Mermaid vs PlantUML: Which Diagram Syntax Should You Choose?

When it comes to creating diagrams online, two of the most popular text-based syntaxes are Mermaid and PlantUML. Both offer powerful diagramming capabilities, but they have different strengths and use cases. In this comprehensive comparison, we'll help you choose the right tool for your specific needs.

Overview: Mermaid vs PlantUML

Mermaid

• Created by: Knut Sveidqvist (now maintained by Mermaid.js team)
• First Release: 2014
• Syntax: Text-based, declarative
• Rendering: Client-side JavaScript (browser) or server-side (Node.js)
• Learning Curve: Easy to moderate
• Community: Very active and rapidly growing
• Latest Version: 11.x (as of 2025)

PlantUML

• Created by: Arnaud Roques
• First Release: 2009
• Syntax: Text-based, UML-inspired
• Rendering: Server-side (Java) or client-side (WebAssembly)
• Learning Curve: Moderate to steep
• Community: Mature, stable, and well-established
• Latest Version: 1.2025.x (actively maintained)

Syntax Comparison

Basic Flowchart Example

Mermaid Syntax:

graph TD
    A[Start] --> B{Decision?}
    B -->|Yes| C[Process A]
    B -->|No| D[Process B]
    C --> E[End]
    D --> E

PlantUML Syntax:

@startuml
start
:Decision?;
if (Yes?) then (yes)
  :Process A;
else (no)
  :Process B;
endif
stop
@enduml

Sequence Diagram Example

Mermaid Syntax:

sequenceDiagram
    participant U as User
    participant S as System
    participant D as Database

    U->>S: Login Request
    S->>D: Query User
    D-->>S: User Data
    S-->>U: Login Success

PlantUML Syntax:

@startuml
actor User
participant "System" as S
database "Database" as D

User -> S: Login Request
S -> D: Query User
D --> S: User Data
S --> User: Login Success
@enduml

Feature Comparison

Supported Diagram Types

| Diagram Type | Mermaid | PlantUML | | ------------------- | ------- | -------- | | Flowcharts | ✅ | ✅ | | Sequence Diagrams | ✅ | ✅ | | Class Diagrams | ✅ | ✅ | | Use Case Diagrams | ❌ | ✅ | | Activity Diagrams | ✅ | ✅ | | Component Diagrams | ❌ | ✅ | | Deployment Diagrams | ❌ | ✅ | | State Diagrams | ✅ | ✅ | | Timing Diagrams | ❌ | ✅ | | Entity Relationship | ✅ | ✅ | | User Journey | ✅ | ❌ | | Gantt Charts | ✅ | ✅ | | Pie Charts | ✅ | ❌ | | Git Graphs | ✅ | ❌ | | Mindmaps | ✅ | ✅ | | Timeline | ✅ | ❌ | | Quadrant Chart | ✅ | ❌ | | XY Chart | ✅ | ❌ | | Sankey Diagram | ✅ | ❌ | | Block Diagram | ✅ | ❌ | | Kanban | ✅ | ❌ | | Architecture | ✅ | ✅ | | C4 Diagram | ✅ | ✅ | | Network Diagram | ❌ | ✅ | | Salt (UI Mockups) | ❌ | ✅ | | Math Notation | ❌ | ✅ |

Syntax Complexity

Mermaid Pros:

• More intuitive and readable syntax
• Excellent for quick prototyping and documentation
• Native browser support with lightweight dependencies
• Wide variety of modern diagram types (Sankey, XY charts, etc.)
• Active development with frequent new features
• Better for agile and modern development workflows

Mermaid Cons:

• Limited traditional UML diagram support
• Less extensive styling and theming options
• Newer tool with evolving syntax

PlantUML Pros:

• Complete UML 2.0 specification support
• Mature tool with extensive documentation
• Powerful customization and styling options
• Better for formal software documentation
• Excellent IDE integration
• Supports complex enterprise diagrams

PlantUML Cons:

• Steeper learning curve
• More verbose syntax
• Requires Java runtime for server-side rendering
• Can be overwhelming for simple use cases

Use Case Recommendations

Choose Mermaid When:

1. You're New to Diagramming

   • Easier to learn and get started
   • More intuitive syntax
   • Better for simple flowcharts

2. You Need Quick Prototypes

   • Faster to create basic diagrams
   • Less verbose syntax
   • Good for brainstorming

3. You Work with Web Technologies

   • JavaScript-based
   • Easy to integrate into web apps
   • Good browser support

4. You Need Data Visualization

   • Built-in pie charts and graphs
   • Good for simple data representation
   • Quick to create

Choose PlantUML When:

1. You Need Complete UML Support

   • Full UML specification compliance
   • All UML diagram types supported
   • Enterprise-grade features

2. You're Working on Complex Systems

   • Better for large, complex diagrams
   • More powerful customization
   • Better for system architecture

3. You're in an Enterprise Environment

   • Mature tool with long history
   • Better documentation
   • More community resources

4. You Need Advanced Features

   • Custom styling and themes
   • Advanced layout options
   • Better for technical documentation

Performance Considerations

Mermaid

• Rendering: Client-side JavaScript (browser) or Node.js (server)
• Speed: Very fast for most diagram types
• Dependencies: Lightweight (~1MB minified)
• Browser Support: All modern browsers
• Mobile: Responsive and mobile-friendly
• Offline: Works offline once loaded

PlantUML

• Rendering: Server-side Java or client-side WebAssembly
• Speed: Fast but depends on server resources
• Dependencies: Java 8+ (server) or WebAssembly (client)
• Browser Support: Excellent with WASM renderer
• Mobile: Good support with responsive output
• Offline: Possible with local server or WASM

Integration and Tooling

Mermaid Integration

• GitHub: Native support in markdown (2022+)
• GitLab: Native support in markdown
• Notion: Native support
• Obsidian: Native support
• Confluence: Plugin available
• VS Code: Multiple excellent extensions
• JetBrains IDEs: Plugin support
• Jupyter Notebooks: Native support
• Docusaurus: Built-in support
• GitBook: Native support
• Web Apps: Easy to embed with CDN

PlantUML Integration

• IntelliJ IDEA: Excellent native plugin
• Eclipse: Official plugin
• VS Code: Multiple extensions available
• Confluence: Official plugin
• MediaWiki: Extension available
• Sphinx: Integration for documentation
• LaTeX: Integration available
• CI/CD: Docker images and CLI tools
• Enterprise Tools: Wide enterprise adoption
• Web Services: Online rendering services

Learning Resources

Mermaid Learning Path

1. Start with Flowcharts: Basic syntax and concepts
2. Move to Sequence Diagrams: Learn interaction patterns
3. Explore Class Diagrams: Understand object relationships
4. Advanced Features: Custom styling and themes

PlantUML Learning Path

1. Learn UML Basics: Understand UML concepts
2. Start with Use Cases: Simple actor-system interactions
3. Sequence Diagrams: Complex system interactions
4. Class Diagrams: Object-oriented modeling
5. Advanced UML: State machines, components, etc.

Real-World Examples

Example 1: Simple Process Flow

Mermaid (Recommended):

graph LR
    A[User Input] --> B[Validate]
    B --> C{Valid?}
    C -->|Yes| D[Process]
    C -->|No| E[Show Error]
    D --> F[Save]
    E --> A
    F --> G[Complete]

PlantUML (Alternative):

@startuml
start
:User Input;
:Validate;
if (Valid?) then (yes)
  :Process;
  :Save;
  :Complete;
else (no)
  :Show Error;
  stop
endif
stop
@enduml

Example 2: Complex System Architecture

PlantUML (Recommended):

@startuml
package "Frontend" {
  [React App]
  [User Interface]
}

package "Backend" {
  [API Gateway]
  [Authentication Service]
  [Data Service]
}

database "Database" {
  [User Data]
  [Application Data]
}

[React App] --> [API Gateway]
[API Gateway] --> [Authentication Service]
[API Gateway] --> [Data Service]
[Authentication Service] --> [User Data]
[Data Service] --> [Application Data]
@enduml

Best Practices for Each Tool

Mermaid Best Practices

• Keep diagrams simple and focused
• Use consistent naming conventions
• Leverage themes for styling
• Break complex diagrams into smaller parts
• Use comments for clarity

PlantUML Best Practices

• Follow UML conventions strictly
• Use proper UML notation
• Leverage packages for organization
• Use stereotypes for customization
• Maintain consistent styling

Conclusion

The choice between Mermaid and PlantUML depends on your specific needs:

Choose Mermaid if:

• You're new to diagramming
• You need quick, simple diagrams
• You work primarily with web technologies
• You need data visualization features

Choose PlantUML if:

• You need complete UML support
• You're working on complex systems
• You're in an enterprise environment
• You need advanced customization

Hybrid Approach

Many teams use both tools:

• Mermaid for quick prototypes and simple diagrams
• PlantUML for formal documentation and complex UML diagrams

This approach gives you the best of both worlds - the simplicity of Mermaid for everyday use and the power of PlantUML for complex system modeling.

Getting Started

Ready to try both? Visit EveryDiagram to experiment with both Mermaid and PlantUML syntaxes. You can easily switch between them and see the results in real-time.

Remember, the best tool is the one that helps you communicate your ideas most effectively. Start simple, experiment with both, and choose the syntax that works best for your specific use case.