backend-test-writer
Use when generating tests for backend code (Express routes, MongoDB models, Node services) - analyzes file type, detects test framework from package.json, generates comprehensive tests with setup/teardown and edge case coverage
code-reviewer
Use when asked to review MERN stack code - comprehensive code reviewer that checks project health, security, maintainability, performance, testing, and architecture. Combines general code quality analysis with MERN-specific expertise.
mongodb-query-patterns
Use when writing ANY Mongoose query (.find, .findOne, .findById, .aggregate, .populate), adding database operations to services or controllers, wiring data between services, building endpoints that read or write to MongoDB, or reviewing code that chains service calls. TRIGGER especially when about to write a new findById or pass an ID where a document could be passed instead.