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: Start with AI-ready infrastructure. A streaming chat endpoint is ~40 lines. Conversation persistence is one Prisma model. Plan-based usage limits are a simple count query.
4. Reinventing the landing page
You spend a week on your marketing page. It looks decent but converts poorly because you did not follow the patterns that actually work.
Fix: Use the proven structure: badge → headline → subheadline → dual CTA → code preview → features → pricing → final CTA. I covered this in SaaS landing page guide.
5. Not using TypeScript strict mode
You start with regular TypeScript. Six months later your codebase has any everywhere and runtime errors that should have been caught at compile time.
Fix: Start strict. It is harder for the first week and saves you months of debugging later.
The shortcut
I got tired of making these mistakes, so I built LaunchKit — a starter kit that avoids all five from day one. Auth, billing, AI, email, TypeScript strict, beautiful UI. All pre-wired.
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