diff --git a/src/__celerity_resource_map__.php b/src/__celerity_resource_map__.php
index 5ff960b7ed..44c6321e90 100644
--- a/src/__celerity_resource_map__.php
+++ b/src/__celerity_resource_map__.php
@@ -27,7 +27,7 @@ celerity_register_resource_map(array(
   ),
   'aphront-panel-view-css' =>
   array(
-    'uri' => '/res/fe62e634/rsrc/css/aphront/panel-view.css',
+    'uri' => '/res/63672373/rsrc/css/aphront/panel-view.css',
     'type' => 'css',
     'requires' =>
     array(
@@ -36,7 +36,7 @@ celerity_register_resource_map(array(
   ),
   'aphront-request-failure-view-css' =>
   array(
-    'uri' => '/res/d7df3b42/rsrc/css/aphront/request-failure-view.css',
+    'uri' => '/res/97b8337a/rsrc/css/aphront/request-failure-view.css',
     'type' => 'css',
     'requires' =>
     array(
@@ -89,6 +89,15 @@ celerity_register_resource_map(array(
     ),
     'disk' => '/rsrc/css/application/base/standard-page-view.css',
   ),
+  'differential-revision-add-comment-css' =>
+  array(
+    'uri' => '/res/623fef21/rsrc/css/application/differential/add-comment.css',
+    'type' => 'css',
+    'requires' =>
+    array(
+    ),
+    'disk' => '/rsrc/css/application/differential/add-comment.css',
+  ),
   'differential-changeset-view-css' =>
   array(
     'uri' => '/res/658d181a/rsrc/css/application/differential/changeset-view.css',
@@ -207,6 +216,16 @@ celerity_register_resource_map(array(
     ),
     'disk' => '/rsrc/js/application/core/behavior-tokenizer.js',
   ),
+  'javelin-behavior-differential-feedback-preview' =>
+  array(
+    'uri' => '/res/34fbb670/rsrc/js/application/differential/behavior-comment-preview.js',
+    'type' => 'js',
+    'requires' =>
+    array(
+      0 => 'javelin-lib-dev',
+    ),
+    'disk' => '/rsrc/js/application/differential/behavior-comment-preview.js',
+  ),
   'javelin-behavior-differential-populate' =>
   array(
     'uri' => '/res/9982573c/rsrc/js/application/differential/behavior-populate.js',
@@ -274,7 +293,7 @@ celerity_register_resource_map(array(
 ), array (
   'packages' =>
   array (
-    '364a306c' =>
+    'd348c79d' =>
     array (
       'name' => 'core.pkg.css',
       'symbols' =>
@@ -291,7 +310,7 @@ celerity_register_resource_map(array(
         9 => 'aphront-typeahead-control-css',
         10 => 'phabricator-directory-css',
       ),
-      'uri' => '/res/pkg/364a306c/core.pkg.css',
+      'uri' => '/res/pkg/d348c79d/core.pkg.css',
       'type' => 'css',
     ),
     '69b11588' =>
@@ -311,17 +330,17 @@ celerity_register_resource_map(array(
   ),
   'reverse' =>
   array (
-    'phabricator-core-css' => '364a306c',
-    'phabricator-core-buttons-css' => '364a306c',
-    'phabricator-standard-page-view' => '364a306c',
-    'aphront-dialog-view-css' => '364a306c',
-    'aphront-form-view-css' => '364a306c',
-    'aphront-panel-view-css' => '364a306c',
-    'aphront-side-nav-view-css' => '364a306c',
-    'aphront-table-view-css' => '364a306c',
-    'aphront-tokenizer-control-css' => '364a306c',
-    'aphront-typeahead-control-css' => '364a306c',
-    'phabricator-directory-css' => '364a306c',
+    'phabricator-core-css' => 'd348c79d',
+    'phabricator-core-buttons-css' => 'd348c79d',
+    'phabricator-standard-page-view' => 'd348c79d',
+    'aphront-dialog-view-css' => 'd348c79d',
+    'aphront-form-view-css' => 'd348c79d',
+    'aphront-panel-view-css' => 'd348c79d',
+    'aphront-side-nav-view-css' => 'd348c79d',
+    'aphront-table-view-css' => 'd348c79d',
+    'aphront-tokenizer-control-css' => 'd348c79d',
+    'aphront-typeahead-control-css' => 'd348c79d',
+    'phabricator-directory-css' => 'd348c79d',
     'differential-core-view-css' => '69b11588',
     'differential-changeset-view-css' => '69b11588',
     'differential-revision-detail-css' => '69b11588',
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 261d63ec43..9a5aacd4d4 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -80,6 +80,7 @@ phutil_register_library_map(array(
     'DifferentialComment' => 'applications/differential/storage/comment',
     'DifferentialCommentEditor' => 'applications/differential/editor/comment',
     'DifferentialCommentMail' => 'applications/differential/mail/comment',
+    'DifferentialCommentPreviewController' => 'applications/differential/controller/commentpreview',
     'DifferentialCommentSaveController' => 'applications/differential/controller/commentsave',
     'DifferentialController' => 'applications/differential/controller/base',
     'DifferentialDAO' => 'applications/differential/storage/base',
@@ -253,6 +254,7 @@ phutil_register_library_map(array(
     'DifferentialChangesetViewController' => 'DifferentialController',
     'DifferentialComment' => 'DifferentialDAO',
     'DifferentialCommentMail' => 'DifferentialMail',
+    'DifferentialCommentPreviewController' => 'DifferentialController',
     'DifferentialCommentSaveController' => 'DifferentialController',
     'DifferentialController' => 'PhabricatorController',
     'DifferentialDAO' => 'PhabricatorLiskDAO',
diff --git a/src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php b/src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php
index a7dbbe58cf..046b99f300 100644
--- a/src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php
+++ b/src/aphront/default/configuration/AphrontDefaultApplicationConfiguration.php
@@ -87,7 +87,7 @@ class AphrontDefaultApplicationConfiguration
         'revision/edit/(?:(?<id>\d+)/)?$'
           => 'DifferentialRevisionEditController',
         'comment/' => array(
-          'preview/$' => 'DifferentialCommentPreviewController',
+          'preview/(?<id>\d+)/$' => 'DifferentialCommentPreviewController',
           'save/$' => 'DifferentialCommentSaveController',
           'inline/' => array(
             'preview/$' => 'DifferentialInlineCommentPreviewController',
diff --git a/src/applications/conduit/method/differential/creatediff/__init__.php b/src/applications/conduit/method/differential/creatediff/__init__.php
index f43bd3996d..160deafd17 100644
--- a/src/applications/conduit/method/differential/creatediff/__init__.php
+++ b/src/applications/conduit/method/differential/creatediff/__init__.php
@@ -14,6 +14,7 @@ phutil_require_module('phabricator', 'applications/differential/constants/revisi
 phutil_require_module('phabricator', 'applications/differential/constants/unitstatus');
 phutil_require_module('phabricator', 'applications/differential/storage/diff');
 phutil_require_module('phabricator', 'applications/differential/storage/revision');
+phutil_require_module('phabricator', 'infrastructure/env');
 
 phutil_require_module('phutil', 'utils');
 
diff --git a/src/applications/differential/controller/commentpreview/DifferentialCommentPreviewController.php b/src/applications/differential/controller/commentpreview/DifferentialCommentPreviewController.php
new file mode 100644
index 0000000000..96ef550e44
--- /dev/null
+++ b/src/applications/differential/controller/commentpreview/DifferentialCommentPreviewController.php
@@ -0,0 +1,54 @@
+<?php
+
+/*
+ * Copyright 2011 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+class DifferentialCommentPreviewController extends DifferentialController {
+
+  private $id;
+
+  public function willProcessRequest(array $data) {
+    $this->id = $data['id'];
+  }
+
+  public function processRequest() {
+
+    $request = $this->getRequest();
+
+    $author_phid = $request->getUser()->getPHID();
+
+    $handles = id(new PhabricatorObjectHandleData(array($author_phid)))
+      ->loadHandles();
+
+    $factory = new DifferentialMarkupEngineFactory();
+    $engine = $factory->newDifferentialCommentMarkupEngine();
+
+    $comment = new DifferentialComment();
+    $comment->setContent($request->getStr('content'));
+    $comment->setAction($request->getStr('action'));
+    $comment->setAuthorPHID($author_phid);
+
+    $view = new DifferentialRevisionCommentView();
+    $view->setComment($comment);
+    $view->setHandles($handles);
+    $view->setMarkupEngine($engine);
+    $view->setPreview(true);
+
+    return id(new AphrontAjaxResponse())
+      ->setContent($view->render());
+  }
+
+}
diff --git a/src/applications/differential/controller/commentpreview/__init__.php b/src/applications/differential/controller/commentpreview/__init__.php
new file mode 100644
index 0000000000..0d1ba25e1e
--- /dev/null
+++ b/src/applications/differential/controller/commentpreview/__init__.php
@@ -0,0 +1,19 @@
+<?php
+/**
+ * This file is automatically generated. Lint this module to rebuild it.
+ * @generated
+ */
+
+
+
+phutil_require_module('phabricator', 'aphront/response/ajax');
+phutil_require_module('phabricator', 'applications/differential/controller/base');
+phutil_require_module('phabricator', 'applications/differential/parser/markup');
+phutil_require_module('phabricator', 'applications/differential/storage/comment');
+phutil_require_module('phabricator', 'applications/differential/view/revisioncomment');
+phutil_require_module('phabricator', 'applications/phid/handle/data');
+
+phutil_require_module('phutil', 'utils');
+
+
+phutil_require_source('DifferentialCommentPreviewController.php');
diff --git a/src/applications/differential/mail/base/__init__.php b/src/applications/differential/mail/base/__init__.php
index e37c404c5a..6fa6f9c631 100644
--- a/src/applications/differential/mail/base/__init__.php
+++ b/src/applications/differential/mail/base/__init__.php
@@ -7,6 +7,7 @@
 
 
 phutil_require_module('phabricator', 'applications/metamta/storage/mail');
+phutil_require_module('phabricator', 'infrastructure/env');
 
 
 phutil_require_source('DifferentialMail.php');
diff --git a/src/applications/differential/view/addcomment/DifferentialAddCommentView.php b/src/applications/differential/view/addcomment/DifferentialAddCommentView.php
index b390c5a083..1fc3def9ee 100644
--- a/src/applications/differential/view/addcomment/DifferentialAddCommentView.php
+++ b/src/applications/differential/view/addcomment/DifferentialAddCommentView.php
@@ -42,6 +42,9 @@ final class DifferentialAddCommentView extends AphrontView {
   }
 
   public function render() {
+
+    require_celerity_resource('differential-revision-add-comment-css');
+
     $revision = $this->revision;
 
     $actions = array();
@@ -58,19 +61,39 @@ final class DifferentialAddCommentView extends AphrontView {
         id(new AphrontFormSelectControl())
           ->setLabel('Action')
           ->setName('action')
+          ->setID('comment-action')
           ->setOptions($actions))
       ->appendChild(
         id(new AphrontFormTextAreaControl())
           ->setName('comment')
+          ->setID('comment-content')
           ->setLabel('Comment'))
       ->appendChild(
         id(new AphrontFormSubmitControl())
           ->setValue('Comment'));
 
+    Javelin::initBehavior(
+      'differential-feedback-preview',
+      array(
+        'uri'     => '/differential/comment/preview/'.$revision->getID().'/',
+        'preview' => 'comment-preview',
+        'action'  => 'comment-action',
+        'content' => 'comment-content',
+      ));
+
     return
-      '<div class="differential-panel">'.
-        '<h1>Add Comment</h1>'.
-        $form->render().
+      '<div class="differential-add-comment-panel">'.
+        '<div class="differential-panel">'.
+          '<h1>Add Comment</h1>'.
+          $form->render().
+        '</div>'.
+        '<div class="differential-comment-preview">'.
+          '<div id="comment-preview">'.
+            '<span class="differential-loading-text">'.
+              'Loading comment preview...'.
+            '</span>'.
+          '</div>'.
+        '</div>'.
       '</div>';
   }
 }
diff --git a/src/applications/differential/view/addcomment/__init__.php b/src/applications/differential/view/addcomment/__init__.php
index 67d21d5c5e..1597617bf0 100644
--- a/src/applications/differential/view/addcomment/__init__.php
+++ b/src/applications/differential/view/addcomment/__init__.php
@@ -7,6 +7,8 @@
 
 
 phutil_require_module('phabricator', 'applications/differential/constants/action');
+phutil_require_module('phabricator', 'infrastructure/celerity/api');
+phutil_require_module('phabricator', 'infrastructure/javelin/api');
 phutil_require_module('phabricator', 'view/base');
 phutil_require_module('phabricator', 'view/form/base');
 phutil_require_module('phabricator', 'view/form/control/submit');
diff --git a/src/applications/differential/view/revisioncomment/DifferentialRevisionCommentView.php b/src/applications/differential/view/revisioncomment/DifferentialRevisionCommentView.php
index cb9bab5604..2ef005669a 100644
--- a/src/applications/differential/view/revisioncomment/DifferentialRevisionCommentView.php
+++ b/src/applications/differential/view/revisioncomment/DifferentialRevisionCommentView.php
@@ -21,6 +21,7 @@ final class DifferentialRevisionCommentView extends AphrontView {
   private $comment;
   private $handles;
   private $markupEngine;
+  private $preview;
 
   public function setComment($comment) {
     $this->comment = $comment;
@@ -37,6 +38,11 @@ final class DifferentialRevisionCommentView extends AphrontView {
     return $this;
   }
 
+  public function setPreview($preview) {
+    $this->preview = $preview;
+    return $this;
+  }
+
   public function render() {
 
     require_celerity_resource('phabricator-remarkup-css');
@@ -48,7 +54,11 @@ final class DifferentialRevisionCommentView extends AphrontView {
 
     $action_class = 'differential-comment-action-'.phutil_escape_html($action);
 
-    $date = date('F jS, Y g:i:s A', $comment->getDateCreated());
+    if ($this->preview) {
+      $date = 'COMMENT PREVIEW';
+    } else {
+      $date = date('F jS, Y g:i:s A', $comment->getDateCreated());
+    }
 
     $author = $this->handles[$comment->getAuthorPHID()];
     $author_link = $author->renderLink();
@@ -70,12 +80,12 @@ final class DifferentialRevisionCommentView extends AphrontView {
           "<p>{$author_link} {$verb} this revision.</p>".
         '</div>';
     }
-    
+
     $background = null;
     $uri = $author->getImageURI();
     if ($uri) {
       $background = "background-image: url('{$uri}');";
-    } 
+    }
 
     return
       '<div class="differential-comment '.$action_class.'">'.
diff --git a/src/view/form/control/base/AphrontFormControl.php b/src/view/form/control/base/AphrontFormControl.php
index b35988d64b..48c494b2d8 100755
--- a/src/view/form/control/base/AphrontFormControl.php
+++ b/src/view/form/control/base/AphrontFormControl.php
@@ -24,6 +24,16 @@ abstract class AphrontFormControl extends AphrontView {
   private $name;
   private $value;
   private $disabled;
+  private $id;
+
+  public function setID($id) {
+    $this->id = $id;
+    return $this;
+  }
+
+  public function getID() {
+    return $this->id;
+  }
 
   public function setLabel($label) {
     $this->label = $label;
diff --git a/src/view/form/control/password/AphrontFormPasswordControl.php b/src/view/form/control/password/AphrontFormPasswordControl.php
index cb0f259fbb..ae02ea73f4 100755
--- a/src/view/form/control/password/AphrontFormPasswordControl.php
+++ b/src/view/form/control/password/AphrontFormPasswordControl.php
@@ -30,6 +30,7 @@ class AphrontFormPasswordControl extends AphrontFormControl {
         'name'      => $this->getName(),
         'value'     => $this->getValue(),
         'disabled'  => $this->getDisabled() ? 'disabled' : null,
+        'id'        => $this->getID(),
       ));
   }
 
diff --git a/src/view/form/control/select/AphrontFormSelectControl.php b/src/view/form/control/select/AphrontFormSelectControl.php
index d2ffaad74d..fdb6a58080 100755
--- a/src/view/form/control/select/AphrontFormSelectControl.php
+++ b/src/view/form/control/select/AphrontFormSelectControl.php
@@ -50,6 +50,7 @@ class AphrontFormSelectControl extends AphrontFormControl {
       array(
         'name'      => $this->getName(),
         'disabled'  => $this->getDisabled() ? 'disabled' : null,
+        'id'        => $this->getID(),
       ),
       implode("\n", $options));
   }
diff --git a/src/view/form/control/text/AphrontFormTextControl.php b/src/view/form/control/text/AphrontFormTextControl.php
index f8265188af..185ffd6a7e 100755
--- a/src/view/form/control/text/AphrontFormTextControl.php
+++ b/src/view/form/control/text/AphrontFormTextControl.php
@@ -30,6 +30,7 @@ class AphrontFormTextControl extends AphrontFormControl {
         'name'      => $this->getName(),
         'value'     => $this->getValue(),
         'disabled'  => $this->getDisabled() ? 'disabled' : null,
+        'id'        => $this->getID(),
       ));
   }
 
diff --git a/src/view/form/control/textarea/AphrontFormTextAreaControl.php b/src/view/form/control/textarea/AphrontFormTextAreaControl.php
index 55ec143551..36b64a8b53 100755
--- a/src/view/form/control/textarea/AphrontFormTextAreaControl.php
+++ b/src/view/form/control/textarea/AphrontFormTextAreaControl.php
@@ -20,7 +20,7 @@ class AphrontFormTextAreaControl extends AphrontFormControl {
 
   const HEIGHT_VERY_SHORT = 'very-short';
   const HEIGHT_SHORT      = 'short';
-  
+
   private $height;
 
   public function setHeight($height) {
@@ -48,6 +48,7 @@ class AphrontFormTextAreaControl extends AphrontFormControl {
         'name'      => $this->getName(),
         'disabled'  => $this->getDisabled() ? 'disabled' : null,
         'class'     => $height_class,
+        'id'        => $this->getID(),
       ),
       phutil_escape_html($this->getValue()));
   }
diff --git a/webroot/rsrc/css/application/differential/add-comment.css b/webroot/rsrc/css/application/differential/add-comment.css
new file mode 100644
index 0000000000..99be1e9f7f
--- /dev/null
+++ b/webroot/rsrc/css/application/differential/add-comment.css
@@ -0,0 +1,23 @@
+/**
+ * @provides differential-revision-add-comment-css
+ */
+
+.differential-add-comment-panel .aphront-form-view {
+  background: #fffff5;
+}
+
+.differential-add-comment-panel .differential-panel {
+  margin-bottom: 0;
+}
+
+.differential-comment-preview {
+  background: #f0f0f0;
+  border-bottom: 1px solid #aaaaaa;
+  margin-bottom: 2em;
+  max-width: 1120px;
+  padding: 15px 20px;
+}
+
+.differential-comment-preview .differential-loading-text {
+  color: #aaaaaa;
+}
diff --git a/webroot/rsrc/js/application/differential/behavior-comment-preview.js b/webroot/rsrc/js/application/differential/behavior-comment-preview.js
new file mode 100644
index 0000000000..41bdec070b
--- /dev/null
+++ b/webroot/rsrc/js/application/differential/behavior-comment-preview.js
@@ -0,0 +1,50 @@
+/**
+ * @provides javelin-behavior-differential-feedback-preview
+ * @requires javelin-lib-dev
+ */
+
+JX.behavior('differential-feedback-preview', function(config) {
+
+  var action = JX.$(config.action);
+  var content = JX.$(config.content);
+  var preview = JX.$(config.preview);
+
+  var aval = null;//action.value;
+  var cval = null;//content.value;
+  var defer = null;
+  var min = null;
+  var request = null;
+
+  function check() {
+    if (request || (min && (new Date().getTime() < min))) {
+      // Waiting on an async or just got one back, rate-limit.
+      return;
+    }
+
+    defer && defer.stop();
+
+    if (action.value !== aval || content.value !== cval) {
+      aval = action.value;
+      cval = content.value;
+
+      request = new JX.Request(config.uri, function(r) {
+        preview && JX.DOM.setContent(preview, JX.HTML(r));
+        min = new Date().getTime() + 500;
+        defer && defer.stop();
+        defer = JX.defer(check, 500);
+      });
+      request.listen('finally', function() { request = null; });
+      request.setData({action : aval, content : cval});
+      // If we don't get a response back soon, retry on the next action.
+      request.setTimeout(2000);
+      request.send();
+    } else {
+      defer = JX.defer(check, 2000);
+    }
+  }
+
+  JX.DOM.listen(content, 'keydown', null, check);
+  JX.DOM.listen(action,  'change',  null, check);
+
+  check();
+});