Q:

Is `[1,2,3]` valid json format?

I know:
{
   "name": "Mike",
   "age": 18
}

or
[{"name": "Mike"},{"name": "Jeff"}]

are valid jsons.
But I'm not sure if [1,2,3] is or not?

A:

[1,2,3] a valid JSON array, but not a valid JSON object. An object must be of the form {...}.
Your other examples are not valid JSON. Strings must be in double-quotes. You fixed it.

