The JSON Editor provides an editable tree that makes it easy to create, duplicate, and remove fields, as well as to edit field content.

The bar at the top of the editor provides the following functionality: 

You can extend and modify fields by using the commands available from the command icons. The available commands depend on the field type.
Available commands could include:
Additionally, you can rearrange fields by dragging and dropping a field's drag icon.
Note that when you are working with JSON, a special notation is used for parameterizing a number or boolean field within a JSON message: ${number:<value>} or ${boolean:<value>}. For example, to parameterize a number field with the column Count, you would use ${number:Count}.