Second Brain

Second Brain is a TypeScript monorepo for saving, organizing, and sharing personal knowledge. The project combines:

• a React + Vite web app for browsing and managing saved content
• an Express + MongoDB API for authentication, brains, items, and sharing
• a Chrome extension for one-click page capture into a selected brain

What the app does

Users can:

• sign up and log in with email/password or Google OAuth
• create multiple personal knowledge collections called brains
• save links, articles, videos, and notes into a selected brain
• search, filter, tag, and inspect saved content
• share a brain publicly through a generated token-based URL
• use the browser extension to save the active page in one click

Project structure

second-brain/
+-- package.json              # root npm workspace scripts
+-- packages/
¦   +-- client/               # React + Vite frontend
¦   +-- server/               # Express + TypeScript API
¦   +-- extension/            # Manifest V3 Chrome extension
+-- README.md

Tech stack

Frontend

• React 18
• Vite
• TypeScript
• Tailwind CSS
• React Router
• Axios
• Lucide React icons

Backend

• Node.js
• Express
• TypeScript
• MongoDB with Mongoose
• JWT authentication
• bcryptjs for password hashing
• Google OAuth integration
• URL metadata extraction with Cheerio
• content safety and source health checks

Browser extension

• Chrome/Chromium Manifest V3
• popup-based login and one-click save action
• stores API URL and auth token in browser storage

Core features

• user registration and login
• Google sign-in flow
• default brain creation for new users
• create, list, search, filter, and delete saved items
• public brain sharing with unique share URLs
• read-only shared brain view for public links
• automatic metadata extraction from URLs
• source availability checks for saved links
• browser extension to save the current tab into a default brain

Environment setup

Server

Create a .env file in packages/server with variables similar to:

MONGODB_URI=mongodb://localhost:27017/second-brain
JWT_SECRET=your-super-secret-jwt-key
GOOGLE_CLIENT_ID=your-google-client-id
GROQ_API_KEY=your-groq-key

The server uses:

• MONGODB_URI for MongoDB connection
• JWT_SECRET for authentication tokens
• GOOGLE_CLIENT_ID for Google login
• GROQ_API_KEY for optional moderation checks

Client

Create a .env file in packages/client if needed:

VITE_API_BASE_URL=http://localhost:5000/api
VITE_GOOGLE_CLIENT_ID=your-google-client-id

Getting started

From the repo root, install dependencies:

npm install

Run the full development stack:

npm run dev

This starts both:

• the server workspace for the API
• the client workspace for the frontend

Useful root scripts

npm run dev:server
npm run dev:client
npm run build
npm run start

Running the app separately

Server

cd packages/server
npm run dev

The API runs by default on port 5000 and exposes endpoints under /api.

Client

cd packages/client
npm run dev

The Vite app serves the main dashboard and authentication UI.

Chrome extension setup

The extension lives in packages/extension.

To load it in Chrome:

1. open chrome://extensions
2. enable Developer mode
3. click Load unpacked
4. select the packages/extension folder

The extension stores the API base URL and auth token in browser storage and can save the active tab into the selected default brain.

Notes

• the backend defaults to mongodb://localhost:27017/second-brain if MONGODB_URI is not set
• a new user is automatically given a default brain during registration or Google login
• a brain becomes public only after the owner clicks the Share action in the dashboard
• the content moderation and source-health checks are part of the item save workflow