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A gulp plugin to apply web.config transforms. You can use this plugin for using gulp with Visual Studio solutions to produce various configurations. This is especially useful when upgrading legacy web applications to ASP.NET 5 since the web.config isn't natively supported.

Transformations While Debugging Locally

Legacy applications that rely on web.config transformations often use Visual Studio plugins like SlowCheetah and Fast Koala to perform transforms in the development environment because MSBuild only transforms the web.config upon deployment, not debugging.

Changes in ASP.NET 5

With ASP.NET 5 applications, the web.config has been deprecated and should only contain a registration for a request handler to make the ASP.NET application backwards compatible on IIS. All remaining configuration settings should be handled by JSON configuration files and with middleware registered in the StartUp class.

Additionally, ASP.NET is no longer compiled by MSBuild, but, rather, the new .NET Execution environment (DNX). With this change, MSBuild targets files (.csproj, .vbproj) are no longer needed.

Unfortunately, while migrating legacy applications to ASP.NET 5, the web.config and its transformations may still be necessary. But, without targets files, utilities like SlowCheetah and Fast Koala become obsolete. Visual Studio 2015 relies on Gulp tasks to handle any pre- and post- build steps. By using gulp-config-transform, you can perform the necessary config transformations for both, debug and production, environments.


Install the package with NPM and add it to your development dependencies.
npm install gulp-config-transform --save-dev


var config-transform = require('gulp-config-transform');

gulp.task('transform', function() {
    var options = { transform : 'Web.Debug.config' }


  • config
    The path of the web.config.
    Default: ./web.config

  • transform
    The path of the transformation configuration.
    Default: ./web.Debug.config

  • destination
    The output path of the transformed web.config.
    Default: ./wwwroot/web.config

  • netVersion
    The version of MSBuild. Accepted values are '4' or '2'.
    Default: 4

  • framework
    The target framework for the build. Accepted values are 'x86' or 'x64'.
    Default: x64

  • msBuildPath
    The full path to the MSBuild executable in order to perform the transform. The path is determined based on the netVersion and framework options. However, if an alternative path is specified, that path will be used instead.
    Default: resolved based on netVersion and framework

  • assemblyFile
    The path of the assembly file for MSBuild to use in order to conduct the web transformation targets. The path is attempted to be resolved automatically by the plugin. But, if it cannot be found or you would like to specify an alternative path, you will need to specify the path as an option.
    The default to this path depends on the current .NET SDK (which is also included with Visual Studio) that is installed on your machine, but the path is typically something like:

    C:\Program Files (x86)\MSBuild\Microsoft\VisualStudio\v10.0\Web\Microsoft.Web.Publishing.Tasks.dll

    The v10.0 can range from v10.0-v15.0.
    Default: resolved automatically

Known Issues / Workarounds

If a transformed configuration file is not created and no error is thrown try running the gulp command as an Administrator.

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npm i gulp-config-transform

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