App Service Editor
App Service Editor, formerly known as Visual Studio Online (Monaco), is a web-based editor for App Service. To access the editor, go to App Service Editor (Preview) in the Development Tools section of the left-hand navigation of your app.
To learn more about the features of App Service Editor, see the video series Visual Studio Online "Monaco".
When you have the App Service Continuous Deployment feature enabled, you should be careful when editing your site code in App Service Editor. Any changes that you make will be reflected in the running site, but any future deployments will overwrite your changes. If you are editing an app with Continuous Deployment enabled, you'll see a warning in App Service Editor.
To learn more, see Continuous Deployment to Azure App Service.