AtCoder is a competitive programming platform based in Japan that allows users to participate in coding contests. It was launched in 2012 and has gained popularity among programmers for its diverse range of problems and contests, catering to various skill levels. Participants can solve problems in multiple programming languages and receive instant feedback on their submissions. The platform also features a ranking system, enabling users to track their progress and compare their skills with others. AtCoder hosts regular contests, including beginner-friendly events and more challenging competitions, fostering a community of programmers who can learn and improve together.