Is null valid JSON (4 bytes, nothing else)

Question

Hot debate today:

Is the text stream null valid JSON?

According to http://www.ietf.org/rfc/rfc4627.txt?number=4627:

...
2. JSON Grammar

A JSON text is a sequence of tokens. The set of tokens includes six structural characters, strings, numbers, and three literal names.

A JSON text is a serialized object or array.

Should this interpreted as both statements must be true in order for the text to be valid JSON?

• http://code.google.com/p/json-framework/issues/detail?id=49 seems to indicate (at the bottom) that this is invalid.
• http://json.parser.online.fr/ also flags this as invalid.

However, many other libraries seem to permit it, and indeed, it seems like a single valid token could be a legitimate result.

Is there a definitive answer?

Deafen

Answer 1

[Note! This answer is no longer correct, see answer by @niksnut.]

Yes, both statements must be true. The literal token null is a JSON value. A JSON text is a serialized object or array, which requires {} or [].

Cribwork

How does it come then that most JSON parsers out there accept `null' as valid document? A typical examples are Node.JS (JSON.parse('null') => null or echo 'null' | python -mjson.tool => null. – Daltondaltonism

echo '7' | python -mjson.tool yields 7, so I infer that tool apparently is willing to parse isolated JSON literal values as well as complete (object or array) JSON texts. – Cribwork

Ruby’s JSON parser rejects just null as a value by default: ruby -r json -e 'JSON.parse("null")' givens “unexpected token at 'null' (JSON::ParserError)” – Mollescent

Some parsers also choke on "[]". – Seafarer

Note! This answer is no longer correct, see @Hickie answer below – Colloquium

@moderators: (if any listening) Should we as community edit this answer with warning that it's outdated? – Glimpse

Answer 2

RFC 7159 and its successor RFC 8259 drop the limitation that a JSON text must be an object or an array. The grammar specifies:

JSON-text = ws value ws

where

value = false / null / true / object / array / number / string

Thus, "null" is now a valid JSON document.

Hickie