HttpUtility not recognised in .Net 4.5

WebUtility

You also have another possibility: Use the WebUtility class. The WebUtility class is recommended by Microsoft itself and should be used outside of web applications.

Like the HttpUtility class it also provides you with the possibility to encode and decode URLs.

This way you don't have the problems with importing the library into your project or setting some specific profiles.

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From the Documentation (Source)

The HttpUtility class is used internally by the HttpServerUtility class, whose methods and properties are exposed through the intrinsic ASP.NET Server object. Additionally, the HttpUtility class contains encoding and decoding utility methods that are not accessible from the Server.

To encode or decode values outside of a web application, use the WebUtility class.

The problem is somewhere else.

As you can see in MSDN the HttpUtility class is present in System.Web in .NET Framework 4.5.

You're probably targeting the Client Profile: target the full framework in Project Properties. Otherwise:

• either you did not add the right using statement using System.Web;
• or you did not add the reference to System.Web.dll in the project.