MJML Preview Package
Show the rendered HTML from MJML on the right pane of the editor. It is enabled for
To toggle the preview, go to "Packages" > "mjml-preview" > "Preview MJML".
Trigger on Save
To refresh the preview pane on each save, tick the box "Trigger on Save" in the settings of the package: ⌘+, or ctrl+, to open package settings > look for "mjml-preview" in "installed packages" > "Settings" > "Trigger on Save".