JSON can be more compact if it simply used collapsible spaces to delimit elements within an array and key-value pairs within a dictionary. For example:

    [1,[2,3],4,{"a":5,"b":6}] // 25 characters

can be rewritten as:

    [1[2 3]4{"a":5 "b":6}]    // 22 characters

Also, currently, JSON requires all string literals to be quoted. If we relax that constraint and only quote string literals that contain escape characters, we can achieve even more space savings. The above example can be rewritten as:

    [1[2 3]4{a:5 b:6}]        // 18 characters

And, in my opinion, the formatted version (with uncollapsed spaces) is just as readable as the original JSON expression:

    [1 [2 3] 4 {a:5 b:6}]     // 21 characters