NexPay

NexPay is an AI-powered crypto payment app that lets you send and swap tokens just by chatting in plain English. Instead of dealing with complex wallet interfaces, you simply type something like "Send 10 USDC to John" or "Swap 0.5 ETH to USDC" and the AI understands your intent, builds the transaction, and asks for your confirmation before executing it.

The backend is built with Fastify and TypeScript, uses Groq's Llama AI model to process user messages, Prisma with PostgreSQL for storing chat history and transactions, and Uniswap V3 for swap quotes on Sepolia testnet. Users authenticate with their wallet address and can save contacts for easy transfers.

The idea came from a real problem — existing crypto users waste time repeating the same manual steps every time they do a transaction, and new Web3 users get completely lost trying to figure out where to click and what to do. NexPay solves both problems with one solution: a conversational AI agent that acts as a personal Web3 assistant.

For the frontend I used React, with MetaMask and Privy for wallet authentication — covering both experienced users who already have MetaMask and complete beginners who can sign up with just an email via Privy.

The backend is built with Fastify and TypeScript in a Turborepo monorepo. I used Groq's Llama 3.3 70B model to process natural language messages like "Send 20 USDC to Abhinav" — the AI understands the intent, extracts the details, validates the contact from the user's saved list, builds the transaction, and returns it ready for confirmation. No manual steps needed.

For swaps I integrated Uniswap V3 directly — when a user says "Swap 0.5 ETH to USDC", the backend fetches a live quote from the Uniswap Quoter contract on Sepolia, builds the exact calldata, and sends it to the frontend for signing. Prisma with PostgreSQL on Neon handles all chat history, contacts and transaction records.