I was looking for an AMP plugin in Modx but since now there's no official packages, but I found this https://github.com/Sterc/modx-amp
I dunno how to install it, I read the official documentation but is not so clear and it's a bit outdated. I tryed to put in core/packages and install thru the panel without success. Any helps?
I guess you should create a new plugin within the MODX-backend and paste the content of this file in it:
modx-amp/core/components/amp/elements/plugins/plugin.modxamp.php
But I don't know on which event you want the plugin to get triggered (maybe on "OnWebPagePrerender"?)
The other files should be in your "core/components"-folder.