CheckAC is a Chrome add-on developed by CheckAC that allows users to quickly determine if they have solved a particular problem on various Online Judge platforms. With CheckAC, users can easily keep track of their solved problems and avoid the frustration of encountering a problem they have already solved.

One of the main features of CheckAC is its ability to automatically fetch the user's solved problems based on their OJ account name. This feature currently supports POJ, ZOJ, and NJUST OJ platforms, and marks the solved problems with a checkmark for easy identification. This eliminates the need for users to manually search for and verify if they have solved a specific problem.

CheckAC also provides a convenient jump-to-problem functionality. Users can simply click on the CheckAC icon and enter the desired problem number to quickly navigate to that problem. Before jumping to the problem, CheckAC even provides color-coded indications to inform users if they have already solved the problem, further enhancing the user experience.

Additionally, CheckAC offers a ToDo List feature, allowing users to easily add problems they plan to solve in the future. This feature enables users to keep track of their goals and conveniently jump to these problems whenever they are ready.

Furthermore, CheckAC provides a simple Follow feature, which aggregates the solved problem count of users the user is following on POJ and ZOJ platforms. This feature allows users to stay updated with the progress of their friends or other users they are interested in.

With its user-friendly interface and helpful features, CheckAC is a valuable tool for OJ enthusiasts who want to efficiently manage their solved problems and stay organized in their problem-solving journey.