Setting Up Your Telerik UI for ASP.NET AJAX License Key

Starting with 2025 Q1, Telerik UI for ASP.NET AJAX requires activation through a License Key. The Telerik.Web.UI.dll assembly now depends on Telerik.Licensing.Runtime.dll, available via NuGet (https://www.nuget.org/packages/Telerik.Licensing) or the Telerik UI for ASP.NET AJAX installations.

This article shows how to download your personal license key and activate Telerik UI for ASP.NET AJAX.

If the license is missing or invalid, you will see errors and warnings during build and run-time, such as watermarks and banners.

Choose your licensing method

Because Web Application and Web Site projects differ in structure, the activation steps also differ. Use the table below to quickly pick the correct method.

Project type	Using NuGet	License method
Web Application	Yes	License file (telerik-license.txt)
Web Application	No	Script key in AssemblyInfo
Web Site	No	Script key in App_Code

Quick check: If your project contains a .csproj or .vbproj file, it is a Web Application. Otherwise, it is a Web Site project. For additional background, see:

• Microsoft guidance: Web Application vs Web Site
• Web Site vs Web Application - Key Differences

Now follow the activation steps for your project type:

Web Applications using NuGet

Only Web Application projects that have the Telerik.Licensing package installed from NuGet can be activated using a license file (telerik-license.txt). Otherwise, a Script key (assembly attribute) is required, see Web Applications without NuGet and Web Sites section.

To download and install your Telerik license key file:

1. Go to the License Keys page in your Telerik account.
2. Click the Download License Key button.
3. Save the telerik-license.txt file to your user profile directory %AppData%\Telerik\telerik-license.txt, for example, C:\Users\...\AppData\Roaming\Telerik\telerik-license.txt

This makes the license available to all Telerik applications on the local machine. To scope the license to a single project or solution, place telerik-license.txt in the root folder of that project or solution. The telerik-license.txt is applied during build and does not need to be deployed to the production server.

Web Applications without NuGet and Web Sites

Web Applications projects that do not use NuGet and Web Site projects require an assembly attribute, containing the License Key. Follow the steps below:

1. Go to the License Keys page in your Telerik account.
2. On the Telerik UI for ASP.NET AJAX row, click the Script key link.
3. Select the language (C# KEY or VB KEY) and click the Copy and close button to copy the Script Key to your clipboard.
4. Adding the License Key script:
   • Web Application: Paste the copied key to the Properties > AssemblyInfo
   • Web Site: Add a C#/VB Class file to the App_Code directory of your project, e.g. App_Code\TelerikLicense.cs and paste the Script Key from your clipboard.

To activate the license in other projects, repeat these steps.

License file vs Script key

• License file - supported for Web Application projects that use NuGet. It enables license validation during build and runtime.
• Script key - required for Web Applications that do not use NuGet and for Web Site projects.

The license file method does not work for Web Site projects or for Web Applications that do not use NuGet. Use the Script key in these cases.

How the license is applied based on project type

Project Type	How license is applied	File needed on production server
Web Application using NuGet	License file (telerik-license.txt) is resolved at build time and embedded by the licensing tooling	❌ No
Web Application without NuGet	Script key attribute is compiled into the assembly	❌ No
Web Site Project	Script key file in App_Code is evaluated at runtime	✅ Yes

Explanation

• NuGet Web Applications use the telerik-license.txt only on the development machine. The license is embedded during build.
• Web Applications without NuGet embed the license via an assembly attribute (e.g., in AssemblyInfo.cs or TelerikLicense.cs).
• Web Site projects cannot embed attributes into a compiled assembly, so the license file must remain in App_Code on the server.

See Also

• License Activation Errors and Warnings
• Adding the License Key to CI Services
• Frequently Asked Questions about Your Telerik UI for ASP.NET AJAX License Key
• ASP.NET Web Forms Web Site vs Web Application in Visual Studio - Key Differences Explained
• Fix Telerik UI for ASP.NET AJAX License Error Banner & Watermarks (the NuGet approach)
• Fix Telerik UI License Error in ASP.NET Web Forms site via EvidenceAttribute (App_Code & Precompile)
• Removing the Telerik AJAX license error and watermark in ASP.NET Web Forms application