validation - Are booleans valid JSON

Question

Why do some JSON validators flag a boolean value as invalid JSON, and others as valid? That is, just true or false values (no object).

Valid:

• http://jsonlint.com/
• http://codebeautify.org/jsonvalidator

Invalid:

• https://jsonformatter.curiousconcept.com/

Answer 1

The validator you link to validates the JSON string existing of a mere true as invalid according to RFC 4627, which dictates that the root of a JSON string is to be an array or object:

A JSON text is a serialized object or array.

 JSON-text = object / array

An unwrapped value such as true or "foo" or 42 is not JSON according to that RFC.

The other RFCs it can validate against, RFC 7159 and RFC 8259, deem the above examples valid as it does not constrain a JSON text to objects or arrays, but also allows values:

A JSON value MUST be an object, array, number, or string, or one of the following three literal names:

 false null true

And because the former (RFC 4627) is obsoleted by the latter two (RFC 7159 respectively 8259), true is a valid JSON string.