Built a Chrome extension for LeetCode that adds a “Remind Me” button to problem pages, enabling spaced repetition with automated email reminders after 3, 6, 12, and 24 days. Developed a full-stack system with a Node.js/Express backend (deployed on Railway) using PostgreSQL, Gmail SMTP (via Nodemailer) for email delivery, and cron-based scheduling. Implemented features like progress tracking, secure API with rate limiting, and a responsive UI seamlessly integrated into LeetCode's interface.