diff --git a/docs-web/src/main/webapp/app/docs/controller/Tag.js b/docs-web/src/main/webapp/app/docs/controller/Tag.js
index bdd34d05..32b73b94 100644
--- a/docs-web/src/main/webapp/app/docs/controller/Tag.js
+++ b/docs-web/src/main/webapp/app/docs/controller/Tag.js
@@ -26,9 +26,9 @@ App.controller('Tag', function($scope, $dialog, $state, Tag, Restangular) {
   };
   
   /**
-   * Validate a tag.
+   * Validate a tag name for duplicate.
    */
-  $scope.validateTag = function(name) {
+  $scope.validateDuplicate = function(name) {
     return !_.find($scope.tags, function(tag) {
       return tag.name == name;
     });
diff --git a/docs-web/src/main/webapp/partial/docs/tag.html b/docs-web/src/main/webapp/partial/docs/tag.html
index 8082fd39..4e1705f9 100644
--- a/docs-web/src/main/webapp/partial/docs/tag.html
+++ b/docs-web/src/main/webapp/partial/docs/tag.html
@@ -2,11 +2,15 @@
   <div class="row-fluid">
     <div class="span4 well text-center">
       <form name="tagForm" novalidate>
-	      <div class="control-group input-prepend input-append input-block-level" ng-class="{ error: !tagForm.name.$valid }">
-	        <span colorpicker class="btn" data-color="#3a87ad" ng-model="tag.color" ng-style="{ 'background': tag.color }">&nbsp;</span>
-	        <input type="text" name="name" placeholder="New tag"
-            ng-maxlength="36" required ng-model="tag.name" ui-validate="'validateTag($value)'">
-	        <button type="submit" class="btn btn-primary" ng-disabled="!tagForm.$valid" ng-click="addTag()">Add</button>
+        <div class="control-group" ng-class="{ error: !tagForm.name.$valid }">
+		      <div class="input-prepend input-append input-block-level">
+		        <span colorpicker class="btn" data-color="#3a87ad" ng-model="tag.color" ng-style="{ 'background': tag.color }">&nbsp;</span>
+		        <input type="text" name="name" placeholder="New tag"
+	            ng-maxlength="36" required ng-model="tag.name" ui-validate="{duplicate: 'validateDuplicate($value)', space: '!$value || $value.indexOf(\' \') == -1' }">
+		        <button type="submit" class="btn btn-primary" ng-disabled="!tagForm.$valid" ng-click="addTag()">Add</button>
+		      </div>
+		      <span class="help-inline" ng-show="tagForm.name.$error.duplicate">This tag already exists</span>
+		      <span class="help-inline" ng-show="tagForm.name.$error.space">Space are not allowed</span>
 	      </div>
       </form>