T4 Assembly Directive


This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, use the version selector at the top left. We recommend upgrading to Visual Studio 2019. Download it here

In a Visual Studio design-time text template, the assembly directive loads an assembly so that your template code can use its types. The effect is similar to adding an assembly reference in a Visual Studio project.

For a general overview of writing text templates, see Writing a T4 Text Template.


You do not need the assembly directive in a run-time (preprocessed) text template. Instead, add the necessary assemblies to the References of your Visual Studio project.

Using the Assembly Directive

The syntax of the directive is as follows:

<#@ assembly name="[assembly strong name|assembly file name]" #>

The assembly name should be one of the following:

  • The strong name of an assembly in the GAC, such as System.Xml.dll. You can also use the long form, such as name="System.Xml, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089". For more information, see AssemblyName.

  • The absolute path of the assembly

    You can use the $(variableName) syntax to reference Visual Studio variables such as $(SolutionDir), and %VariableName% to reference environment variables. For example:

<#@ assembly name="$(SolutionDir)\MyProject\bin\Debug\SomeLibrary.Dll" #>

The assembly directive has no effect in a preprocessed text template. Instead, include the necessary references in the References section of your Visual Studio project. For more information, see Run-Time Text Generation with T4 Text Templates.

Standard Assemblies

The following assemblies are loaded automatically, so that you do not need to write assembly directives for them:

  • Microsoft.VisualStudio.TextTemplating.1*.dll

  • System.dll

  • WindowsBase.dll

    If you use a custom directive, the directive processor might load additional assemblies. For example, if you write templates for a domain-specific language (DSL), you do not need to write assembly directives for the following assemblies:

  • Microsoft.VisualStudio.Modeling.Sdk.1*.dll

  • Microsoft.VisualStudio.Modeling.Sdk.Diagrams.1*.dsl

  • Microsoft.VisualStudio.TextTemplating.Modeling.1*.dll

  • The assembly containing your DSL.

Using project properties in both MSBuild and Visual Studio

Visual Studio macros like $(SolutionDir) don’t work in MSBuild. If you want to transform templates in your build machine, you have to use project properties instead.

Edit your .csproj or .vbproj file to define a project property. This example defines a property named myLibFolder:

<!-- Define a project property, myLibFolder: -->

<!-- Tell the MSBuild T4 task to make the property available: -->
    <T4ParameterValues Include="myLibFolder">

Now you can use your project property in text templates, which transform correctly in both Visual Studio and MSBuild:

<#@ assembly name="$(myLibFolder)\MyLib.dll" #>

See Also

T4 Include Directive