Study Buddy is a learning platform for school students, built around a Socratic AI tutor that guides students toward answers instead of handing them over. I built the complete backend (a versioned NestJS REST API with 19 documented endpoint groups, Swagger docs and a unified response envelope) and the Next.js admin dashboard. Students pick a grade level, browse subjects and topics, chat with the tutor, take server-graded adaptive quizzes and build daily study streaks. Because many users are minors, sign-up detects age from date of birth and triggers a five-clause parental consent flow by email before access is unlocked. Free and Pro tiers are enforced server-side (daily AI question quotas, Pro-only custom subjects and notes) with Stripe Checkout, webhooks and a sandbox fallback. Admins manage the curriculum hierarchy, quizzes, users, consent compliance, subscriptions and revenue, and tune the AI at runtime (model, temperature, safety level, system prompts) with per-request token and cost logs. The mobile app (iOS & Android) was built by a teammate on top of this API.