flowchart TD
    A[Start] --> B{Decision?}
    B -->|Yes| C[Action 1]
    B -->|No| D[Action 2]
    C --> E[End]
    D --> E

sequenceDiagram
    participant U as User
    participant A as App
    participant S as Server
    participant D as Database
    
    U->>A: Click Login
    A->>S: POST /auth/login
    S->>D: Query user
    D-->>S: User data
    S-->>A: JWT token
    A-->>U: Redirect to dashboard

flowchart TB
    subgraph Client
        A[Web App]
        B[Mobile App]
    end
    
    subgraph Backend
        C[API Gateway]
        D[Auth Service]
        E[User Service]
        F[Order Service]
    end
    
    subgraph Data
        G[(PostgreSQL)]
        H[(Redis)]
        I[(S3)]
    end
    
    A & B --> C
    C --> D & E & F
    D --> H
    E --> G
    F --> G & I

erDiagram
    CUSTOMER ||--o{ ORDER : places
    ORDER ||--|{ LINE_ITEM : contains
    PRODUCT ||--o{ LINE_ITEM : "ordered in"
    
    CUSTOMER {
        int id PK
        string name
        string email
    }
    ORDER {
        int id PK
        date created_at
        int customer_id FK
    }
    PRODUCT {
        int id PK
        string name
        decimal price
    }

classDiagram
    class Animal {
        +String name
        +int age
        +makeSound()
    }
    class Dog {
        +String breed
        +bark()
    }
    class Cat {
        +boolean indoor
        +meow()
    }
    
    Animal <|-- Dog
    Animal <|-- Cat

stateDiagram-v2
    [*] --> Draft
    Draft --> Submitted: Submit
    Submitted --> InReview: Assign reviewer
    InReview --> Approved: Approve
    InReview --> Rejected: Reject
    Rejected --> Draft: Revise
    Approved --> [*]

gantt
    title Project Timeline
    dateFormat  YYYY-MM-DD
    
    section Planning
    Requirements    :a1, 2024-01-01, 14d
    Design          :a2, after a1, 21d
    
    section Development
    Backend         :b1, after a2, 30d
    Frontend        :b2, after a2, 30d
    
    section Testing
    QA Testing      :c1, after b1, 14d
    UAT             :c2, after c1, 7d

mindmap
    root((Project))
        Features
            Feature A
            Feature B
            Feature C
        Team
            Frontend
            Backend
            Design
        Timeline
            Q1
            Q2
            Q3

gitGraph
    commit
    commit
    branch feature
    checkout feature
    commit
    commit
    checkout main
    merge feature
    commit

# Diagram: [Name]

**Type**: [Flowchart / Sequence / Architecture / etc.]
**Tool**: [Mermaid / PlantUML]
**Purpose**: [What it illustrates]

---

## Diagram Code

### Mermaid

```mermaid
[Mermaid code here]

[PlantUML code here]

%%{init: {'theme':'forest'}}%%

---

## PlantUML Examples

### Sequence Diagram
```plantuml
@startuml
actor User
participant "Web App" as App
participant "API Server" as API
database "Database" as DB

User -> App: Login request
App -> API: POST /auth/login
API -> DB: SELECT user
DB --> API: User record
API --> App: JWT token
App --> User: Redirect to dashboard
@enduml

@startuml
package "Frontend" {
    [React App]
    [Mobile App]
}

package "Backend" {
    [API Gateway]
    [Auth Service]
    [User Service]
}

database "PostgreSQL" as DB

[React App] --> [API Gateway]
[Mobile App] --> [API Gateway]
[API Gateway] --> [Auth Service]
[API Gateway] --> [User Service]
[User Service] --> DB
@enduml