software-architecture

What this skill does

# Software Architecture Documentation

Document system architecture using a root `ARCHITECTURE.md` with detailed component docs in `docs/*.md`.

## Structure

```
project/
├── ARCHITECTURE.md      # High-level system overview
└── docs/
    ├── <component>.md   # Detailed component documentation
    └── ...
```

## Proactive Usage

When `ARCHITECTURE.md` exists in project root:

1. **Before major changes**: Read `ARCHITECTURE.md` to understand system structure
2. **After structural changes**: Update diagrams and entry points
3. **When adding components**: Create new `docs/*.md` file and link from `ARCHITECTURE.md`
4. **During refactoring**: Update affected diagrams and file references

## Creating Architecture Documentation

### Initial Setup Workflow

1. **Analyze codebase structure**
   - Identify entry points (main, CLI, API handlers)
   - Map major components and their responsibilities
   - Trace key data flows

2. **Create `ARCHITECTURE.md`**
   - Write system overview (1-2 paragraphs)
   - Add C4 Context diagram showing system boundaries
   - Document entry points table
   - List key abstractions
   - Add testing overview
   - Link to detail docs (create `docs/` section even if empty initially)

3. **Create detail docs for major components**
   - One file per logical component in `docs/`
   - Name files to match component names (flexible convention)
   - Include component-level diagrams

See [references/document-templates.md](references/document-templates.md) for complete templates.

## ARCHITECTURE.md Sections

### Required Sections

| Section | Content |
|---------|---------|
| Overview | 1-2 paragraphs on system purpose |
| System Diagram | C4 Context or Container diagram |
| Key Entry Points | Table of primary files with descriptions |
| Key Abstractions | Table of important classes/interfaces/functions |
| Testing | Overview of test strategy and key test locations |
| Detail Docs | Links to `docs/*.md` files |

### Optional Sections

| Section | Include When |
|---------|--------------|
| Data Flow | Complex pipelines or transformations |
| Code Organization | Non-obvious directory structure |
| Configuration | Significant config or environment setup |

## Detail Documents (`docs/*.md`)

Create a detail doc when a component:
- Has 3+ key files or abstractions
- Contains complex internal logic
- Interacts with multiple other components
- Needs sequence diagrams to explain flows

### Naming Convention

Flexible. Match the component's identity:
- `docs/auth.md` for authentication component
- `docs/data-pipeline.md` for data pipeline
- `docs/cli.md` for CLI handling

### Required Content

| Section | Content |
|---------|---------|
| Purpose | What this component does |
| Key Files | Table of important files |
| Key Abstractions | Classes, interfaces, functions |

### Optional Content

| Section | Include When |
|---------|--------------|
| Architecture Diagram | Multiple internal subcomponents |
| Sequence Diagram | Multi-step interactions |
| Dependencies | Non-obvious dependencies |
| Testing | Component-specific test patterns |
| Configuration | Component-specific config |

## Diagram Selection

| Diagram Type | Use For |
|--------------|---------|
| C4 Context | `ARCHITECTURE.md` - system boundaries and external actors |
| C4 Container | `ARCHITECTURE.md` - deployable units (services, databases) |
| C4 Component | `docs/*.md` - internal structure of a component |
| Flowchart | Control flow, pipelines, decision logic |
| Sequence | Request flows, API interactions, multi-step processes |
| ER Diagram | Data models, entity relationships |
| Class Diagram | Object hierarchies, interface implementations |

Start minimal (3-5 nodes). Add detail only when it improves clarity.

See [references/mermaid-patterns.md](references/mermaid-patterns.md) for diagram templates.

## Entry Points and Abstractions

### Entry Points Table

Document files that serve as starting points for understanding the codebase:

```markdown
| File | Description |
|------|-------------|
| `src/main.py` | Application entry point |
| `src/core/engine.py` | Core processing engine |
| `tests/conftest.py` | Test fixtures and setup |
```

Include:
- Application entry points (main, CLI, handlers)
- Core domain logic locations
- Configuration files
- Test setup and fixtures

### Key Abstractions Table

Document important classes, interfaces, and functions:

```markdown
| Abstraction | Location | Purpose |
|-------------|----------|---------|
| `Engine` | `src/core/engine.py` | Orchestrates processing |
| `Handler` | `src/api/base.py` | Request handling interface |
```

Focus on:
- Base classes and interfaces
- Core domain objects
- Public API surfaces
- Extension points

## Maintaining Documentation

### When to Update

| Trigger | Action |
|---------|--------|
| New component added | Create `docs/<component>.md`, add link to `ARCHITECTURE.md` |
| Entry point changed | Update entry points table |
| Major refactoring | Update affected diagrams and file references |
| New external dependency | Update C4 Context diagram |
| Component removed | Remove or archive corresponding detail doc |

### Update Checklist

After structural changes:
1. Verify entry points table is accurate
2. Check diagram nodes match actual components
3. Confirm file paths in tables are valid
4. Update any affected detail docs