editorjs-2.x-dev/modules/prism/config/schema/editorjs_prism.schema.yml

editorjs.widget.tool.prism_code:
  type: editorjs.widget.tool.*
  label: 'PrismJs code tool settings'
  mapping:
    settings:
      type: mapping
      mapping:
        placeholder:
          type: string
          label: 'Placeholder'
        languages:
          type: string
          label: 'Language list.'