JSON (JavaScript Object Notation) is a simple data format.
See to and "RFC4627"().

This module converts Perl data structures to JSON and vice versa using either
JSON::XS or JSON::PP.

JSON::XS is the fastest and most proper JSON module on CPAN which must be
compiled and installed in your environment.
JSON::PP is a pure-Perl module which is bundled in this distribution and
has a strong compatibility to JSON::XS.

This module try to use JSON::XS by default and fail to it, use JSON::PP instead.
So its features completely depend on JSON::XS or JSON::PP.