About Class Diagram Generator

Generate UML class diagrams with classes, attributes, methods, and relationships. Part of the DevTools Surf developer suite. Browse more tools in the Diagrams & Workflows collection.

Use Cases

• Visualize inheritance hierarchies and interface implementations in a codebase
• Generate UML diagrams from code for architecture documentation
• Review class design before implementation to catch coupling issues
• Produce diagrams for technical design documents and code reviews

Tips

• Paste class definitions or TypeScript interfaces — the parser extracts class names, attributes, methods, and basic inheritance
• Use the relationship panel to add associations, aggregations, compositions, and dependencies that aren't inferable from code alone
• Export as PlantUML or Mermaid text to embed the diagram source in your codebase as living documentation

Fun Facts

• The Unified Modeling Language (UML) was standardized by the Object Management Group (OMG) in 1997, consolidating three competing object-oriented design notations: Booch, OMT (Rumbaugh), and OOSE (Jacobson). The three creators became known as 'the Three Amigos.'
• Despite UML having 14 diagram types, surveys consistently find that only class diagrams and sequence diagrams are used regularly by working software engineers. The other 12 types are largely confined to academic and enterprise architecture contexts.
• Mermaid.js, a popular text-based diagramming tool that supports class diagrams, was created by Knut Sveidqvist in 2014. GitHub added native Mermaid rendering in 2022, making text-based diagrams a first-class part of repository documentation.

FAQ

What is the difference between association, aggregation, and composition?

Association is a general 'uses' relationship. Aggregation is 'has-a' where the child can exist independently (Department has Employees). Composition is a stronger 'owns' where the child cannot exist without the parent (Order has OrderItems). They differ in lifecycle dependency.

Should I write UML first or code first?

For small systems, code-first and generate UML for documentation. For complex systems with multiple teams, design the class structure in UML first to agree on interfaces before parallel implementation. Both approaches are valid depending on team size and system complexity.

Can the generator handle multiple inheritance?

Yes — the diagram shows multiple parent classes for a single child. Note that multiple inheritance of implementation (not just interface) is only supported in some languages (C++, Python). Java and TypeScript support only single class inheritance.