This service is the numerical version of Cows and Bulls game! it will randomly generate a 4-digit number without duplicate numbers! Haven't played Cows and Bulls before? The built-in teach mode would lead you to understand the rules! ✪Update: 1. Change the infrastructure 2. Added support language 🌐 List of supported languages: Traditional Chinese (Taiwan), Traditional Chinese (Hong Kong), English, Japanese,Korean,Thai [Wikipedia definition] Bulls and Cows is an old code-breaking mind or paper and pencil game for two or more players, predating the commercially marketed board game Mastermind. For details, you can get it on Wikipedia: https://en.wikipedia.org/wiki/Bulls_and_Cows