I don't see a grammar I could use for an external standard there. I could be missing it. And I assume there must be one implied, since it appears to be a read-write format. However such things have a nasty habit of turning out upon further inspection to not be as generic as supposed and have local idioms buried in them, often in surprising places. Even JSON, simple as it is, had that problem, and it is after all a subset in an attempt to squeeze out those localisms.

Is it compatible with Common Lisp, such that all such s-expressions will be compatible with it in some natural way?

Grammar is here [0].

ps. there is also jq like cli [1].

[0] https://github.com/janestreet/sexplib/blob/master/src/parser...

[1] https://github.com/janestreet/sexp