API for the posts? JSON in posts?

I was thinking about writing something that could be probably called "plug-in" for this site. I mean: in special section/tag of the post there could be i.e. JSON data - that this plugin will use to change rendering of this post. I'm even thinking about using those tools in browsers that provide so called "user JS scripts" for chosen page. I could probably do it without this site API... but I have to store data somewhere. And I don't want to use browser storage for this - it should be stored "in post body". It could work similar to those interactive character sheets - you have edition, calculation capabilities - but the data is stored in the post. If I will write something good maybe the site owner will consider make it an official "plugin framework". I know there are another 1000 details to consider, but first let's look at possible effects. But to start my experiments I have to have some access to post data - is there something like it? In frontend trough JS, or through backend(REST API maybe? ).

I understood about half of those words.

@Keleth

Yes... I have written it to fast probably. To make it simple: is there API for this site, that normal user can access? I'm most interested in posts data. Edit: testing Edit function network activity... :)

I have asked before but havent gotten anywhere. As fare as I know there is no API. Only the database

As I have checked trough browser dev tools there is definitely api for interactive/custom character sheets. https://api.gamersplane.com/characters/bbformUpdateVal But it's all that I know for now. Maybe will look into it when will have some more time.