wpackio depends on webpack to create the dev server and production build. It does provide a way to extend and override webpack configuration it creates. Since wpackio can operate in both single and multi compiler mode, we provide method to extend webpack configuration for each of the webpack compiler. The extend option is actually accepted through the files property of project config. Extending through files property As written in the project-configuration section, files is what defines different entry-point of your project and decides whether webpack should be run in single compiler mode or multi-compiler mode (without any compromise). A typical files entry may look like this: wpackio.project.js As you might have guessed, we patch through webpackConfig to extend configuration. Extend with Object Put overriding webpack configuration object and it will be merged with webpack merge. Extend with function Even more flexibility can be obtained by using a callback function. It has the following signature. So it will take four parameters: webpackConfig (Object) : What the system has generated as your webpack config. webpackMergeApi (Function): The webpack merge instance for direct usage. appDir (string): Directory inside outputPath where all the assets are to be emitted. isDev (boolean) : Whether the operation is going for development mode or production build. And it should return a valid webpack configuration object. An example could be Word of caution The consumer PHP library, publicPath, development server and many internals actually depend upon the proper structuring of entry, output and publicPath of webpack configuration. If you override those, then the system may not work correctly. In most of the situations, you would actually want to add more loaders or modify existing loaders. Feel free to do that by changing config.module.rules and you should be good to go.