Arch Lens C4 Container

C4 Container Architecture Lens

Cognitive Mode: Anatomical Primary Question: "How is it built?" Focus: Static Structure, Containers, Technology Choices, External Integrations

When to Use

• Need to understand the high-level technical building blocks
• Documenting container boundaries and communication
• Onboarding new team members to system architecture
• User invokes /autoskillit:arch-lens-c4-container or /autoskillit:make-arch-diag c4

Critical Constraints

NEVER:

• Modify any source code files
• Include internal implementation details (that's for other lenses)
• Show runtime behavior or state transitions
• Run subagents in the background (run_in_background: true is prohibited)

ALWAYS:

• Focus on CONTAINERS (deployable units, not classes)
• Show technology choices for each container
• Identify external systems and integrations
• BEFORE creating any diagram, LOAD the /autoskillit:mermaid skill using the Skill tool - this is MANDATORY
• If the Skill tool cannot be used (disable-model-invocation) or refuses this invocation, do NOT proceed with diagram creation. Abort this step and omit the diagram from output.
• After writing the diagram file, emit the absolute path as a structured output

token as your final output. Resolve the relative temp/arch-lens-c4-container/... save path to absolute by prepending the full CWD: `` diagram_path = /absolute/cwd/temp/arch-lens-c4-container/{filename}.md `` This token is MANDATORY — the pipeline cannot proceed without it.

Arguments

/autoskillit:arch-lens-c4-container [context_path]

• context_path (optional) — Absolute path to a PR context file containing new files

(★-prefixed) and modified files (●-prefixed) from the PR diff. When provided, read this file before beginning analysis and focus the diagram on the architectural areas affected by these specific files. When absent, explore the full CWD.

---

Analysis Workflow

Step 0: Read PR context (when provided)

If a context_path positional argument is present:

1. Read the file at context_path
2. Extract: new files list (★-prefixed), modified files list (●-prefixed)
3. Focus Step 1 exploration on the modules/components these files belong to
4. Apply ★ prefix on diagram nodes representing new files/components
5. Apply ● prefix on diagram nodes representing modified files/components

If no context_path is provided, skip this step and explore the full CWD in Step 1.

Step 1: Launch Parallel Exploration Subagents

Spawn Explore subagents to investigate:

Application Layer

• Find CLI entry points and commands
• Identify web applications and APIs
• Determine frontend technologies
• Look for: entry points, main files, CLI commands, app servers

Service/Business Logic Layer

• Find core business logic containers
• Identify processing engines or workflows
• Look for: services, core modules, domain logic, handlers

Package/Library Layer

• Find shared packages and utilities
• Identify internal libraries
• Look for: shared modules, utilities, common code, SDKs

Data Storage Layer

• Find database connections and storage
• Identify caching layers
• Look for: database configs, ORM models, repositories, cache clients

External Integrations

• Find API clients and external calls
• Identify third-party services
• Look for: HTTP clients, SDK imports, external API calls

Step 2: Identify Containers

For each container discovered, document:

• Name: Short descriptive name
• Technology: Primary technology/framework
• Responsibility: 2-3 word description
• Communication: How it talks to other containers

Step 3: Map Relationships

Identify connections between containers:

• Which containers call which?
• What protocols are used (HTTP, subprocess, import)?
• Which are synchronous vs asynchronous?

CRITICAL - Analyze Read/Write Direction: For EVERY component and connection, determine:

• Read sources: Where does this component READ data FROM?
• Write destinations: Where does this component WRITE data TO?
• Bidirectional: Does data flow both ways?

Label connections with direction:

• --> with "reads" or "queries" for read operations
• --> with "writes" or "saves" for write operations
• `` for bidirectional

Do NOT place write-only artifacts under "state tracking" or "source of truth" categories.

Step 4: Create the Diagram

Use the mermaid skill conventions to create a diagram with:

Direction: TB (top-to-bottom) for hierarchical container layout

Subgraphs for Layers:

• Application Layer (user-facing)
• Service Layer (business logic)
• Package Layer (shared utilities)
• Storage Layer (persistence)
• External Systems (third-party)

Node Styling:

• cli class: CLI, user interfaces, entry points
• phase class: Services, core processing
• handler class: Packages, shared utilities
• stateNode class: Databases, storage
• integration class: External APIs, third-party services

Connections:

• Solid arrows for primary data flow
• Label connections with action verbs

Step 5: Write Output

Write the diagram to: {{AUTOSKILLIT_TEMP}}/arch-lens-c4-container/arch_diag_c4_container_{YYYY-MM-DD_HHMMSS}.md (relative to the current working directory)

After writing the diagram file, emit a structured output line:

> IMPORTANT: Emit the structured output tokens as literal plain text with no > markdown formatting on the token names. Do not wrap token names in **bold**, > *italic*, or any other markdown. The adjudicator performs a regex match on the > exact token name — decorators cause match failure.

diagram_path = {absolute_path_to_diagram_file}

---

Output Template

# C4 Container Diagram: {Project Name}

**Lens:** C4 Container (Anatomical)
**Question:** How is it built?
**Date:** {YYYY-MM-DD}
**Scope:** {What was analyzed}

## Container Overview

| Container | Technology | Responsibility |
|-----------|------------|----------------|
| {name} | {tech} | {responsibility} |

## Architecture Diagram

```mermaid
%%{init: {'flowchart': {'nodeSpacing': 50, 'rankSpacing': 60, 'curve': 'basis'}}}%%
graph TB
    %% CLASS DEFINITIONS %%
    classDef cli fill:#1a237e,stroke:#7986cb,stroke-width:2px,color:#fff;
    classDef stateNode fill:#004d40,stroke:#4db6ac,stroke-width:2px,color:#fff;
    classDef handler fill:#e65100,stroke:#ffb74d,stroke-width:2px,color:#fff;
    classDef phase fill:#6a1b9a,stroke:#ba68c8,stroke-width:2px,color:#fff;
    classDef output fill:#00695c,stroke:#4db6ac,stroke-width:2px,color:#fff;
    classDef integration fill:#c62828,stroke:#ef9a9a,stroke-width:2px,color:#fff;

    %% USER %%
    USER(["User━━━━━━━━━━Role description"])

    subgraph Apps ["Application Layer"]
        direction TB
        APP1["Container Name━━━━━━━━━━TechnologyResponsibility"]
    end

    subgraph Services ["Service Layer"]
        direction TB
        SVC1["Container Name━━━━━━━━━━TechnologyResponsibility"]
    end

    subgraph Packages ["Shared Packages"]
        direction TB
        PKG1["Package Name━━━━━━━━━━TechnologyResponsibility"]
    end

    subgraph Storage ["Data Storage"]
        direction TB
        DB1[("Database━━━━━━━━━━TechnologyPurpose")]
    end

    subgraph External ["External Systems"]
        direction TB
        EXT1["External Service━━━━━━━━━━ProtocolPurpose"]
    end

    %% CONNECTIONS %%
    USER --> APP1
    APP1 --> SVC1
    SVC1 --> PKG1
    SVC1 --> DB1
    SVC1 --> EXT1

    %% CLASS ASSIGNMENTS %%
    class USER cli;
    class APP1 cli;
    class SVC1 phase;
    class PKG1 handler;
    class DB1 stateNode;
    class EXT1 integration;

Color Legend: | Color | Category | Description | |-------|----------|-------------| | Dark Blue | CLI/Apps | User-facing applications and entry points | | Purple | Services | Core business logic and services | | Orange | Packages | Shared utilities and libraries | | Teal | Storage | Database persistence layers | | Red | External | External integrations and APIs |

Key Architectural Insights

| Container | Responsibility | Technology | |-----------|---------------|------------| | {container} | {what it does} | {tech stack} |

Communication Patterns

• {Description of key communication patterns}

---

## Pre-Diagram Checklist

Before creating the diagram, verify:

- [ ] LOADED `/autoskillit:mermaid` skill using the Skill tool
- [ ] Using ONLY classDef styles from the mermaid skill (no invented colors)
- [ ] Diagram will include a color legend table

---

## Related Skills

- `/autoskillit:make-arch-diag` - Parent skill for lens selection
- `/autoskillit:mermaid` - MUST BE LOADED before creating diagram
- `/autoskillit:arch-lens-module-dependency` - For detailed coupling analysis
- `/autoskillit:arch-lens-deployment` - For physical deployment topology

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [TalonT-Org](https://github.com/TalonT-Org)
- **Source:** [TalonT-Org/AutoSkillit](https://github.com/TalonT-Org/AutoSkillit)
- **License:** MIT

Install and usage instructions live in the source repository linked above.