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

Updated on Oct 1, 2026

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:

Go to the License Keys page in your Telerik account.
Click the Download License Key button.
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:

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

Troubleshooting a Missing License in a Web Application

If a Web Application still reports No license found after telerik-license.txt has been downloaded, verify that the file-based method can actually be used by the project and build process:

Confirm that the project references the Telerik.Licensing NuGet package. A license file alone does not activate a Web Application that does not use this package; use the Script key for a Web Application without NuGet.
Confirm that the file is available to the account performing the build. The supported locations are the active user's %AppData%\Telerik directory and the project or solution root. In CI, provide the file or license environment variable to the build process rather than relying on a developer's profile.
Check whether TELERIK_LICENSE or TELERIK_LICENSE_PATH is set. When multiple activation sources are present, an environment variable can take precedence over a license file; remove stale or invalid values before rebuilding.
Delete stale bin, obj, and publish output, restore packages, and rebuild. Verify that the deployed Telerik.Web.UI.dll and Telerik.Licensing.Runtime.dll come from the intended build. Do not copy telerik-license.txt or a license key into the production artifact for a Web Application.
Distinguish a build warning from a runtime banner or watermark. If the clean build is licensed but the published application still reports a licensing error, inspect the deployed assemblies and confirm that the publish step did not reuse an older artifact.
For build and runtime troubleshooting steps, see Telerik Licensing Diagnostics.

Using the Visual Studio Extensions Upgrade Wizard

The Telerik Visual Studio Extensions Upgrade Wizard provides automated assistance for license activation when upgrading your projects to the latest version of Telerik UI for ASP.NET AJAX.

License Key File Assistance (All Project Types)

When you run the Upgrade Wizard, it automatically checks for the telerik-license.txt file. If the file is not found:

An indicator appears in the top-right corner of the wizard
You can click Download License Key File to download it directly from your Telerik account
You can click Open License Key Location to navigate to the folder where the file should be placed

The wizard checks for the license file in:

Your user profile directory: %AppData%\Roaming\Telerik\telerik-license.txt
The project or solution root folder

The documented Upgrade Wizard workflow does not require a command window, C:\Windows\System32, or administrator access. If a separate CLI is suggested by an account portal, verify that tool and command with Telerik licensing support before using it; this documentation does not define a Telerik CLI license-retrieval command.

Script Key Assistance (Web Site Projects Only)

For Web Site projects, the Upgrade Wizard also validates the Script Key in the App_Code folder:

If the Script Key is missing, the wizard displays a Script Key Required warning
Click the Add Script Key button to automatically download your Script Key
The wizard will create a TelerikLicense.cs (or .vb) file in your App_Code directory on the final step before completing the upgrade

This automated approach simplifies the licensing process and ensures your project is properly licensed after the upgrade.