The following test failed as Java string length function returns 4 instead of 2 for those special characters. Similar test in MinLength failed too. [ { "description": "maxLength validation", "schema": {"maxLength": 2}, "tests": [ { "description": "two supplementary Unicode code points is long enough", "data": "\uD83D\uDCA9\uD83D\uDCA9", "valid": true } ] } ]