[wtetzner]

It's a valid subset of Javascript (or at least was initially meant to be), but a JSON object (as opposed to an array) isn't a valid stand-alone Javascript expression, and an attempt to eval it will return an error:

    > eval('{"key": "value"}');
    SyntaxError: missing ; before statement

You can get around this by using parens:

    > eval('({"key": "value"})');
    Object { key: "value" }

But accidentally including a JSON URL in a script tag should fail to evaluate if there's an object at the top level.