Everything You Need to Study. Powered by AI.

Create comprehensive notes, visual diagrams, MCQ quizzes, and downloadable PDFs designed for exams.

Live App · React + Express + Gemini · Deployed on Vercel & Railway

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🌟 What it does

NoteSprint AI is an AI study partner for students. Sign in with Google, get 50 free credits, type a topic ("TCP vs UDP", "Photosynthesis", "Newton's Laws") and Gemini generates a complete study document:

• 📚 Exam-focused notes — markdown with headings, definitions, examples and exam tips, at three detail levels (brief / standard / detailed)
• ⭐ Ranked subtopics — frequently asked / very important / important chips
• ⚡ Quick-revision sheet and practice questions (short + long)
• 🧭 Flow diagrams — AI-written Mermaid, rendered as real SVG flowcharts
• 📊 Charts — AI-chosen bar / line / pie data rendered with Recharts
• 🧠 Quiz Mode — 10 AI-generated MCQs grounded in each note, with instant right/wrong feedback, explanations and a final score; retakes are free (quiz is cached per note)
• 📄 One-click PDF download with the exact page layout (works on mobile)
• 💳 Credit system with Stripe — 10 credits per note, 5 credits per quiz, buy more on the pricing page
• ✉️ Welcome email on first sign-up — queued through Redis + BullMQ
• 🗂 History — every note saved, browsable, re-downloadable, deletable

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🏗️ Architecture

Request flow: The React SPA (Vercel) authenticates via Firebase's Google popup, then talks to the Express API (Docker container on Railway) with an httpOnly JWT cookie. The API builds a strict JSON prompt, calls Gemini through LangChain, stores the result in MongoDB Atlas and deducts credits. Stripe Checkout handles payments — credits are only granted by the webhook, never the redirect. First-time sign-ups enqueue a welcome-email job in Redis (BullMQ); an in-process worker sends it via SMTP with a graceful direct-send fallback if Redis is down.

🛠️ Tech Stack

Layer	Tech
Frontend	React 19, Vite, Tailwind CSS 4, Redux Toolkit, Framer Motion, react-markdown, Mermaid, Recharts
Auth	Firebase Google sign-in (client) → JWT in httpOnly cookie (server)
Backend	Node.js, Express 5, Mongoose, LangChain (@langchain/google-genai), BullMQ, Nodemailer + Mailgen
Data & Infra	MongoDB Atlas, Redis (Docker locally / Key Value in prod), Docker, Vercel, Railway
Payments	Stripe Checkout + signed webhooks

⚡ Engineering Problems Solved

Problem	Root cause	Fix
Logout worked locally, silently failed in production	Cross-site cookie deletion: clearCookie without SameSite=None; Secure is rejected by browsers on cross-origin responses	Shared cookieOptions object used by both res.cookie and res.clearCookie
Gemini randomly returned "invalid JSON"	Output-token truncation — diagnosed via the finishReason field	Explicit maxOutputTokens, JSON response mode, retry on parse failure
PDF download printed the whole page on mobile	Mobile browsers don't support the iframe-print technique used by react-to-print	Plain window.print() + print:hidden CSS on everything except the note
Stripe webhook always failed signature verification	Global express.json() consumed the raw body the signature is computed over	Webhook route mounted with express.raw() before the JSON parser
White screen after adding new libraries	A stray root node_modules introduced a second copy of React; Vite's dep cache kept serving it	Removed duplicate install, cleared node_modules/.vite
Mermaid spammed "Syntax error" into the page	Mermaid v11 injects error SVGs into document.body on parse failures	suppressErrorRendering: true + sanitizing AI-generated labels
Sandbox testers could buy unlimited credits	Test-mode payments are free	Server-side credit cap (500) enforced before creating a checkout session
Concurrent generations sometimes failed	Free-tier Gemini throttles parallel requests per key	Retries with backoff now; billing tier / BullMQ job queue as the scale path

🚀 Run It Locally

Prereqs: Node 20+, Docker Desktop, a MongoDB Atlas cluster, a Gemini API key, a Firebase project (Google sign-in enabled), Stripe test keys, and SMTP credentials (e.g. Gmail app password).

git clone https://github.com/musama-dev/NoteSprint.git

# 1. backend
cd backend
npm install
docker compose up -d        # starts Redis on :6379
# create backend/.env (see table below)
npm run dev                 # http://localhost:5000

# 2. frontend (new terminal)
cd frontend
npm install
# create frontend/.env with VITE_FIREBASE_APIKEY=<your firebase web api key>
npm run dev                 # http://localhost:5173

# 3. stripe webhooks (optional, new terminal)
stripe listen --forward-to localhost:5000/api/payment/webhook

backend/.env

Variable	Purpose
PORT	API port (5000 in dev; Railway / Render injects its own)
MONGO_URI	MongoDB Atlas connection string
JWT_SECRET	Signs the auth cookie
NODE_ENV	development / production (controls cookie flags)
FRONTEND_URL / CLIENT_URL	Frontend origin — CORS + Stripe redirects + email links
GEMINI_API_KEY	Google AI Studio key
GEMINI_MODEL	Optional model override (default gemini-3.6-flash)
STRIPE_SECRET_KEY / STRIPE_WEBHOOK_SECRET	Stripe test keys
SMTP_HOST / SMTP_PORT / SMTP_USER / SMTP_PASS / SENDER_EMAIL	Welcome-email SMTP
REDIS_URL	Optional locally (defaults to redis://localhost:6379); Redis Key Value URL in prod

📡 API Overview

Method & path	Auth	Purpose
POST /api/auth/google	—	Sign in / first-time sign-up (queues welcome email)
POST /api/auth/logout	—	Clear session cookie
GET /api/user/me	🔒	Current user + credits
POST /api/notes/generate	🔒	Generate notes (10 credits)
GET /api/notes/my-notes	🔒	All of the user's notes, newest first
DELETE /api/notes/:id	🔒	Delete own note
POST /api/notes/:id/quiz	🔒	Generate a 10-question MCQ quiz for a note (5 credits, cached — retakes free)
POST /api/payment/checkout	🔒	Create Stripe Checkout session (credit cap enforced)
POST /api/payment/webhook	Stripe signature	Grant credits on checkout.session.completed
GET /api/health	—	Uptime / wake-up check

🌐 Deployment Notes

• Frontend → Vercel. Add the production domain (notesprint-ai.vercel.app) to Firebase's authorized domains.
• Backend → Railway (Docker runtime, root directory .). Set all env vars (PORT=5000, MONGO_URI, GEMINI_API_KEY, etc.).
• MongoDB Atlas: Allow 0.0.0.0/0 in Network Access so Railway container can connect.
• Stripe: Add a webhook endpoint for checkout.session.completed pointing at /api/payment/webhook.

🗺️ Roadmap

• Quiz Mode — MCQ practice tests generated from notes
• Flashcards generated from notes (with Anki export)
• Verify Firebase ID tokens server-side (firebase-admin) instead of trusting the client
• Move note generation itself onto the BullMQ queue with real progress
• Per-user rate limiting
• Paid Gemini tier for true concurrent generation
• Custom domain

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Built by Muhammad Usama — React · Express · MongoDB · Gemini AI