Are whitespace characters insignificant in JSON?

Yes, blanks outside a double-quoted string literal are ignored in the syntax. Specifically, the ws production in the JSON grammar in RFC 4627 shows:

Insignificant whitespace is allowed before or after any of the six
structural characters.

   ws = *(
             %x20 /              ; Space
             %x09 /              ; Horizontal tab
             %x0A /              ; Line feed or New line
             %x0D                ; Carriage return
         )