Adding Features to Your GPT Engineer App

GPT Engineer produces UI-heavy prototypes. The backend, if it exists, is minimal. Most projects need substantial backend development to become functional applications

Complete backend development (database, API, auth). Stripe payments. Email integration. File uploads. Admin dashboards. Real-time features. User account management

Almost every SaaS app needs payment processing. Stripe is the standard — it handles credit cards, subscriptions, invoices, and payouts. The key pieces: a checkout flow for collecting payment, webhooks to update your database when payments succeed or fail, and a customer portal for managing subscriptions. GPT Engineer might generate a basic checkout page, but the webhook handling and subscription lifecycle management usually need to be built by hand.

Your app needs user accounts with secure login. The easiest options: NextAuth (for Next.js), Supabase Auth, or Clerk. These handle email/password login, social login (Google, GitHub), password resets, and session management. Don't build auth from scratch — the security implications are too complex for a first implementation.

Transactional emails — welcome emails, password resets, order confirmations — require an email service provider. Resend is the simplest to set up, SendGrid is the most established, and Amazon SES is the cheapest at scale. You'll need email templates, a sending service, and proper DNS configuration (SPF, DKIM) so your emails don't land in spam.

If a feature requires deep technical expertise (payment compliance, data privacy, real-time systems), it's faster and safer to get professional help than to iterate with AI tools. Our team adds features like these to GPT Engineer apps every week — we know the patterns and the pitfalls.