Backend Development: Design, implement, and maintain RESTful and GraphQL APIs using Node.js and Express. Model, query, and optimize data across relational and NoSQL databases (MySQL, PostgreSQL, MongoDB, Redis). Ensure data integrity, performance, and scalability across services. Build and maintain services and data flows that support the product's scoring and personalization features. Integration and Collaboration: Work with front end engineers to define clear API contracts and ensure smooth data flow into applications. Collaborate with the data team on pipelines, storage, and query performance. Participate in code reviews, technical design discussions, and architectural decisions. Quality and Maintenance: Write unit and integration tests to keep services stable. Keep code clean, well-documented, and reusable. Debug, optimize, and monitor service performance, reliability, and security.