Design Patterns MCP Server

Instructions

Implementation Reference

• src/mcp-server.ts:385-489 (handler)

  The main execution logic for the get_pattern_details tool. Validates input, queries the database for pattern details and related implementations, handles cases where the pattern is not found by suggesting similar patterns via semantic search, parses JSON examples, and constructs a formatted markdown response with all details.
  private async handleGetPatternDetails(args: unknown): Promise<CallToolResult> { const validatedArgs = InputValidator.validateGetPatternDetailsArgs(args); const pattern = this.db.queryOne( ` SELECT id, name, category, description, when_to_use, benefits, drawbacks, use_cases, complexity, tags, examples, created_at FROM patterns WHERE id = ? `, [validatedArgs.patternId] ); if (!pattern) { // Try to find similar patterns using semantic search const similarPatterns = await this.semanticSearch.search({ text: validatedArgs.patternId, options: { limit: 3, includeMetadata: true, }, }); if (similarPatterns.length > 0) { return { content: [ { type: 'text', text: `Pattern "${validatedArgs.patternId}" not found. Here are similar patterns:\n\n${similarPatterns .map( (p, i) => `${i + 1}. **${p.pattern.name}** (${p.pattern.category})\n ${p.pattern.description}\n Score: ${(p.score * 100).toFixed(1)}%` ) .join('\n\n')}`, }, ], }; } else { return { content: [ { type: 'text', text: `Pattern "${validatedArgs.patternId}" not found and no similar patterns were found.`, }, ], }; } } const implementations = this.db.query( ` SELECT language, code, explanation FROM pattern_implementations WHERE pattern_id = ? LIMIT 3 `, [validatedArgs.patternId] ); // Parse code examples if available let examplesText = ''; if (pattern.examples) { try { const examples = JSON.parse(pattern.examples); const exampleKeys = Object.keys(examples); if (exampleKeys.length > 0) { examplesText = '\n\n**Code Examples:**\n'; exampleKeys.forEach(lang => { const example = examples[lang]; examplesText += `\n### ${lang.charAt(0).toUpperCase() + lang.slice(1)}\n`; if (example.description) { examplesText += `${example.description}\n\n`; } examplesText += `\`\`\`${lang}\n${example.code}\n\`\`\`\n`; }); } } catch (e) { // If parsing fails, skip examples } } return { content: [ { type: 'text', text: `# ${pattern.name} (${pattern.category})\n\n` + `**Description:** ${pattern.description}\n\n` + `**When to Use:** ${parseArrayProperty(pattern.when_to_use).join(', ')}\n\n` + `**Benefits:** ${parseArrayProperty(pattern.benefits).join(', ')}\n\n` + `**Drawbacks:** ${parseArrayProperty(pattern.drawbacks).join(', ')}\n\n` + `**Use Cases:** ${parseArrayProperty(pattern.use_cases).join(', ')}\n\n` + `**Complexity:** ${pattern.complexity}\n\n` + `**Tags:** ${parseTags(pattern.tags).join(', ')}\n` + examplesText + (implementations.length > 0 ? `\n\n**Implementations:**\n` + implementations .map( impl => `\n### ${impl.language}\n\`\`\`${impl.language.toLowerCase()}\n${impl.code}\n\`\`\`\n${impl.explanation}` ) .join('\n') : ''), }, ], }; }
• src/mcp-server.ts:210-223 (registration)

  Tool registration in the ListToolsRequest handler, defining the tool name, description, and input schema (requiring a patternId string).
  { name: 'get_pattern_details', description: 'Get detailed information about a specific pattern', inputSchema: { type: 'object', properties: { patternId: { type: 'string', description: 'Pattern ID to get details for', }, }, required: ['patternId'], }, },
• src/utils/input-validation.ts:492-505 (schema)

  Input validation schema enforcement for get_pattern_details tool arguments, using patternId validator to ensure valid string format and throw MCP errors on invalid input.
  static validateGetPatternDetailsArgs(args: unknown): { patternId: string; } { if (typeof args !== 'object' || args === null) { throw new McpError(ErrorCode.InvalidParams, 'Invalid arguments: expected object'); } const obj = args as Record<string, unknown>; const patternIdResult = this.validatePatternId(obj.patternId); this.throwIfInvalid(patternIdResult); return { patternId: patternIdResult.sanitized as string, }; }