PlantUML Ascii

A skill that generates PlantUML diagrams as ASCII art, producing text-based sequence diagrams, class diagrams, and architecture diagrams viewable in any terminal.

What Is This?

Overview

This skill creates PlantUML diagram definitions and renders them as ASCII art output. It covers sequence diagrams, class diagrams, activity diagrams, component diagrams, and state machines, all output as plain text that displays correctly in terminals, code comments, and documentation files.

Who Should Use This

Perfect for developers documenting architecture in code repositories, teams working in terminal-heavy environments, technical writers creating diagrams for plain text docs, and anyone needing diagrams without graphical rendering tools.

Why Use It?

Problems It Solves

Graphical diagrams require specialized tools and don't render in terminals, code reviews, or plain text files. ASCII diagrams created manually are tedious and hard to maintain. PlantUML with ASCII output generates professional diagrams from simple text definitions that version control tracks cleanly.

Core Highlights

• Text-Based Output - Diagrams render as ASCII art in any monospace font
• Multiple Diagram Types - Sequence, class, activity, component, and state diagrams
• Version Control Friendly - Plain text source that diffs and merges cleanly
• No GUI Required - Create and view diagrams entirely in the terminal
• Maintainable Source - Simple markup language that non-designers can edit

How to Use It?

Basic Usage

Ask Claude to create a PlantUML diagram, and this skill generates both the source and ASCII output.

Scenario 1: Sequence Diagram

Ask Claude: "Create a sequence diagram for user authentication"

Claude will generate:

@startuml
Client -> AuthService: POST /login (credentials)
AuthService -> Database: validate user
Database --> AuthService: user record
AuthService -> TokenService: generate JWT
TokenService --> AuthService: access token
AuthService --> Client: 200 OK (token)

Client -> API: GET /data (Bearer token)
API -> TokenService: verify token
TokenService --> API: valid claims
API -> Database: fetch data
Database --> API: results
API --> Client: 200 OK (data)
@enduml

Scenario 2: Component Architecture

Tell Claude: "Draw a microservices architecture diagram"

Claude will create:

@startuml
package "Frontend" {
  [Web App] as web
  [Mobile App] as mobile
}

package "API Gateway" {
  [Kong Gateway] as gateway
}

package "Services" {
  [User Service] as users
  [Order Service] as orders
  [Payment Service] as payments
  [Notification Service] as notify
}

package "Data" {
  database "PostgreSQL" as pg
  database "Redis" as redis
  queue "RabbitMQ" as mq
}

web --> gateway
mobile --> gateway
gateway --> users
gateway --> orders
gateway --> payments
orders --> mq
mq --> notify
users --> pg
orders --> pg
payments --> redis
@enduml

Real-World Examples

Architecture Decision Records

A development team included PlantUML diagrams in their ADR markdown files. ASCII rendering meant diagrams displayed correctly in GitHub pull request reviews without external rendering.

API Documentation

A backend team documented API flows with PlantUML sequence diagrams embedded in README files. New developers understood request flows without needing a separate documentation tool.

Advanced Tips

Diagram Themes

Apply PlantUML themes to control ASCII output density. Use skinparam monochrome true for cleaner ASCII rendering optimized for terminal display.

Automation in CI

Generate diagrams automatically in CI pipelines. PlantUML CLI renders diagrams from source files, ensuring documentation stays synchronized with code changes.

When to Use It?

Use Cases

• Code Documentation - Embed architecture diagrams in README and docs
• Code Review - Include diagrams in PR descriptions for context
• Terminal Workflows - View diagrams without leaving the command line
• Architecture Records - Document design decisions with visual context
• API Documentation - Illustrate request flows and data models

Related Topics

When you ask Claude these questions, this skill will activate:

• "Create a PlantUML sequence diagram"
• "Generate ASCII architecture diagram"
• "Draw a class diagram in text"
• "PlantUML component diagram"

Important Notes

Requirements

• PlantUML CLI or server for rendering (optional for source-only output)
• Java runtime for local PlantUML rendering
• Monospace font for proper ASCII art display
• Text editor with PlantUML preview support (optional)

Usage Recommendations

Do:

• Keep diagrams focused - One concept per diagram for clarity
• Use meaningful names - Label components and actors descriptively
• Version control sources - Store .puml files alongside code
• Add diagram titles - Include context with title and caption directives

Don't:

• Don't overcrowd diagrams - Split complex systems into multiple views
• Don't skip labels - Unlabeled arrows create ambiguous diagrams
• Don't embed in binary formats - Keep diagrams as text for diffability

Limitations

• ASCII rendering has lower fidelity than graphical output
• Complex diagrams with many connections become hard to read in ASCII
• Some diagram types render better than others in text mode
• Terminal width limits diagram horizontal complexity