There's two plugins needed to run HAX on GravCMS - The web components and HAX plugins.

• Web components plugin - provides the build routine and installation instructions
• HAX plugin - editor capabilities

Enable these and then HAX will show up when you go to edit / add a page. Beware there can be conflicts between HAX and the markdown parsing capabilities of Grav so you may need to disable the markdown parser on pages that use HAX.