I think you sort of answered your question there already. You just do it and catch the errors. No errors: valid, proceed. Errors... you decide what happens next. E.g.-

use warnings;
use strict;
use JSON::XS;
use Try::Tiny;

my %json = (
            empty_obj => "{}",
            empty_array => "[]",
            bare_string => "hai",
            obj => qq|{"o":"hai"}|,
            bad_obj => qq|{o:hai}|,
           );

for my $name ( keys %json )
{
    printf "%11s --> ", $name;
    try {
        my $throw_away = decode_json($json{$name});
        print "OK!\n";
    } catch {
        print "Error: $_";
    };
}
__END__
        obj --> OK!
bare_string --> Error: malformed JSON string, neither array, object, n
+umber, string or atom, at character offset 0 (before "hai") at ...
  empty_obj --> OK!
    bad_obj --> Error: '"' expected, at character offset 1 (before "o:
+hai}") at ...
empty_array --> OK!
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