🧩 Mermaid

Class diagram

Model your domain and object structure

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What is a Class diagram?

A class diagram describes the types in a system — their attributes, methods and relationships: inheritance, composition, association. It is the UML classic for domain modeling and code design.

Live example

Mermaid code

classDiagram
    class Order {
      +String id
      +Date createdAt
      +total() Money
    }
    class Customer {
      +String name
      +String email
    }
    class OrderLine {
      +int quantity
    }
    Customer "1" --> "*" Order
    Order "1" *-- "*" OrderLine

Live example

When to use it

Model a domain before writing code (DDD, OOP design)

Document existing codebases for onboarding

Design database object mappings and API resource models

Basic syntax

.mmd

classDiagram
    class Animal {
      +String name
      +makeSound() void
    }
    Animal <|-- Dog : inheritance

Questions about this diagram

Which relationships does Mermaid support?

Inheritance (<|--), composition (*--), aggregation (o--), association (-->), dependency (..>) and realization (..|>), each with optional cardinalities and labels.

Can I generate a class diagram from code?

Paste your classes or describe your domain and the AI extracts entities, attributes and relationships into a clean class diagram.

Explore other diagram types

🔀 Flowchart 💬 Sequence diagram 🗄️ Entity-relationship diagram 🔄 State diagram 📅 Gantt chart 🥧 Pie chart 🧠 Mind map 🌿 Git graph 🕰️ Timeline 🚶 User journey 🎯 Quadrant chart

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