Cognitive diagnosis is an important component of modern measurement theory and has received widespread attention from researchers in the fields of education and psychological measurement. Existing cognitive diagnosis analysis tools rely on professional software packages (such as R packages), which creates significant challenges for users, especially those who are not familiar with computer programming. To remove this technical barrier, our team has developed a web-based, user-friendly platform, named flexCDMs, for cognitive diagnosis data analysis. This article describes the features of the platform, the functional modules, the implemented cognitive diagnosis models (CDMs) and algorithms, and illustrates the operations of the platform. This platform can be used to analyze data based on various cognitive diagnosis models, carry out Q-matrix theory, model-data fit tests, parameter estimation, quality analysis of cognitive diagnostic tests, differential item functioning (DIF) detection, and Q-matrix modification. It produces various charts and graphs to report results. It is a powerful, yet easy to use cognitive diagnosis data analysis tool. The website for the flexCDMs platform is: