Class Diagram Generator: Plain Words In, UML Out

A UML class diagram is a static view of an object-oriented system. Each box is a class with three compartments: the name, the attributes it stores and the operations it offers. Lines between boxes show how classes relate, and numbers at their ends say how many objects take part.

It is the diagram most often asked for in software design courses, and the one teams sketch before writing code or reviewing a design. A class diagram generator removes the slow part, drawing and aligning the boxes, so the time goes into deciding what the classes should be.

Name the main things and how they are connected: "a customer places many orders", "an order contains order items", "a payment is either by card or by PayPal". These sentences tell the model which classes exist, which way the multiplicities go and where inheritance belongs.

Say which relationships are strong ownership, where the part cannot exist without the whole, so they become composition. If you already know key fields or methods, list them; otherwise sensible ones are added. Keep one diagram to one area of the system for a readable result, then ask the class diagram generator to add the rest later with AI edits.

Check the arrows first. A hollow triangle means inheritance and should point at the parent class. A filled diamond is composition and sits at the owner's end; a hollow diamond is aggregation. A plain open arrow is an association, and a dashed one is a dependency.

Then read the multiplicities as sentences, for example "one customer has zero or more orders". If one reads wrong, change it in the editor or ask the AI to fix it. Finally, check visibility: fields are usually private and methods public.

Class diagrams and ER diagrams look alike but answer different questions. A class diagram models objects and behaviour in code, including methods and inheritance. An ER diagram models stored data with tables, primary keys and foreign keys, and has no methods at all.

Database assignments usually want an ERD, while object-oriented design work wants a class diagram. The ER diagram generator on this site covers the data side, and both produce Draw.io files from the same description, which keeps names consistent.