5 Mistakes I Made Building My First SaaS (And How to Avoid Them)

After building multiple SaaS products, here are the mistakes I keep seeing (and made myself). 1. Building auth from scratch Every new project: "This time I will build auth properly." Three days later you are debugging OAuth refresh tokens at midnight. Fix: Use Auth.js v5 with a pre-built config. The entire auth layer (email + Google + GitHub, JWT sessions, roles) is 60 lines of code. I wrote a complete guide here . 2. Treating Stripe webhooks as optional You build checkout. It works in test mode. You ship. Then a customer upgrades, downgrades, and you have no idea because you skipped the webhook handler. Fix: Handle these three events from day one: checkout.session.completed — new subscriber invoice.payment_succeeded — renewal customer.subscription.deleted — cancellation Full implementation: Stripe subscriptions guide 3. No AI features In 2026, 70% of new SaaS products have an AI component. If you add it later, you are bolting it onto architecture that was not designed for it. Fix: Sta