New to Telerik UI for ASP.NET AJAX? Download free 30-day trial


This help article treats the optimization of RadEditor's performance when working with large content and/or having many editor's instances on a page.

General Controls Optimizations

You can consider the following setup when optimizing performance of Telerik UI controls.

  • Use the RadScriptManager control on the page instead of the ScriptManager to combine scripts.

  • Set the control's EnableViewState property to false to avoid the ViewState overhead.

  • Use the LightWeight render mode of the editor to reduce the rendered HTML and JavaScript by leveraging HTML5 and CSS3 and delivering semantic HTML to the browser.

  • Always upgrade your Telerik UI suite to the latest official version, because with each release there are many features, improvements and fixes implemented.

Dialog Resources Optimizations

RadEditor uses the DialogOpener control when opening dialogs. DialogOpener, however,uses an ASP ScriptManager control by default, which may lead to an increased number of requests.

You can easily decrease the number of scripts and styles requests of RadEditor dialogs by setting the DialogOpener's EnableTelerikManagers property to true (Example 1). The EnableTelerikManagers property configures the DialogOpener to use the RadScriptManager and RadStyleSheetManager controls, which do the actual resource combining by default.

Example 1: Improve RadEditor's dialog resources optimization by setting the RadEditor.DialogOpener.EnableTelerikManagers property to True.

<telerik:RadEditor RenderMode="Lightweight" ID="RadEditor1" runat="server">
protected void Page_Load(object sender, EventArgs e)
    RadEditor1.DialogOpener.EnableTelerikManagers = true;
Protected Sub Page_Load(sender As Object, e As EventArgs)
    RadEditor1.DialogOpener.EnableTelerikManagers = True
End Sub 

High CPU on server due that the RadEditor's dialog parameters are deserialized with strong encryption.

By default, RadEditor register all _dialogDefinitions which is a pretty long string which may decrease the performance of the page as well as of the server. You can remove all dialog definitions from the dialog opener control after they are populated on the server using the code below:

public partial class _Default : System.Web.UI.Page 
    protected override void OnPreRenderComplete(EventArgs e) 
Public Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Overrides Sub OnPreRenderComplete(ByVal e As EventArgs)
    End Sub
End Class

This will clear the dialog definitions and will reduce the size of the page on the client.

You'll still be able to take advantage of the lightweight dialogs showcased at

<telerik:RadEditor runat="server" ID="RadEditor1" >
            <telerik:EditorTool Name="InsertImage" />
            <telerik:EditorTool Name="InsertLink" />
            <telerik:EditorTool Name="InsertTableLight" />

Working With Large Content - Creating, Editing, Pasting, Loading and Saving Optimizations

There are a couple of main factors responsible for the slow RadEditor's performance when pasting,loading, editing or saving large XHTML / HTML / TXT files, which content size exceeds 100KB:

  • The Undo / Redo mechanism and other maintenance code that ensures the smooth user experience - it gets increasingly cumbersome and time consuming for the browser to execute it if huge content is in the editor. That is why it is recommended to remove the Undo and Redo buttons from the toolbar when editing large content as shown in this article:Removing Toolbar Buttons.

  • The built-in RadEditor's modules are updatable on selection and they could also decrease the content editing abilities when editing huge content. You can see how to remove the modules in this help article:Disable or Hide Modules.

  • In difference with the TextBox control, which does not process the content when submitting it to the server, RadEditorruns more than 12 content filters, which validate the content and make it XHTML compliant. These filters executes regular expressions and DOM methods to validate the content, which slow down the content submission to the server. To disable the built-infilters set the ContentFilters property to None.

  • The content formatting stripping when pasting huge content uses a lot of CPU resources and the browser could freezes for a long period of time depending on the hardware configuration of the client's machine. The developer could configure the editor to not check and strip the formatting of the pasted content by setting the StripFormattingOptions property to "NoneSupressCleanMessage".

  • You can use a single RadEditor instance to edit multiple elements on the page by following the approach from the Setting hidden RadEditor in edit mode on click and putting it in non editable mode onblur KB article.

  • It is important to test the performance only when debugging is disabled. Set <compilation debug="false" /> in the web.config. When it is true, the MS AJAXdebugging code causes a severe performance hit on the client-side. The fact that most of the editor functionalities implemented in JavaScript, thus resulting in 10 times slower performance compared to native compiled code.

Toolbar Loading Optimizations

When multiple RadEditor instances are present on the same page, the size and the loading time can be optimized significantly by reducing the HTML markup and the JSON sent from the server to the client. This can be done through:

  • ToolProviderID property that lets you share common tools among multiple instances of RadEditor.ToolbarMode property that lets you initialize the tools not at page load, but when an editor is to be used for the first time.

More detailed information on the topic is available in Toolbar Loading Optimizations help article.

See Also

In this article