Design Patterns MCP Server

Instructions

Implementation Reference

• src/mcp-server.ts:321-351 (handler)

  Main execution handler for the 'find_patterns' tool. Validates input, delegates to PatternMatcher service, formats and returns the recommendations as MCP CallToolResult.

  private async handleFindPatterns(args: unknown): Promise<CallToolResult> {
    const validatedArgs = InputValidator.validateFindPatternsArgs(args);
    const request = {
      id: crypto.randomUUID(),
      query: validatedArgs.query,
      categories: validatedArgs.categories,
      maxResults: validatedArgs.maxResults,
      programmingLanguage: validatedArgs.programmingLanguage,
    };
  
    const recommendations = await this.patternMatcher.findMatchingPatterns(request);
  
    return {
      content: [
        {
          type: 'text',
          text:
            `Found ${recommendations.length} pattern recommendations:\n\n` +
            recommendations
              .map(
                (rec, index) =>
                  `${index + 1}. **${rec.pattern.name}** (${rec.pattern.category})\n` +
                  `   Confidence: ${(rec.confidence * 100).toFixed(1)}%\n` +
                  `   Rationale: ${rec.justification.primaryReason}\n` +
                  `   Benefits: ${rec.justification.benefits.join(', ')}\n`
              )
              .join('\n'),
        },
      ],
    };
  }

• src/mcp-server.ts:158-186 (registration)

  Registration of the 'find_patterns' tool in the ListToolsRequestSchema handler, including name, description, and input schema definition.

  {
    name: 'find_patterns',
    description:
      'Find design patterns matching a problem description using semantic search',
    inputSchema: {
      type: 'object',
      properties: {
        query: {
          type: 'string',
          description: 'Natural language description of the problem or requirements',
        },
        categories: {
          type: 'array',
          items: { type: 'string' },
          description: 'Optional: Pattern categories to search in',
        },
        maxResults: {
          type: 'number',
          description: 'Maximum number of recommendations to return',
          default: 5,
        },
        programmingLanguage: {
          type: 'string',
          description: 'Target programming language for implementation examples',
        },
      },
      required: ['query'],
    },
  },

• src/utils/input-validation.ts:431-459 (schema)

  Detailed input validation and sanitization for 'find_patterns' tool arguments, enforcing types, lengths, allowed values, and throwing MCP errors on invalid input.

  static validateFindPatternsArgs(args: unknown): {
    query: string;
    categories: string[];
    maxResults: number;
    programmingLanguage?: string;
  } {
    if (typeof args !== 'object' || args === null) {
      throw new McpError(ErrorCode.InvalidParams, 'Invalid arguments: expected object');
    }
    const obj = args as Record<string, unknown>;
    const queryResult = this.validateSearchQuery(obj.query);
    this.throwIfInvalid(queryResult);
  
    const categoriesResult = this.validateCategories(obj.categories);
    this.throwIfInvalid(categoriesResult);
  
    const maxResultsResult = this.validateMaxResults(obj.maxResults);
    this.throwIfInvalid(maxResultsResult);
  
    const langResult = this.validateProgrammingLanguage(obj.programmingLanguage);
    this.throwIfInvalid(langResult);
  
    return {
      query: queryResult.sanitized as string,
      categories: (categoriesResult.sanitized as string[]) ?? [],
      maxResults: (maxResultsResult.sanitized as number) ?? 5,
      programmingLanguage: langResult.sanitized as string | undefined,
    };
  }

• src/services/pattern-matcher.ts:137-166 (helper)

  Core helper implementing the pattern matching algorithm: caching, hybrid semantic/keyword search via performMatching, recommendation building, sorting and limiting results.

  async findMatchingPatterns(request: PatternRequest): Promise<PatternRecommendation[]> {
    try {
      // Check cache first
      const cacheKey = `pattern_match:${request.query}:${JSON.stringify({
        categories: request.categories?.sort(),
        maxResults: request.maxResults,
        programmingLanguage: request.programmingLanguage,
      })}`;
      const cachedResult = this.cache.get(cacheKey);
  
      if (cachedResult) {
        return cachedResult as PatternRecommendation[];
      }
  
      const matches = await this.performMatching(request);
      const recommendations = this.buildRecommendations(matches, request);
  
      // Sort by confidence and limit results
      recommendations.sort((a, b) => b.confidence - a.confidence);
      const finalResults = recommendations.slice(0, request.maxResults ?? this.config.maxResults);
  
      // Cache the results for 30 minutes
      this.cache.set(cacheKey, finalResults, 1800000);
  
      return finalResults;
    } catch (error) {
      structuredLogger.error('pattern-matcher', 'Pattern matching failed', error as Error);
      throw error;
    }
  }