The SharePoint Workbench

• SharePoint Workbench is a developer design surface that enables you to quickly preview and test web parts without deploying them in SharePoint. SharePoint workbench can be accessed from any SharePoint site in your tenancy using following URL:
• SharePoint Site Workbench

http://sharepoint-site-url/_layouts/15/workbench.aspx

• Local Workbench

https://localhost:4321/temp/workbench.html

• Whenever you run your SPFx web part, Local Workbench is automatically launched in the browser and you can preview your web part. Any changes that you make in your web part code will be automatically reflected in local workbench. Local Workbench is not connected to SharePoint list.

• You have to manually run SharePoint Workbench by typing the URL in the browser. Any changes that you make in your web part code will not be reflected in the web part unless you refresh it. SharePoint Workbench is connected to your SharePoint Site Collection, hence you can access SharePoint list and features of SharePoint to test your web part.