Develop a Custom Block Widget

To develop and offer a custom block, you need the following:

  • A block widget: an HTML page for editing content that uses the Content Builder Block SDK to interact with content blocks in the editor.
  • A block icon and dragging icon. This icon displays as users drag and drop the block onto the canvas.
  • An app that serves this page and a hosting provider to host the app.
  • An installed package that includes your block component.

When adding a block component to an installed package, provide a block widget URL. This is the registered endpoint for your custom content block app. For example, if the URL for your block widget is, then the Content Builder editor assumes these URLs exist.

  • is your block widget page.
  • is your block icon.
  • is your block drag icon.

To test your block, you need an account that's provisioned for Content Builder, with user permissions to use the editor. Add a block component to your installed package and test it in Content Builder.

To sell or distribute your custom block outside of your account, register your block widget's installed package on AppExchange.