diff --git a/css/jgrowl.css b/css/jgrowl.css
index af8c108b..078c1175 100644
--- a/css/jgrowl.css
+++ b/css/jgrowl.css
@@ -1,6 +1,6 @@
 
 div.jGrowl {
-	z-index: 			1000;
+	z-index: 			1050;
 	color: 				#fff;
 }
 
diff --git a/js/core.js b/js/core.js
index 338ce194..6f11e0f0 100644
--- a/js/core.js
+++ b/js/core.js
@@ -6,12 +6,13 @@ define([
     "extensionMgr",
     "mousetrap",
     "text!html/settingsTemplateTooltip.html",
+    "text!html/settingsUserCustomExtensionTooltip.html",
     "storage",
     "config",
     "libs/bootstrap",
     "libs/layout",
     "libs/Markdown.Editor"
-], function($, _, utils, settings, extensionMgr, mousetrap, settingsTemplateTooltipHTML) {
+], function($, _, utils, settings, extensionMgr, mousetrap, settingsTemplateTooltipHTML, settingsUserCustomExtensionTooltipHTML) {
 
     var core = {};
 
@@ -536,6 +537,20 @@ define([
             trigger: 'hover',
             title: 'Thanks for supporting StackEdit by adding a backlink in your documents!'
         });
+        $(".tooltip-usercustom-extension").tooltip({
+            html: true,
+            container: '#modal-settings',
+            placement: 'right',
+            trigger: 'manual',
+            title: settingsUserCustomExtensionTooltipHTML
+        }).click(function(e) {
+            $(this).tooltip('show');
+            $(document).on("click.tooltip-usercustom-extension", function(e) {
+                $(".tooltip-usercustom-extension").tooltip('hide');
+                $(document).off("click.tooltip-usercustom-extension");
+            });
+            e.stopPropagation();
+        });
         $(".tooltip-template").tooltip({
             html: true,
             container: '#modal-settings',
diff --git a/js/extensionMgr.js b/js/extensionMgr.js
index 64ec4f82..2f1a2e5c 100644
--- a/js/extensionMgr.js
+++ b/js/extensionMgr.js
@@ -26,6 +26,7 @@ define([
     "extensions/buttonHtmlCode",
     "extensions/buttonMarkdownSyntax",
     "extensions/buttonViewer",
+    "extensions/userCustom",
     "libs/bootstrap",
     "libs/jquery.waitforimages"
 ], function($, _, utils, Extension, settings, settingsExtensionsAccordionHTML) {
@@ -37,14 +38,14 @@ define([
         return argument instanceof Extension && argument;
     }).compact().value();
 
-    // Return every named callbacks implemented in extensions
+    // Returns all callbacks with the specified name that are implemented in extensions
     function getExtensionCallbackList(hookName) {
         return _.chain(extensionList).map(function(extension) {
             return extension.config.enabled && extension[hookName];
         }).compact().value();
     }
 
-    // Return a function that calls every callbacks from extensions
+    // Return a function that calls every callbacks with the specified name from all extensions
     function createHook(hookName, noLog) {
         var callbackList = getExtensionCallbackList(hookName);
         return function() {
@@ -69,6 +70,9 @@ define([
         extension.config = _.extend({}, extension.defaultConfig, extensionSettings[extension.extensionId]);
         extension.config.enabled = !extension.isOptional || extension.config.enabled === undefined || extension.config.enabled === true;
     });
+    
+    // Call every onInit callbacks
+    createHook("onInit")();
 
     // Load/Save extension config from/to settings
     extensionMgr["onLoadSettings"] = function() {
diff --git a/js/extensions/userCustom.js b/js/extensions/userCustom.js
new file mode 100644
index 00000000..8370f54a
--- /dev/null
+++ b/js/extensions/userCustom.js
@@ -0,0 +1,63 @@
+define([
+    "jquery",
+    "underscore",
+    "utils",
+    "classes/Extension",
+    "fileSystem",
+    "settings",
+    "text!html/userCustomSettingsBlock.html",
+], function($, _, utils, Extension, fileSystem, settings, userCustomSettingsBlockHTML) {
+
+    var userCustom = new Extension("userCustom", "UserCustom extension", true);
+    userCustom.settingsBlock = userCustomSettingsBlockHTML;
+    userCustom.defaultConfig = {
+        code: "",
+    };
+
+    var fileMgr = undefined;
+    userCustom.onFileMgrCreated = function(fileMgrParameter) {
+        fileMgr = fileMgrParameter;
+    };
+
+    var synchronizer = undefined;
+    userCustom.onSynchronizerCreated = function(synchronizerParameter) {
+        synchronizer = synchronizerParameter;
+    };
+
+    var publisher = undefined;
+    userCustom.onPublisherCreated = function(publisherParameter) {
+        publisher = publisherParameter;
+    };
+
+    var extensionMgr = undefined;
+    userCustom.onExtensionMgrCreated = function(extensionMgrParameter) {
+        extensionMgr = extensionMgrParameter;
+    };
+
+    userCustom.onLoadSettings = function() {
+        utils.setInputValue("#textarea-usercustom-code", userCustom.config.code);
+    };
+
+    userCustom.onSaveSettings = function(newConfig, event) {
+        newConfig.code = utils.getInputValue("#textarea-usercustom-code");
+        try {
+            eval(newConfig.code);
+        }
+        catch(e) {
+            extensionMgr.onError(e);
+            // Mark the textarea as error
+            utils.getInputTextValue("#textarea-usercustom-code", event, /^$/);
+        }
+    };
+
+    userCustom.onInit = function() {
+        try {
+            eval(userCustom.config.code);
+        }
+        catch(e) {
+            console.error(e);
+        }
+    };
+
+    return userCustom;
+});
\ No newline at end of file
diff --git a/js/html/settingsTemplateTooltip.html b/js/html/settingsTemplateTooltip.html
index c586eb64..8d4746df 100644
--- a/js/html/settingsTemplateTooltip.html
+++ b/js/html/settingsTemplateTooltip.html
@@ -7,7 +7,7 @@ Available variables:
 	<li><b>publishAttributes</b>: attributes of the publish location
 		(undefined if not publishing)</li>
 </ul>
-Examples:
+<b>Examples:</b>
 <br />
 &lt;title&gt;&lt;%= documentTitle %&gt;&lt;&#x2F;title&gt;
 <br />
diff --git a/js/html/settingsUserCustomExtensionTooltip.html b/js/html/settingsUserCustomExtensionTooltip.html
new file mode 100644
index 00000000..2dfd1833
--- /dev/null
+++ b/js/html/settingsUserCustomExtensionTooltip.html
@@ -0,0 +1,16 @@
+Extension variable name:
+<b>userCustom</b>
+<br>
+<br>
+<b>Example:</b>
+<br />
+userCustom.onPreviewFinished = function() {
+<br />
+&nbsp;&nbsp;extensionMgr.onMessage(&quot;Finished!&quot;);
+<br />
+};
+<br />
+<br />
+<a target="_blank"
+	href="https://github.com/benweet/stackedit/blob/master/doc/developer-guide.md#architecture">More
+	info</a>
\ No newline at end of file
diff --git a/js/html/userCustomSettingsBlock.html b/js/html/userCustomSettingsBlock.html
new file mode 100644
index 00000000..c2c257c0
--- /dev/null
+++ b/js/html/userCustomSettingsBlock.html
@@ -0,0 +1,12 @@
+<p>Allows users to implement their own extension.</p>
+<div class="form-horizontal">
+	<div class="control-group">
+		<label class="control-label" for="textarea-usercustom-code">JavaScript code
+			<a href="#" class="tooltip-usercustom-extension">(?)</a>
+		</label>
+		<div class="controls">
+			<textarea id="textarea-usercustom-code"></textarea>
+		</div>
+	</div>
+</div>
+<span class="help-block pull-right"><a target="_blank" href="https://github.com/benweet/stackedit/blob/master/doc/developer-guide.md#architecture">More info</a></span>
\ No newline at end of file
diff --git a/run_deploy b/run_deploy
old mode 100644
new mode 100755