Tools and library for applying XML Document Transformations to e.g. .NET configuration files, or any other XML-structured content.

.NET Core 2.1 introduces the concept of global tools, meaning that you can install dotnet-xdt using the .NET CLI and use it everywhere. One advantage of this approach is that you can use the same command, for both installation and usage, across all platforms.

⚠️ To use global tools, .Net Core SDK 2.1.300 or later is required.

Install dotnet-xdt as a global tool (only once):

dotnet tool install --global dotnet-xdt --version 2.1.0

And then you can apply XDT transforms, from the command-line, anywhere on your PC, e.g.:

dotnet xdt --source original.xml --transform delta.xml --output final.xml

Global tools are not ideal when an application needs to build completely self-contained, without relying on tools installed in the surrounding environment. They are also only available on the latest .NET Core.

Read on if this is a concern for your application.

.NET Core 2.0 and earlier do not support global tools.

The "classic" version of this tool, however, can be installed as a project-level tool on both the latest .NET Core, as well as on previous versions.

The tradeoff is that in this usage model, the tool can only be invoked via dotnet transform-xdt, and only from the folder of the project that references it.

See the project-level dotnet-transform-xdt tool section below for details. A separate repository provides a few self-contained sample projects that use dotnet-transform-xdt for Web.config transformations at publish time.

You can also download a standalone dotnet-xdt.exe that runs on any Windows PC with .NET Framework 4.6.1 installed. It has no external dependencies, nor does it require .NET Core. It might run on Mono, but this scenario is not tested.

Download the latest build of dotnet-xdt.exe from the releases page.

For complete flexibility, reference the cross-platform DotNet.Xdt NuGet package in your application:

dotnet add package DotNet.Xdt --version 2.1.0

You can apply XDT transforms to any XML file, or other XML sources that can be read from and written to a .NET Stream.

Define a class MyXdtLogger that implements IXmlTransformationLogger. Then, apply transformations using code similar to:

var document = new XmlTransformableDocument { PreserveWhitespace = true };

using (var sourceStream = File.OpenRead(sourceFilePath))
using (var transformStream = File.OpenRead(transformFilePath))
using (var transformation = new XmlTransformation(transformStream, new MyXdtLogger()))
{
    document.Load(sourceStream);
    transformation.Apply(document);
}

using (FileStream outputStream = File.Create(outputFilePath))
using (var outputWriter = XmlWriter.Create(outputStream, new XmlWriterSettings { Indent = true }))
{
    document.WriteTo(outputWriter);
}

dotnet-xdt is a global tool that can only be installed on .NET Core 2.1 or later.

dotnet-transform-xdt is an alternative version that can be installed as a project-level tool, on all .NET Core versions.

Note: if you are using project.json tooling (CLI 1.0.0 preview 2 or earlier, or Visual Studio 2015), please refer to the project.json section below.

Run dotnet --version in a command prompt and make sure you're using version 2.0.0 or later.

Create a new folder (XdtSample) and run dotnet new web inside it. Verify that the files XdtSample.csproj and web.config file are present. Create a new file named Web.Release.config inside that folder and set its content to:

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <system.webServer>
    <aspNetCore>
      <environmentVariables xdt:Transform="Insert">
        <environmentVariable name="DOTNET_CLI_TELEMETRY_OPTOUT" value="1" />
      </environmentVariables>
    </aspNetCore>
  </system.webServer>
</configuration>

We will use this sample XDT file to add an environment variable that disables dotnet CLI telemetry when your project is published using the Release configuration. See the MSDN XDT reference for the complete transformation syntax.

Edit the XdtSample.csproj file and inside an <ItemGroup> element, add a reference to this XDT tool. Note that you cannot use the NuGet Package Manager UI in Visual Studio 2017 to CLI tool references; they must currently be added by editing the project file.

  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.DotNet.Xdt.Tools" Version="2.0.0" />
    ... other package references ...
  </ItemGroup>

Run dotnet restore and dotnet build in the XdtSample folder. If you now run dotnet transform-xdt you will see the available options, similar to:

.NET Core XML Document Transformation
Usage: dotnet transform-xdt [options]
Options:
  -?|-h|--help    Show help information
  --xml|-x        The path to the XML file to transform
  --transform|-t  The path to the XDT transform file to apply
  --output|-o     The path where the output (transformed) file will be written
  --verbose|-v    Print verbose messages

So far we added the XDT tool to the project, and now we will invoke it when the project is being published. We want to call it before the built-in publish target that makes sure that the Web.config file has a reference to the aspNetCore handler, because that target always runs when publishing web projects, and it also formats the config file to be nicely indented.

Edit the XdtSample.csproj file and add this snippet at the end, right before the closing </Project> tag:

<Project ToolsVersion="15.0" Sdk="Microsoft.NET.Sdk.Web">
  ... everything else ...

  <Target Name="ApplyXdtConfigTransform" BeforeTargets="_TransformWebConfig">
    <PropertyGroup>
      <_SourceWebConfig>$(MSBuildThisFileDirectory)Web.config</_SourceWebConfig>
      <_XdtTransform>$(MSBuildThisFileDirectory)Web.$(Configuration).config</_XdtTransform>
      <_TargetWebConfig>$(PublishDir)Web.config</_TargetWebConfig>
    </PropertyGroup>
    <Exec
        Command="dotnet transform-xdt --xml &quot;$(_SourceWebConfig)&quot; --transform &quot;$(_XdtTransform)&quot; --output &quot;$(_TargetWebConfig)&quot;"
        Condition="Exists('$(_XdtTransform)')" />
  </Target>
</Project>

Here's a quick rundown of the values above:

• BeforeTargets="_TransformWebConfig" schedules this target to run before the build-in target that adds the aspNetCore handler, as described earlier.
• _SourceWebConfig defines the full path to the Web.config file in your project folder. This will be used as the source (input) for the transformation.
• _XdtTransform defines the full path to the XDT transform file in your project folder to be applied. In this example, we use Web.$(Configuration).config, where $(Configuration) is a placeholder for the publish configuration, e.g. Debug or Release.
• _TargetWebConfig defines the path where the transformed Web.config file will be written to, in the publish folder.
• Exec Command invokes the XDT transform tool, passing the paths to the input file (Web.config), transform file (e.g. Web.Release.config) and target file (<publish-folder>\Web.config).
• Exec Condition prevents the XDT transform tool from running if a transform file for a particular publish configuration does not exist (e.g. Web.Debug.config).

Now run dotnet publish in the XdtSample folder, and examine the Web.config in the publish output folder (bin\Debug\netcoreapp2.0\publish\Web.config). It should look similar to this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <handlers>
      <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
    </handlers>
    <aspNetCore processPath="dotnet" arguments=".\XdtSample.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false" />
  </system.webServer>
</configuration>

Since we have not defined a Web.Debug.config file, no transformation occured.

Now let's publish again, but this time using the Release configuration. Run dotnet publish -c Release in the XdtSample folder, and examine the bin\Release\netcoreapp2.0\publish\Web.config file. It should look similar to this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <handlers>
      <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
    </handlers>
    <aspNetCore processPath="dotnet" arguments=".\XdtSample.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" forwardWindowsAuthToken="false">
      <environmentVariables>
        <environmentVariable name="DOTNET_CLI_TELEMETRY_OPTOUT" value="1" />
      </environmentVariables>
    </aspNetCore>
  </system.webServer>
</configuration>

Note that under <aspNetCore>, the <environmentVariables> section was inserted, as configured in the Web.Release.config file.

{
  ... other settings ...
  "tools": {
    "Microsoft.DotNet.Xdt.Tools": "1.0.0"
  }
}

{
  "scripts": {
    "postpublish": [
        "dotnet transform-xdt --xml \"%publish:ProjectPath%\\Web.config\" --transform \"%publish:ProjectPath%\\Web.%publish:Configuration%.config\" --output \"%publish:OutputPath%\\Web.config\"",
        "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%"
	]
  }
}

.NET Core XML Document Transformation
Usage: dotnet transform-xdt [options]
Options:
  -?|-h|--help    Show help information
  --xml|-x        The path to the XML file to transform
  --transform|-t  The path to the XDT transform file to apply
  --output|-o     The path where the output (transformed) file will be written
  --verbose|-v    Print verbose messages