# Architecture Patterns

> Common software architecture patterns, ADR templates, and anti-pattern detection. Supports architectural review, design decisions, and system documentation.

- Skill: `groupzer0/architecture-patterns` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add groupzer0/architecture-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/groupzer0/architecture-patterns/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Docs & Writing
- License: MIT
- Author: groupzer0 (https://skillmd.com/u/groupzer0)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/groupzer0/architecture-patterns

---


# Architecture Patterns

Reference for architectural design and documentation. Use this skill when:
- Architect reviews system design
- Planner considers architectural constraints
- Analyst investigates integration approaches
- Critic evaluates architectural alignment

## Architecture Decision Records (ADR)

### ADR Format

Every significant architectural decision should be documented:

```markdown
# ADR-[NNN]: [Decision Title]

## Status
[Proposed | Accepted | Deprecated | Superseded by ADR-XXX]

## Context
[What is the situation? What forces are at play?]

## Decision
[What is the change being proposed or decided?]

## Consequences
### Positive
- [Benefit 1]
- [Benefit 2]

### Negative
- [Tradeoff 1]
- [Tradeoff 2]

### Neutral
- [Side effect]

## Alternatives Considered
1. [Alternative 1]: [Why rejected]
2. [Alternative 2]: [Why rejected]

## Related
- ADR-XXX: [Related decision]
- [External reference]
```

### When to Write ADRs

| Scenario | ADR Required? |
|----------|--------------|
| New external dependency | Yes |
| New architectural pattern | Yes |
| Technology switch | Yes |
| Module boundary change | Yes |
| Performance tradeoff | Yes |
| Bug fix | No |
| Refactoring (same behavior) | Usually no |

---

## Common Patterns

### Layered Architecture

```
┌─────────────────────────────────┐
│         Presentation            │  UI, API endpoints
├─────────────────────────────────┤
│          Application            │  Use cases, orchestration
├─────────────────────────────────┤
│           Domain                │  Business logic, entities
├─────────────────────────────────┤
│        Infrastructure           │  DB, external services
└─────────────────────────────────┘
```

**Rules:**
- Dependencies point downward only
- Lower layers never import from higher
- Domain has no external dependencies

**Use when:** Enterprise apps, clear separation needed

### Repository Pattern

**Purpose:** Abstract data access, enable testability

```typescript
// Interface in domain layer
interface UserRepository {
  findById(id: string): Promise<User | null>;
  save(user: User): Promise<void>;
}

// Implementation in infrastructure layer
class PostgresUserRepository implements UserRepository {
  async findById(id: string): Promise<User | null> {
    const row = await db.query('SELECT * FROM users WHERE id = $1', [id]);
    return row ? mapToUser(row) : null;
  }
}
```

**Use when:** 
- Need to swap data stores
- Testing without real database
- Multiple data sources

### Service Layer

**Purpose:** Encapsulate business operations

```typescript
class OrderService {
  constructor(
    private orderRepo: OrderRepository,
    private paymentGateway: PaymentGateway,
    private notifier: Notifier
  ) {}

  async placeOrder(cart: Cart, payment: PaymentInfo): Promise<Order> {
    const order = Order.fromCart(cart);
    await this.paymentGateway.charge(payment, order.total);
    await this.orderRepo.save(order);
    await this.notifier.sendConfirmation(order);
    return order;
  }
}
```

**Use when:**
- Multiple steps in operation
- Transaction coordination
- Cross-cutting concerns

### Event-Driven Architecture

```
┌─────────┐    Event    ┌─────────┐
│ Service │───────────► │  Queue  │
│    A    │             │         │
└─────────┘             └────┬────┘
                             │
              ┌──────────────┼──────────────┐
              ▼              ▼              ▼
         ┌─────────┐   ┌─────────┐   ┌─────────┐
         │ Handler │   │ Handler │   │ Handler │
         │    1    │   │    2    │   │    3    │
         └─────────┘   └─────────┘   └─────────┘
```

**Use when:**
- Loose coupling between components
- Asynchronous processing
- Multiple consumers of same event
- Audit trail needed

### Dependency Injection

**Purpose:** Invert control, enable testing

```typescript
// Without DI (hard to test)
class OrderService {
  private db = new PostgresDatabase();
}

// With DI (testable)
class OrderService {
  constructor(private db: Database) {}
}

// Production
new OrderService(new PostgresDatabase());

// Test
new OrderService(new MockDatabase());
```

---

## Anti-Patterns to Detect

| Anti-Pattern | Detection | Fix |
|--------------|-----------|-----|
| **God Object** | Class with 20+ methods, 500+ lines | Extract classes |
| **Circular Dependencies** | A→B→C→A | Introduce interface |
| **Big Ball of Mud** | No clear structure | Define boundaries |
| **Spaghetti Code** | Tangled control flow | Refactor, add layers |
| **Golden Hammer** | Same pattern everywhere | Choose appropriate |
| **Anemic Domain** | Data classes + procedure classes | Move logic to domain |
| **Leaky Abstraction** | Implementation details exposed | Hide behind interface |
| **Premature Optimization** | Complex code for speed | Measure first |

### Detection Commands

```bash
# Find large files (potential God objects)
find . -name "*.ts" -exec wc -l {} \; | sort -rn | head -10

# Find circular dependencies (TypeScript)
npx madge --circular src/

# Find files with many imports
grep -c "^import" src/**/*.ts | sort -t: -k2 -rn | head -10
```

---

## System Architecture Documentation

### Required Sections

For `system-architecture.md`:

1. **Purpose**: What does this system do?
2. **High-Level Architecture**: Diagram, major components
3. **Components**: Each component's responsibility
4. **Data Flow**: How data moves through system
5. **Dependencies**: External services, libraries
6. **Quality Attributes**: Performance, security, scalability goals
7. **Decisions**: ADRs or decision log
8. **Known Issues**: Technical debt, problem areas

### Diagram Standards

Use Mermaid for version-controlled diagrams:

```mermaid
graph TB
    subgraph Presentation
        API[API Gateway]
        UI[Web UI]
    end
    
    subgraph Application
        Auth[Auth Service]
        Orders[Order Service]
    end
    
    subgraph Data
        DB[(PostgreSQL)]
        Cache[(Redis)]
    end
    
    UI --> API
    API --> Auth
    API --> Orders
    Orders --> DB
    Orders --> Cache
```

---

## Reconciliation Changelog Template

When the Architect reconciles architecture docs after implementations, use this format in the `system-architecture.md` changelog:

```markdown
| Date | Change | Rationale | Source |
|------|--------|-----------|--------|
| 2024-12-20 | Added memory retrieval caching layer | Reconciled from Plan-015 implementation | Plan-015-memory-caching |
| 2024-12-18 | Updated API boundary diagram | Implementation added new endpoint | Post-implementation audit |
| 2024-12-15 | Documented Cognee integration pattern | Previously undocumented, discovered during health audit | Health audit |
```

**Reconciliation Entry Format:**
- **Date**: When reconciliation occurred
- **Change**: What was updated in architecture docs
- **Rationale**: "Reconciled from Plan-NNN" or "Post-implementation audit" or "Health audit discovery"
- **Source**: Reference to plan, implementation, or audit that triggered reconciliation

---

## Design Debt Registry Template

Track architectural improvements in the **Problem Areas** section of `system-architecture.md`:

```markdown
## Problem Areas / Design Debt Registry

### Active Design Debt

| ID | Area | Current State | Optimal State | Priority | Discovered | Last Reviewed |
|----|------|---------------|---------------|----------|------------|---------------|
| DD-001 | Memory Subsystem | Direct Cognee calls scattered | Unified memory service facade | Medium | 2024-12-15 | 2024-12-20 |
| DD-002 | Error Handling | Inconsistent error types | Typed error hierarchy | Low | 2024-12-18 | 2024-12-18 |

### Resolved Design Debt

| ID | Resolution | Resolved Date | Related Plan |
|----|------------|---------------|--------------|
| DD-000 | Extracted shared utilities | 2024-12-10 | Plan-012 |
```

**Design Debt Entry Fields:**
- **ID**: Sequential identifier (DD-NNN)
- **Area**: Component or subsystem affected
- **Current State**: What exists now (brief)
- **Optimal State**: What would be better (brief)
- **Priority**: Critical / High / Medium / Low
- **Discovered**: When architect identified the debt
- **Last Reviewed**: When last evaluated (may affect priority)

**Priority Guidelines:**
- **Critical**: Blocking other improvements or causing active issues
- **High**: Should address in next 1-2 releases
- **Medium**: Address when touching related code
- **Low**: Nice-to-have, address opportunistically

---

## Agent Responsibilities

### Architect Agent
- Maintain `system-architecture.md` as single source of truth
- Document ADRs within master doc
- Challenge plans violating architectural constraints
- Provide verdicts: APPROVED / APPROVED_WITH_CHANGES / REJECTED

### Analyst Agent
- Reference architecture when investigating integration points
- Consult Architect for systemic pattern questions
- Document architectural context in analysis findings

### Planner Agent
- Read `system-architecture.md` before planning
- Ensure plans respect documented patterns
- Flag architectural impact in plan scope

### Critic Agent
- Reference `system-architecture.md` during plan review
- Verify architectural alignment
- Flag plans that violate documented decisions

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