Python 3.4.0+ (3.4:d994d75cce95, May  6 2014, 21:37:02) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import json
>>> json.loads('''[
...           "boys": 10,
...           "girls": 20,
...          ]''')
Traceback (most recent call last):
   ...
ValueError: Expecting ',' delimiter: line 2 column 17 (char 18)
>>> json.loads("['python', 'perl', 'ruby']")
Traceback (most recent call last):
   ...
ValueError: Expecting value: line 1 column 2 (char 1)
>>> json.loads("[[10, 20], [30, 40]]]")
Traceback (most recent call last):
   ...
ValueError: Extra data: line 1 column 21 - line 1 column 22 (char 20 - 21)

See issue 16009 for when this was added. Can you improve these? (The first one looks odd...)  If so, you could reopen this.