What is the correct way to format “true” in JSON?

I want to give a simple true response, but according to various JSON parsers, this is not valid JSON:

true

However, PHP and Javascript act like "true" is indeed valid JSON for true, both when encoding and when decoding:

PHP-

echo json_encode( true ); // outputs: true
echo json_decode( true ); // outputs: 1
echo gettype(json_decode( true )); // outputs: boolean

jQuery-

JSON.stringify( true );   // outputs: true
jQuery.parseJSON( true ); // outputs: true
typeof jQuery.parseJSON( true ); // outputs: boolean

So what is the correct way to send a true response formatted as JSON? Are the validators all wrong?

From the RFC :

A JSON text is a serialized object or array.
  JSON-text = object / array

Most parsers don't accept anything as root that isn't an object or an array. Only less strict parsers will accept that your JSON string just contains true.

So your options are

to not use JSON
to wrap your boolean in an object : {"result":true} or an array : [true]

Update:

The situation changed. Newer versions of the JSON specification (see this one) explicitly accept any serialized value as root of a document:

A JSON text is a serialized value. Note that certain previous specifications of JSON constrained a JSON text to be an object or an array. Implementations that generate only objects or arrays where a JSON text is called for will be interoperable in the sense that all implementations will accept these as conforming JSON texts.

It means it's now legally acceptable to use a boolean as unique value. But of course not all libraries in use are updated, which implies using anything other than an object or an array might still be problematic.