RAGmonsters Custom PostgreSQL MCP Server

Instructions

Implementation Reference

• src/mcp-server/tools/monsters.js:34-123 (handler)

  The core handler function for the getMonsters tool. It constructs a dynamic SQL query based on input parameters (filters, sort, limit, offset), executes it using the database pool, and returns a formatted list of monsters.
  export async function getMonsters(params = {}) { try { if (!dbPool) { throw new Error('Database pool not initialized. Call initialize() first.'); } logger.info(`getMonsters called with params: ${JSON.stringify(params)}`); const { filters = {}, sort = {}, limit = 10, offset = 0 } = params; // Start building the query let query = ` SELECT m.monster_id, m.name, m.category, m.habitat, m.rarity, m.primary_power, m.secondary_power, m.special_ability FROM monsters m WHERE 1=1 `; // Build parameter array for prepared statement const queryParams = []; // Add filters if (filters.category) { queryParams.push(filters.category); query += ` AND m.category = $${queryParams.length}`; } if (filters.habitat) { queryParams.push(filters.habitat); query += ` AND m.habitat = $${queryParams.length}`; } if (filters.rarity) { queryParams.push(filters.rarity); query += ` AND m.rarity = $${queryParams.length}`; } // Add sorting if (sort.field) { // Validate sort field to prevent SQL injection const validSortFields = ['name', 'category', 'habitat', 'rarity']; const sortField = validSortFields.includes(sort.field) ? sort.field : 'name'; // Validate sort direction const sortDirection = sort.direction?.toLowerCase() === 'desc' ? 'DESC' : 'ASC'; query += ` ORDER BY m.${sortField} ${sortDirection}`; } else { // Default sort by name query += ` ORDER BY m.name ASC`; } // Add pagination query += ` LIMIT $${queryParams.length + 1} OFFSET $${queryParams.length + 2}`; queryParams.push(limit, offset); const monsters = await executeQuery(dbPool, query, queryParams); logger.info(`getMonsters returning ${monsters.length} monsters`); logger.debug(`First monster in results: ${JSON.stringify(monsters[0] || {})}`); // Format the response return { content:monsters.map(monster => ({ type: 'text', text: JSON.stringify({ id: monster.monster_id, name: monster.name, category: monster.category, habitat: monster.habitat, rarity: monster.rarity, powers: { primary: monster.primary_power, secondary: monster.secondary_power, special: monster.special_ability } }), }))}; } catch (error) { logger.error(`Error in getMonsters: ${error.message}`); logger.error(error.stack); throw error; } }
• src/mcp-server/tools/index.js:17-36 (registration)

  Registers the getMonsters tool with the MCP server instance, linking the handler function and defining the input schema.
  server.addTool({ name: 'getMonsters', description: 'Get a list of monsters with optional filtering, sorting, and pagination', parameters: z.object({ filters: z.object({ category: z.string().optional().describe('Filter by monster category'), habitat: z.string().optional().describe('Filter by monster habitat'), rarity: z.string().optional().describe('Filter by monster rarity') }).optional().describe('Optional filters for the query'), sort: z.object({ field: z.string().optional().describe('Field to sort by (name, category, habitat, rarity)'), direction: z.enum(['asc', 'desc']).optional().describe('Sort direction (asc or desc)') }).optional().describe('Optional sorting parameters'), limit: z.number().optional().describe('Maximum number of results to return (default: 10)'), offset: z.number().optional().describe('Number of results to skip for pagination (default: 0)') }), execute: getMonsters });
• src/mcp-server/tools/index.js:20-34 (schema)

  Zod schema defining the input parameters for the getMonsters tool: filters (category, habitat, rarity), sort (field, direction), limit, offset.
  parameters: z.object({ filters: z.object({ category: z.string().optional().describe('Filter by monster category'), habitat: z.string().optional().describe('Filter by monster habitat'), rarity: z.string().optional().describe('Filter by monster rarity') }).optional().describe('Optional filters for the query'), sort: z.object({ field: z.string().optional().describe('Field to sort by (name, category, habitat, rarity)'), direction: z.enum(['asc', 'desc']).optional().describe('Sort direction (asc or desc)') }).optional().describe('Optional sorting parameters'), limit: z.number().optional().describe('Maximum number of results to return (default: 10)'), offset: z.number().optional().describe('Number of results to skip for pagination (default: 0)') }),
• src/mcp-server/tools/monsters.js:14-17 (helper)

  Initialization function for the monsters tools module, setting up the shared database connection pool required by the handlers.
  export function initializeTools(pool) { dbPool = pool; logger.info('Monsters module initialized with database pool'); }