diff --git a/src/main/scala/gitbucket/core/plugin/CompletionProposalProvider.scala b/src/main/scala/gitbucket/core/plugin/CompletionProposalProvider.scala
new file mode 100644
index 0000000..a92e753
--- /dev/null
+++ b/src/main/scala/gitbucket/core/plugin/CompletionProposalProvider.scala
@@ -0,0 +1,33 @@
+package gitbucket.core.plugin
+
+import gitbucket.core.controller.Context
+import gitbucket.core.util.EmojiUtil
+
+trait CompletionProposalProvider {
+
+  val id: String
+  val prefix: String
+  val suffix: String = " "
+  val values: Seq[String]
+
+  def template(implicit context: Context): String = "value"
+  def additionalScript(implicit context: Context): String = ""
+}
+
+class EmojiCompletionProposalProvider extends CompletionProposalProvider {
+  override val id: String = "emoji"
+  override val values: Seq[String] = EmojiUtil.emojis.toSeq
+  override val prefix: String = ":"
+  override val suffix: String = ": "
+  override def template(implicit context: Context): String =
+    s"""'<img src=\"${context.path}/assets/common/images/emojis/' + value + '.png\" class=\"emoji\"></img>' + value"""
+}
+
+class UserCompletionProposalProvider extends CompletionProposalProvider {
+  override val id: String = "user"
+  override val values: Seq[String] = Nil
+  override val prefix: String = "@"
+  override def template(implicit context: Context): String = "'@' + value"
+  override def additionalScript(implicit context: Context): String =
+    s"""$$.get('${context.path}/_user/proposals', { query: '' }, function (data) { user = data.options; });"""
+}
\ No newline at end of file
diff --git a/src/main/scala/gitbucket/core/plugin/Plugin.scala b/src/main/scala/gitbucket/core/plugin/Plugin.scala
index 62b2ccb..3478d5b 100644
--- a/src/main/scala/gitbucket/core/plugin/Plugin.scala
+++ b/src/main/scala/gitbucket/core/plugin/Plugin.scala
@@ -170,6 +170,16 @@
   def textDecorators(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[TextDecorator] = Nil
 
   /**
+   * Override to add completion proposal provider.
+   */
+  val completionProposalProvider: Seq[CompletionProposalProvider] = Nil
+
+  /**
+   * Override to add completion proposal provider.
+   */
+  def completionProposalProvider(registry: PluginRegistry, context: ServletContext, settings: SystemSettings): Seq[CompletionProposalProvider] = Nil
+
+  /**
    * This method is invoked in initialization of plugin system.
    * Register plugin functionality to PluginRegistry.
    */
@@ -219,6 +229,9 @@
     (textDecorators ++ textDecorators(registry, context, settings)).foreach { textDecorator =>
       registry.addTextDecorator(textDecorator)
     }
+    (completionProposalProvider ++ completionProposalProvider(registry, context, settings)).foreach { completionProposalProvider =>
+      registry.addCompletionProposalProvider(completionProposalProvider)
+    }
   }
 
   /**
diff --git a/src/main/scala/gitbucket/core/plugin/PluginRegistory.scala b/src/main/scala/gitbucket/core/plugin/PluginRegistory.scala
index e3a7f2a..c867d35 100644
--- a/src/main/scala/gitbucket/core/plugin/PluginRegistory.scala
+++ b/src/main/scala/gitbucket/core/plugin/PluginRegistory.scala
@@ -43,9 +43,13 @@
   private val dashboardTabs = new ListBuffer[(Context) => Option[Link]]
   private val assetsMappings = new ListBuffer[(String, String, ClassLoader)]
   private val textDecorators = new ListBuffer[TextDecorator]
+  // TODO
   textDecorators += new TextDecorator {
     override def decorate(text: String)(implicit context: Context): String = EmojiUtil.convertEmojis(text)
   }
+  private val completionProposalProviders = new ListBuffer[CompletionProposalProvider]
+  completionProposalProviders += new EmojiCompletionProposalProvider()
+  completionProposalProviders += new UserCompletionProposalProvider()
 
   def addPlugin(pluginInfo: PluginInfo): Unit = plugins += pluginInfo
 
@@ -136,6 +140,10 @@
   def addTextDecorator(textDecorator: TextDecorator): Unit = textDecorators += textDecorator
 
   def getTextDecorators: Seq[TextDecorator] = textDecorators.toSeq
+
+  def addCompletionProposalProvider(completionProposalProvider: CompletionProposalProvider): Unit = completionProposalProviders += completionProposalProvider
+
+  def getCompletionProposalProviders: Seq[CompletionProposalProvider] = completionProposalProviders.toSeq
 }
 
 /**
diff --git a/src/main/scala/gitbucket/core/view/helpers.scala b/src/main/scala/gitbucket/core/view/helpers.scala
index 34c01f1..91317e4 100644
--- a/src/main/scala/gitbucket/core/view/helpers.scala
+++ b/src/main/scala/gitbucket/core/view/helpers.scala
@@ -315,6 +315,14 @@
     case CommitState.FAILURE => "Failed"
   }
 
+  /**
+   * Render a given object as the JSON string.
+   */
+  def json(obj: AnyRef): String = {
+    implicit val formats = org.json4s.DefaultFormats
+    org.json4s.jackson.Serialization.write(obj)
+  }
+
   // This pattern comes from: http://stackoverflow.com/a/4390768/1771641 (extract-url-from-string)
   private[this] val detectAndRenderLinksRegex = """(?i)\b((?:https?://|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,13}/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'".,<>?«»“”‘’]))""".r
 
diff --git a/src/main/twirl/gitbucket/core/helper/attached.scala.html b/src/main/twirl/gitbucket/core/helper/attached.scala.html
index aaed7c4..d1d5557 100644
--- a/src/main/twirl/gitbucket/core/helper/attached.scala.html
+++ b/src/main/twirl/gitbucket/core/helper/attached.scala.html
@@ -1,5 +1,6 @@
 @(owner: String, repository: String, completion: Seq[String], generateScript: Boolean = true)(textarea: Html)(implicit context: gitbucket.core.controller.Context)
 @import gitbucket.core.util.{FileUtil, EmojiUtil}
+@import gitbucket.core.view.helpers
 <div class="muted attachable">
   @textarea
   <div class="clickable">Attach images or documents by dragging &amp; dropping, or selecting them.</div>
@@ -7,47 +8,32 @@
 @defining("(id=\")([\\w\\-]*)(\")".r.findFirstMatchIn(textarea.body).map(_.group(2))){ textareaId =>
 <script>
 $(function(){
-  @if(completion.contains("emoji")){
-    var emojis = @Html(EmojiUtil.emojis.map("\"" + _ + "\"").mkString("[", ", ", "]"));
-  }
-  @if(completion.contains("user")){
-    var users  = [];
-    $.get('@context.path/_user/proposals', { query: '' }, function (data) { users = data.options; });
-  }
-
-  $('#@textareaId').textcomplete([
-    @if(completion.contains("emoji")){
-      {
-        id: 'emoji',
-        match: /\B:([\-+\w]*)$/,
-        search: function (term, callback) {
-          callback($.map(emojis, function (emoji) {
-            return emoji.indexOf(term) === 0 ? emoji : null;
-          }));
-        },
-        template: function (value) {
-          return '<img src="@context.path/assets/common/images/emojis/' + value + '.png" class="emoji"></img>' + value;
-        },
-        replace: function (value) {
-          return ':' + value + ': ';
-        },
-        index: 1
-      },
+  @gitbucket.core.plugin.PluginRegistry().getCompletionProposalProviders.map { provider =>
+    @if(completion.contains(provider.id)){ // TODO Filter by context
+      var @provider.id = @Html(helpers.json(provider.values));
+      @Html(provider.additionalScript)
     }
-    @if(completion.contains("user")){
-      {
-        id: 'user',
-        match: /\B@@([\-+\w]*)$/,
-        search: function (term, callback) {
-          callback($.map(users, function (word) {
-            return word.indexOf(term) === 0 ? word : null;
-          }));
+  }
+  $('#@textareaId').textcomplete([
+    @gitbucket.core.plugin.PluginRegistry().getCompletionProposalProviders.map { provider =>
+      @if(completion.contains(provider.id)){ // TODO Filter by context
+        {
+          id: '@{provider.id}',
+          match: /\B@{provider.prefix}([\-+\w]*)$/,
+          search: function (term, callback) {
+            callback($.map(@{provider.id}, function (proposal) {
+              return proposal.indexOf(term) === 0 ? proposal : null;
+            }));
+          },
+          template: function (value) {
+            return @{Html(provider.template)};
+          },
+          replace: function (value) {
+            return '@{provider.prefix}' + value + '@{provider.suffix}';
+          },
+          index: 1
         },
-        index: 1,
-        replace: function (word) {
-          return '@@' + word + ' ';
-        }
-      },
+      }
     }
   ], {
     onKeydown: function (e, commands) {