[SamBam]

My understanding is that you would be making your own. E.g. if you had a site that people could comment on, make a url that serializes those comments as JSON and then point this at that.

[shantly]

As pointed out elsewhere by Andrew_nenakhov, we have that already—it's RSS. Or Atom. Or JSON Feed if you really must have JSON for some reason.

[re_dmitriy]

There's no simplicity. REFL.ME is easier. Try it.

[ignoranceprior]

Relevant xkcd: https://xkcd.com/927/