The Ajax Control Toolkit was last officially updated in (version 20.1.0). It was built for older WebForms and the now-deprecated System.Web.Extensions . While the runtime can function in .NET Framework 4.8 projects opened in VS2022, the design-time experience is severely degraded. How to Make It Work in VS2022 (If You Must) If you are maintaining a legacy WebForms application and cannot rewrite it yet, follow these steps: 1. Use .NET Framework 4.8 Create or open a project targeting .NET Framework 4.8 . Do not attempt .NET 5+. 2. Install the NuGet Package Skip the old Codeplex installer. Use NuGet:

Introduction The Ajax Control Toolkit (ACT) was once a staple for ASP.NET Web Forms developers. It provided a rich set of 40+ server controls (like CalendarExtender , ModalPopupExtender , and AutoCompleteExtender ) that brought client-side AJAX functionality to traditional postback-heavy web apps.

For existing projects, treat ACT as technical debt. Budget time to refactor those extenders into modern HTML/CSS/JavaScript patterns. Your future self (and your users) will thank you. Have you successfully migrated from ACT? Share your experience in the comments below.