => 'PhabricatorObjectMailReceiver',
     'ConpherenceThreadMembersPolicyRule' => 'PhabricatorPolicyRule',
@@ -6606,6 +6608,8 @@
     'PhabricatorImageTransformer' => 'Phobject',
     'PhabricatorImagemagickSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorIndexEngine' => 'Phobject',
+    'PhabricatorIndexEngineExtension' => 'Phobject',
+    'PhabricatorIndexEngineExtensionModule' => 'PhabricatorConfigModule',
     'PhabricatorInfrastructureTestCase' => 'PhabricatorTestCase',
     'PhabricatorInlineCommentController' => 'PhabricatorController',
     'PhabricatorInlineCommentInterface' => 'PhabricatorMarkupInterface',
diff --git a/src/applications/conpherence/editor/ConpherenceEditor.php b/src/applications/conpherence/editor/ConpherenceEditor.php
--- a/src/applications/conpherence/editor/ConpherenceEditor.php
+++ b/src/applications/conpherence/editor/ConpherenceEditor.php
@@ -601,22 +601,6 @@
     return true;
   }
 
-  protected function getSearchContextParameter(
-    PhabricatorLiskDAO $object,
-    array $xactions) {
-
-    $comment_phids = array();
-    foreach ($xactions as $xaction) {
-      if ($xaction->hasComment()) {
-        $comment_phids[] = $xaction->getPHID();
-      }
-    }
-
-    return array(
-      'commentPHIDs' => $comment_phids,
-    );
-  }
-
   protected function extractFilePHIDsFromCustomTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
diff --git a/src/applications/conpherence/search/ConpherenceThreadIndexer.php b/src/applications/conpherence/engineextension/ConpherenceThreadIndexEngineExtension.php
rename from src/applications/conpherence/search/ConpherenceThreadIndexer.php
rename to src/applications/conpherence/engineextension/ConpherenceThreadIndexEngineExtension.php
--- a/src/applications/conpherence/search/ConpherenceThreadIndexer.php
+++ b/src/applications/conpherence/engineextension/ConpherenceThreadIndexEngineExtension.php
@@ -1,58 +1,50 @@
 <?php
 
-final class ConpherenceThreadIndexer
-  extends PhabricatorSearchDocumentIndexer {
+final class ConpherenceThreadIndexEngineExtension
+  extends PhabricatorIndexEngineExtension {
 
-  public function getIndexableObject() {
-    return new ConpherenceThread();
-  }
-
-  protected function loadDocumentByPHID($phid) {
-    $object = id(new ConpherenceThreadQuery())
-      ->setViewer($this->getViewer())
-      ->withPHIDs(array($phid))
-      ->executeOne();
-
-    if (!$object) {
-      throw new Exception(pht('No thread "%s" exists!', $phid));
-    }
+  const EXTENSIONKEY = 'conpherence.thread';
 
-    return $object;
+  public function getExtensionName() {
+    return pht('Conpherence Threads');
   }
 
-  protected function buildAbstractDocumentByPHID($phid) {
-    $thread = $this->loadDocumentByPHID($phid);
+  public function shouldIndexObject($object) {
+    return ($object instanceof ConpherenceThread);
+  }
 
-    // NOTE: We're explicitly not building a document here, only rebuilding
-    // the Conpherence search index.
+  public function indexObject(
+    PhabricatorIndexEngine $engine,
+    $object) {
 
-    $context = nonempty($this->getContext(), array());
-    $comment_phids = idx($context, 'commentPHIDs');
+    $force = $this->shouldForceFullReindex();
 
-    if (is_array($comment_phids) && !$comment_phids) {
-      // If this property is set, but empty, the transaction did not
-      // include any chat text. For example, a user might have left the
-      // conversation.
-      return null;
+    if (!$force) {
+      $xaction_phids = $this->getParameter('transactionPHIDs');
+      if (!$xaction_phids) {
+        return;
+      }
     }
 
     $query = id(new ConpherenceTransactionQuery())
       ->setViewer($this->getViewer())
-      ->withObjectPHIDs(array($thread->getPHID()))
+      ->withObjectPHIDs(array($object->getPHID()))
       ->withTransactionTypes(array(PhabricatorTransactions::TYPE_COMMENT))
       ->needComments(true);
 
-    if ($comment_phids !== null) {
-      $query->withPHIDs($comment_phids);
+    if (!$force) {
+      $query->withPHIDs($xaction_phids);
     }
 
     $xactions = $query->execute();
 
-    foreach ($xactions as $xaction) {
-      $this->indexComment($thread, $xaction);
+    if (!$xactions) {
+      return;
     }
 
-    return null;
+    foreach ($xactions as $xaction) {
+      $this->indexComment($object, $xaction);
+    }
   }
 
   private function indexComment(
diff --git a/src/applications/search/index/PhabricatorIndexEngine.php b/src/applications/search/index/PhabricatorIndexEngine.php
--- a/src/applications/search/index/PhabricatorIndexEngine.php
+++ b/src/applications/search/index/PhabricatorIndexEngine.php
@@ -2,14 +2,108 @@
 
 final class PhabricatorIndexEngine extends Phobject {
 
-  public function indexDocumentByPHID($phid, $context) {
+  private $object;
+  private $extensions;
+  private $versions;
+  private $parameters;
+
+  public function setParameters(array $parameters) {
+    $this->parameters = $parameters;
+    return $this;
+  }
+
+  public function getParameters() {
+    return $this->parameters;
+  }
+
+  public function setObject($object) {
+    $this->object = $object;
+    return $this;
+  }
+
+  public function getObject() {
+    return $this->object;
+  }
+
+  public function shouldIndexObject() {
+    $extensions = $this->newExtensions();
+
+    $parameters = $this->getParameters();
+    foreach ($extensions as $extension) {
+      $extension->setParameters($parameters);
+    }
+
+    $object = $this->getObject();
+    $versions = array();
+    foreach ($extensions as $key => $extension) {
+      $version = $extension->getIndexVersion($object);
+      if ($version !== null) {
+        $versions[$key] = (string)$version;
+      }
+    }
+
+    if (idx($parameters, 'force')) {
+      $current_versions = array();
+    } else {
+      // TODO: Load current indexed versions.
+      $current_versions = array();
+    }
+
+    foreach ($versions as $key => $version) {
+      $current_version = idx($current_versions, $key);
+
+      if ($current_version === null) {
+        continue;
+      }
+
+      // If nothing has changed since we built the current index, we do not
+      // need to rebuild the index.
+      if ($current_version === $version) {
+        unset($extensions[$key]);
+      }
+    }
+
+    $this->extensions = $extensions;
+    $this->versions = $versions;
+
+    // We should index the object only if there is any work to be done.
+    return (bool)$this->extensions;
+  }
+
+  public function indexObject() {
+    $extensions = $this->extensions;
+    $object = $this->getObject();
+
+    foreach ($extensions as $key => $extension) {
+      $extension->indexObject($this, $object);
+    }
+
+    // TODO: Save new index versions.
+
+    return $this;
+  }
+
+  private function newExtensions() {
+    $object = $this->getObject();
+
+    $extensions = PhabricatorIndexEngineExtension::getAllExtensions();
+    foreach ($extensions as $key => $extension) {
+      if (!$extension->shouldIndexObject($object)) {
+        unset($extensions[$key]);
+      }
+    }
+
+    return $extensions;
+  }
+
+  public function indexDocumentByPHID($phid) {
     $indexers = id(new PhutilClassMapQuery())
       ->setAncestorClass('PhabricatorSearchDocumentIndexer')
       ->execute();
 
     foreach ($indexers as $indexer) {
       if ($indexer->shouldIndexDocumentByPHID($phid)) {
-        $indexer->indexDocumentByPHID($phid, $context);
+        $indexer->indexDocumentByPHID($phid);
         break;
       }
     }
diff --git a/src/applications/search/index/PhabricatorIndexEngineExtension.php b/src/applications/search/index/PhabricatorIndexEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/search/index/PhabricatorIndexEngineExtension.php
@@ -0,0 +1,48 @@
+<?php
+
+abstract class PhabricatorIndexEngineExtension extends Phobject {
+
+  private $parameters;
+  private $forceFullReindex;
+
+  public function setParameters(array $parameters) {
+    $this->parameters = $parameters;
+    return $this;
+  }
+
+  public function getParameter($key, $default = null) {
+    return idx($this->parameters, $key, $default);
+  }
+
+  final public function getExtensionKey() {
+    return $this->getPhobjectClassConstant('EXTENSIONKEY');
+  }
+
+  final protected function getViewer() {
+    return PhabricatorUser::getOmnipotentUser();
+  }
+
+  abstract public function getExtensionName();
+
+  abstract public function shouldIndexObject($object);
+
+  abstract public function indexObject(
+    PhabricatorIndexEngine $engine,
+    $object);
+
+  public function getIndexVersion($object) {
+    return null;
+  }
+
+  final public static function getAllExtensions() {
+    return id(new PhutilClassMapQuery())
+      ->setAncestorClass(__CLASS__)
+      ->setUniqueMethod('getExtensionKey')
+      ->execute();
+  }
+
+  final public function shouldForceFullReindex() {
+    return $this->getParameter('force');
+  }
+
+}
diff --git a/src/applications/search/index/PhabricatorIndexEngineExtensionModule.php b/src/applications/search/index/PhabricatorIndexEngineExtensionModule.php
new file mode 100644
--- /dev/null
+++ b/src/applications/search/index/PhabricatorIndexEngineExtensionModule.php
@@ -0,0 +1,44 @@
+<?php
+
+final class PhabricatorIndexEngineExtensionModule
+  extends PhabricatorConfigModule {
+
+  public function getModuleKey() {
+    return 'indexengine';
+  }
+
+  public function getModuleName() {
+    return pht('Engine: Index');
+  }
+
+  public function renderModuleStatus(AphrontRequest $request) {
+    $viewer = $request->getViewer();
+
+    $extensions = PhabricatorIndexEngineExtension::getAllExtensions();
+
+    $rows = array();
+    foreach ($extensions as $extension) {
+      $rows[] = array(
+        get_class($extension),
+        $extension->getExtensionName(),
+      );
+    }
+
+    $table = id(new AphrontTableView($rows))
+      ->setHeaders(
+        array(
+          pht('Class'),
+          pht('Name'),
+        ))
+      ->setColumnClasses(
+        array(
+          null,
+          'wide pri',
+        ));
+
+    return id(new PHUIObjectBoxView())
+      ->setHeaderText(pht('IndexEngine Extensions'))
+      ->setTable($table);
+  }
+
+}
diff --git a/src/applications/search/index/PhabricatorSearchDocumentIndexer.php b/src/applications/search/index/PhabricatorSearchDocumentIndexer.php
--- a/src/applications/search/index/PhabricatorSearchDocumentIndexer.php
+++ b/src/applications/search/index/PhabricatorSearchDocumentIndexer.php
@@ -2,17 +2,6 @@
 
 abstract class PhabricatorSearchDocumentIndexer extends Phobject {
 
-  private $context;
-
-  protected function setContext($context) {
-    $this->context = $context;
-    return $this;
-  }
-
-  protected function getContext() {
-    return $this->context;
-  }
-
   abstract public function getIndexableObject();
   abstract protected function buildAbstractDocumentByPHID($phid);
 
@@ -41,9 +30,7 @@
     return $object;
   }
 
-  public function indexDocumentByPHID($phid, $context) {
-    $this->setContext($context);
-
+  public function indexDocumentByPHID($phid) {
     $document = $this->buildAbstractDocumentByPHID($phid);
     if ($document === null) {
       // This indexer doesn't build a document index, so we're done.
diff --git a/src/applications/search/management/PhabricatorSearchManagementIndexWorkflow.php b/src/applications/search/management/PhabricatorSearchManagementIndexWorkflow.php
--- a/src/applications/search/management/PhabricatorSearchManagementIndexWorkflow.php
+++ b/src/applications/search/management/PhabricatorSearchManagementIndexWorkflow.php
@@ -30,6 +30,13 @@
               'it more difficult to debug search indexing.'),
           ),
           array(
+            'name' => 'force',
+            'short' => 'f',
+            'help' => pht(
+              'Force a complete rebuild of the entire index instead of an '.
+              'incremental update.'),
+          ),
+          array(
             'name'      => 'objects',
             'wildcard'  => true,
           ),
@@ -41,6 +48,7 @@
 
     $is_all = $args->getArg('all');
     $is_type = $args->getArg('type');
+    $is_force = $args->getArg('force');
 
     $obj_names = $args->getArg('objects');
 
@@ -93,10 +101,14 @@
     $bar = id(new PhutilConsoleProgressBar())
       ->setTotal(count($phids));
 
+    $parameters = array(
+      'force' => $is_force,
+    );
+
     $any_success = false;
     foreach ($phids as $phid) {
       try {
-        PhabricatorSearchWorker::queueDocumentForIndexing($phid);
+        PhabricatorSearchWorker::queueDocumentForIndexing($phid, $parameters);
         $any_success = true;
       } catch (Exception $ex) {
         phlog($ex);
diff --git a/src/applications/search/worker/PhabricatorSearchWorker.php b/src/applications/search/worker/PhabricatorSearchWorker.php
--- a/src/applications/search/worker/PhabricatorSearchWorker.php
+++ b/src/applications/search/worker/PhabricatorSearchWorker.php
@@ -2,12 +2,16 @@
 
 final class PhabricatorSearchWorker extends PhabricatorWorker {
 
-  public static function queueDocumentForIndexing($phid, $context = null) {
+  public static function queueDocumentForIndexing($phid, $parameters = null) {
+    if ($parameters === null) {
+      $parameters = array();
+    }
+
     parent::scheduleTask(
       __CLASS__,
       array(
         'documentPHID' => $phid,
-        'context' => $context,
+        'parameters' => $parameters,
       ),
       array(
         'priority' => parent::PRIORITY_IMPORT,
@@ -17,9 +21,18 @@
   protected function doWork() {
     $data = $this->getTaskData();
     $object_phid = idx($data, 'documentPHID');
-    $context = idx($data, 'context');
 
-    $engine = new PhabricatorIndexEngine();
+    $object = $this->loadObjectForIndexing($object_phid);
+
+    $engine = id(new PhabricatorIndexEngine())
+      ->setObject($object);
+
+    $parameters = idx($data, 'parameters', array());
+    $engine->setParameters($parameters);
+
+    if (!$engine->shouldIndexObject()) {
+      return;
+    }
 
     $key = "index.{$object_phid}";
     $lock = PhabricatorGlobalLock::newLock($key);
@@ -27,10 +40,15 @@
     $lock->lock(1);
 
     try {
-      $object = $this->loadObjectForIndexing($object_phid);
+      // Reload the object now that we have a lock, to make sure we have the
+      // most current version.
+      $object = $this->loadObjectForIndexing($object->getPHID());
+
+      $engine->setObject($object);
 
-      $engine->indexDocumentByPHID($object->getPHID(), $context);
+      $engine->indexObject();
 
+      $engine->indexDocumentByPHID($object->getPHID());
     } catch (Exception $ex) {
       $lock->unlock();
 
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
@@ -1095,7 +1095,9 @@
     if ($this->supportsSearch()) {
       PhabricatorSearchWorker::queueDocumentForIndexing(
         $object->getPHID(),
-        $this->getSearchContextParameter($object, $xactions));
+        array(
+          'transactionPHIDs' => mpull($xactions, 'getPHID'),
+        ));
     }
 
     if ($this->shouldPublishFeedStory($object, $xactions)) {
@@ -2862,15 +2864,6 @@
     return false;
   }
 
-  /**
-   * @task search
-   */
-  protected function getSearchContextParameter(
-    PhabricatorLiskDAO $object,
-    array $xactions) {
-    return null;
-  }
-
 
 /* -(  Herald Integration )-------------------------------------------------- */