LLD designer
A free class-diagram tool for low-level design practice. Add classes, interfaces, abstract classes and enums with their fields and methods, and connect them with inheritance, realisation, composition, aggregation, association and dependency. Design checks flag what an interviewer would question, such as a class that inherits from two classes or an interface that holds state. The Java tab turns the diagram into code skeletons, and the Mermaid tab gives text you can paste into docs.