d2

name: d2 description: Generate diagrams using D2 (Terrastruct) -- a modern, clean diagram scripting language with excellent auto-layout. Use when the diagram-router selects D2, or when the user wants clean architecture diagrams, nested containers, or prefers D2's aesthetic. Requires the d2 CLI binary.

D2 Diagram Skill

Generate diagrams using D2's declarative syntax. D2 produces clean, modern-looking diagrams with excellent auto-layout, nested containers, and multiple layout engines.

When to use D2:

• Architecture diagrams with nested components (D2's container nesting is excellent)
• Clean, modern aesthetic without manual positioning
• User has d2 installed or prefers it
• Network/infrastructure diagrams
• Deployment diagrams with hierarchical grouping

When another format is better:

• Maximum visual customization (SVG)
• Diagrams in GitHub/GitLab markdown (Mermaid -- D2 doesn't render natively)
• Whiteboard/sketch aesthetic (Excalidraw)
• ER diagrams, Gantt charts (Mermaid has better support)

Consult the design-system skill for color, composition, and quality rules.

Syntax Quick Reference

Basic Connections

server -> database: query
database -> server: results
client -> server: HTTPS

Arrow types:

• -> directed (default)
• <-> bidirectional
• -- undirected

Shapes and Labels

# Named with label
api: API Gateway

# Shapes
db: Database {
  shape: cylinder
}
user: User {
  shape: person
}
decision: Route? {
  shape: diamond
}
queue: Messages {
  shape: queue
}

Available shapes: rectangle (default), square, page, parallelogram, document, cylinder, queue, package, step, callout, stored_data, person, diamond, oval, circle, hexagon, cloud.

Containers (Nested)

D2's killer feature -- nested containers for hierarchy:

aws: AWS {
  vpc: VPC {
    public: Public Subnet {
      alb: Load Balancer {
        shape: hexagon
      }
    }
    private: Private Subnet {
      app: App Server
      db: Database {
        shape: cylinder
      }
      app -> db: SQL
    }
    public.alb -> private.app: HTTP
  }
}

Sequence Diagrams

shape: sequence_diagram

client: Client
server: Server
db: Database

client -> server: POST /users
server -> db: INSERT INTO users
db -> server: OK
server -> client: 201 Created

SQL Tables

users: Users {
  shape: sql_table
  id: int {constraint: primary_key}
  name: varchar
  email: varchar {constraint: unique}
}

orders: Orders {
  shape: sql_table
  id: int {constraint: primary_key}
  user_id: int {constraint: foreign_key}
  total: decimal
}

users -> orders: has many

Classes

classes: {
  UserService: {
    shape: class
    +getUser(id): User
    +createUser(data): User
    -validateEmail(email): bool
  }
}

Styling

server: Server {
  style: {
    fill: "#EFF6FF"
    stroke: "#2563EB"
    border-radius: 8
    font-color: "#1E293B"
    shadow: true
  }
}

# Connection styling
server -> db: {
  style: {
    stroke: "#64748B"
    stroke-dash: 4
  }
}

Themes

D2 has built-in themes. Set at the top of the file:

vars: {
  d2-config: {
    theme-id: 200
  }
}

Theme IDs: 0 (default), 1 (neutral grey), 3 (flagship terrastruct), 4 (cool classics), 100 (mixed berry blue), 200 (grape soda), 300 (aubergine). Dark themes: 200-302.

Layout Engines

D2 supports multiple layout engines:

Set via CLI flag: d2 --layout elk diagram.d2 output.svg

Common Mistakes to Avoid

1. Undeclared connections -- reference nodes before connecting: define a: Label before a -> b
2. Missing colons -- labels need a colon: server: API Server not server API Server
3. Nested path separators -- use . for nested references: aws.vpc.app not aws/vpc/app
4. Forgetting shape -- containers don't need explicit shape; leaf nodes default to rectangle
5. Style outside element -- styles must be inside the element block: server: { style: { ... } }
6. Too deep nesting -- 3-4 levels max for readability

Output Format

Save as .d2 file. Render to SVG or PNG:

# Render to SVG
d2 diagram.d2 diagram.svg

# Render to PNG
d2 --format png diagram.d2 diagram.png

# Watch mode (live preview)
d2 --watch diagram.d2 diagram.svg

Setup Detection

Before generating D2, check if the user has it installed:

command -v d2 && d2 --version

If not installed, suggest:

# macOS
brew install d2

# Linux (script)
curl -fsSL https://d2lang.com/install.sh | sh -s --

# Go install
go install oss.terrastruct.com/d2@latest

Quality Checklist

Before presenting a D2 diagram:

• Connections reference defined nodes
• Container nesting is max 3-4 levels deep
• Labels are present on all connections that need explanation
• Shapes are semantically appropriate (cylinder for DB, person for user)
• Theme specified if not using default
• File saves with .d2 extension