c4-architecture - SKILL.md Agent Skill

name: c4-architecture description: > This skill should be used when the user asks to "create a C4 model", "generate architecture diagrams", "create a Structurizr workspace", "analyse the architecture", "model the system architecture", "create a system context diagram", "create a container diagram", "create a component diagram", "generate C4 diagrams", mentions C4, Structurizr, or architecture modelling, or needs to visualise software architecture. version: 0.1.0 tools: Read, Glob, Grep, Bash, Write, Edit

C4 Architecture Modelling with Structurizr DSL

Generate C4 architecture models using the Structurizr DSL and optionally render them as images.

When To Use

User wants to analyse and document software architecture
User asks for C4 diagrams (System Context, Container, Component, Deployment)
User wants to generate or update a Structurizr DSL workspace file
User wants to render architecture diagrams as images

Architecture Analysis Process

Step 1: Discover the System

Analyse the codebase to identify architectural elements:

Configuration & Build Files

package.json, pom.xml, build.gradle, go.mod, Cargo.toml, requirements.txt
docker-compose.yml, Dockerfile, kubernetes/*.yml
.env, configuration files, infrastructure-as-code

Identify Elements

People/Actors: Who uses the system? (end users, admins, external services)
Software Systems: The system being modelled + external systems it interacts with
Containers: Deployable units (web apps, APIs, databases, message queues, file stores)
Components: Logical groupings within containers (controllers, services, repositories)

Map Relationships

API calls between services (REST, gRPC, GraphQL)
Database connections and which containers access which stores
Message queue producers/consumers
External integrations (payment providers, email services, auth providers)
User interactions with the system

Step 2: Generate the Structurizr DSL

Write a workspace.dsl file following the Structurizr DSL syntax.

For the full DSL language reference, read: references/structurizr-dsl-reference.md For a working example, read: examples/example-workspace.dsl

Structure the workspace as follows:

workspace "[System Name]" "[Brief description]" {
    model {
        // 1. Define people (actors)
        // 2. Define software systems
        //    - Nest containers inside the primary system
        //    - Nest components inside containers (if needed)
        // 3. Define relationships between elements
    }
    views {
        // 4. Create views at each required C4 level
        // 5. Apply styling via themes or element/relationship styles
    }
}

Naming Conventions:

Use camelCase for identifiers: webApp, apiGateway, userDb
Use descriptive display names: "Web Application", "API Gateway"
Include technology labels: "Spring Boot REST API", "PostgreSQL 15"

Relationship Guidelines:

Always include a description: user -> webApp "Browses products using" "HTTPS"
Include technology where relevant: "REST/JSON", "JDBC", "AMQP"
Direction matters: source -> destination (who initiates the interaction)

Step 3: Create Views

Generate appropriate views based on the level of detail needed:

System Landscape: Overview of all systems (systemLandscape)
System Context: One system + its direct interactions (systemContext)
Container: Internal structure of a system (container)
Component: Internal structure of a container (component)
Deployment: Infrastructure mapping (deployment)

Always use autoLayout unless the user provides explicit layout preferences.

Step 4: Apply Styling

Use tags and styles to make diagrams readable:

styles {
    element "Person" {
        shape Person
        background #08427B
        color #ffffff
    }
    element "Software System" {
        background #1168BD
        color #ffffff
    }
    element "Container" {
        background #438DD5
        color #ffffff
    }
    element "Component" {
        background #85BBF0
        color #000000
    }
    element "Database" {
        shape Cylinder
    }
    element "External" {
        background #999999
        color #ffffff
    }
}

Step 5: Export and Render Diagrams

All export and rendering is done via Docker. Requires Docker to be installed and running.

Export DSL to C4-PlantUML:

mkdir -p ./diagrams
docker run --rm -v $PWD:/usr/local/structurizr structurizr/structurizr \
    export -workspace /usr/local/structurizr/workspace.dsl -format plantuml/c4plantuml -output /usr/local/structurizr/diagrams

Render PlantUML to PNG:

docker run --rm -v $PWD/diagrams:/data plantuml/plantuml -tpng /data/*.puml

Render PlantUML to SVG:

docker run --rm -v $PWD/diagrams:/data plantuml/plantuml -tsvg /data/*.puml

Other supported export formats: plantuml, mermaid, json.

Prerequisite: Docker (docker pull structurizr/structurizr && docker pull plantuml/plantuml)

Quality Checklist

Before presenting the workspace to the user, verify:

All identified systems, containers, and components are modelled
Every element has a description and technology label where appropriate
Relationships have meaningful descriptions (not just "uses")
External systems are clearly distinguished (tagged as "External")
Database elements use the Cylinder shape
Views exist for each appropriate C4 level
autoLayout is applied to all views
Styling is consistent and follows C4 colour conventions