Design-Pattern-MCP

An MCP (Model Context Protocol) server that provides design pattern structural constraints and anti-patterns to AI coding agents. Agents call this server during code generation to ensure they implement patterns correctly.

This server is not for human use. It is called by AI coding agents (Claude Code, Cursor, Copilot, etc.).

Tools

`suggest_pattern`

Map a problem description to pattern name(s).

Input: { description: string, category?: "creational"|"structural"|"behavioral"|"modern"|"architectural" }

Output: Up to 3 PatternSuggestion[] — { name, category, rationale, confidence }

Token cost: ~50–100 tokens

`get_template`

Get structural constraints and anti-patterns for a specific pattern in a specific language.

Input: { pattern: string, language: "go"|"java"|"python"|"rust"|"typescript"|"generic" }

Output: Compact plain text with COMPONENTS, CONSTRAINTS, ANTI-PATTERNS, language-specific notes, example structure

Token cost: ~300–500 tokens

Installation

git clone [email protected]:sirius-zuo/design-pattern-mcp.git
cd design-pattern-mcp
npm install
npm run build

Register with Claude Code

Add to ~/.claude/settings.json:

{
  "mcpServers": {
    "design-pattern-templates": {
      "command": "node",
      "args": ["/absolute/path/to/design-pattern-mcp/dist/index.js"]
    }
  }
}

Register with Cursor

Add to .cursor/mcp.json (project) or ~/.cursor/mcp.json (global):

{
  "mcpServers": {
    "design-pattern-templates": {
      "command": "node",
      "args": ["/absolute/path/to/design-pattern-mcp/dist/index.js"]
    }
  }
}

Register with Windsurf

Add to ~/.codeium/windsurf/mcp_config.json:

{
  "mcpServers": {
    "design-pattern-templates": {
      "command": "node",
      "args": ["/absolute/path/to/design-pattern-mcp/dist/index.js"]
    }
  }
}

Register with GitHub Copilot (VS Code)

Add to .vscode/mcp.json (project) or user settings:

{
  "servers": {
    "design-pattern-templates": {
      "type": "stdio",
      "command": "node",
      "args": ["/absolute/path/to/design-pattern-mcp/dist/index.js"]
    }
  }
}

Usage in Claude Desktop

Once registered, you can ask Claude to use the tools directly in conversation. The typical workflow is: suggest a pattern first, then fetch the full template for the one you want to implement.

Example 1 — Find the right pattern

You ask Claude:

I need to support multiple payment methods like credit card, PayPal, and crypto that can be swapped at runtime. What pattern should I use?

Claude calls suggest_pattern and returns:

[
  {
    "name": "Strategy",
    "category": "behavioral",
    "rationale": "multiple interchangeable algorithms",
    "confidence": 0.67
  },
  {
    "name": "Decorator",
    "category": "structural",
    "rationale": "add responsibilities dynamically without subclassing",
    "confidence": 0.50
  },
  {
    "name": "Saga",
    "category": "modern",
    "rationale": "long-running distributed transaction",
    "confidence": 0.33
  }
]

Strategy is the strongest match. You then ask for the full template.

Example 2 — Get the full template for your language

You ask Claude:

Give me the Strategy pattern template for TypeScript.

Claude calls get_template with { pattern: "strategy", language: "typescript" } and returns:

Pattern: Strategy
Language: typescript

COMPONENTS:
- **Context**: Holds a reference to a Strategy. Delegates algorithm execution to it. Contains NO algorithm logic itself.

CONSTRAINTS:
- Context must NOT contain algorithm logic; all logic lives in ConcreteStrategy.

ANTI-PATTERNS:
- Embedding the if/else or switch selection logic inside Context (defeats the purpose).

TYPESCRIPT-SPECIFIC NOTES:
- Define single-method stateless strategies as function types: `type SortStrategy = (data: number[]) => number[]` — no interface or class needed.
- Multi-method or stateful strategies: use an `interface` with structural typing — no `implements` declaration required.
- Inject via constructor (`constructor(private strategy: SortStrategy)`) for immutability; use a setter only when runtime switching is required.
- `Context` holds a field typed to the function type or interface; calling it is `this.strategy(params)` or `this.strategy.execute(params)`.

EXAMPLE STRUCTURE:
```typescript
type Sorter = (data: number[]) => number[];

class SortContext {
  constructor(private strategy: Sorter) {}
  setStrategy(s: Sorter): void { this.strategy = s; }
  run(data: number[]): number[] { return this.strategy(data); }
}

// Usage — any function with the right signature is a valid strategy
const ctx = new SortContext(data => [...data].sort((a, b) => a - b));
ctx.run([3, 1, 2]); // [1, 2, 3]

// Interface-based for stateful strategies
interface PricingStrategy { calculate(basePrice: number): number; }
class DiscountStrategy implements PricingStrategy {
  constructor(private pct: number) {}
  calculate(base: number): number { return base * (1 - this.pct); }
}

Claude then uses this output as grounding constraints when writing your actual payment service code — ensuring the context doesn't embed algorithm logic, strategies are injected via constructor, and the TypeScript-idiomatic function-type approach is used.

Pattern Coverage

38 patterns across 5 categories:

Creational (5): Abstract Factory, Builder, Factory Method, Prototype, Singleton
Structural (7): Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy
Behavioral (11): Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor
Modern (8): Circuit Breaker, CQRS, Dependency Injection, Event Sourcing, Pub/Sub, Repository, Retry with Backoff, Saga
Architectural (7): Clean Architecture, Event-Driven Architecture, Hexagonal Architecture, Layered Architecture, Microservices, MVC/MVP/MVVM, Pipe and Filter

Development

npm test         # run tests
npm run build    # compile TypeScript to dist/
npm start        # run the MCP server

Design-Pattern-MCP