@nerdponx Yes YoBulk provides a way to write JSON schemas by hand..We have added some custom keyword like validate which is not defined in JSON standard..But our validation engine can understand that..You can pass a javascript function through validate keyword..It's a game changer.. "first_name":{ "type":"string", "format": "first_name", "validate": "(x) => {\r\n let regex = new RegExp(\"([a-z][a-zA-Z]*)\");\r\n return regex.test(x);\r\n }" },