Click the Submit button below the editor or the Save toolbar button to validate the editor content.

You can validate the UltimateEditor control on the client-side before the page is submitted to ensure that
the user enters content in it.

All you need is to add a CustomValidator control, which comes with .NET Framework, to your page
and set its ControlToValidate property to the ID of your UltimateEditor control and ClientValidationFunction
property to the custom client-side script function used for validation as follows:

<asp:CustomValidator id="CustomValidator1" runat="server"
ErrorMessage="* Please fill in the editor content."
ControlToValidate="UltimateEditor1" ClientValidationFunction="ClientValidate" />

You can define the custom client-side script function by checking whether the editor content is empty.

You can also call the Page_ClientValidate method on the client-side for the toolbar items having their
PostBackValue property set such as the Save button in order to validate the editor content on the client-side.