Building a Production SaaS with Next.js 15 and Stripe

Introduction

Building a production-ready SaaS in 2026 has never been more accessible, thanks to Next.js 15 and the Stripe ecosystem. In this article, I'll walk through the key architectural decisions I made when building ReplyMind — my AI-powered social media automation SaaS.

Tech Stack

• Framework: Next.js 15 with App Router
• Language: TypeScript (strict mode)
• Database: PostgreSQL via Supabase
• Payments: Stripe subscriptions + webhooks
• Auth: NextAuth.js v5
• Deployment: Vercel

Setting Up Stripe Subscriptions

The most critical part of any SaaS is billing. Here's how I structured Stripe products:

// Create a checkout session
const session = await stripe.checkout.sessions.create({
  mode: 'subscription',
  payment_method_types: ['card'],
  line_items: [{ price: priceId, quantity: 1 }],
  success_url: `${origin}/dashboard?session_id={CHECKOUT_SESSION_ID}`,
  cancel_url: `${origin}/pricing`,
  customer_email: user.email,
  metadata: { userId: user.id },
})

Webhook Handling

Stripe webhooks are essential for keeping your database in sync with billing events:

// app/api/webhooks/stripe/route.ts
export async function POST(req: Request) {
  const body = await req.text()
  const sig = req.headers.get('stripe-signature')!

  let event: Stripe.Event
  try {
    event = stripe.webhooks.constructEvent(body, sig, process.env.STRIPE_WEBHOOK_SECRET!)
  } catch {
    return new Response('Invalid signature', { status: 400 })
  }

  switch (event.type) {
    case 'customer.subscription.created':
    case 'customer.subscription.updated':
      await syncSubscription(event.data.object as Stripe.Subscription)
      break
    case 'customer.subscription.deleted':
      await cancelSubscription(event.data.object as Stripe.Subscription)
      break
  }

  return new Response(null, { status: 200 })
}

Conclusion

Building a SaaS is a marathon, not a sprint. Focus on shipping early, getting real users, and iterating based on feedback. The tech stack matters less than the problem you're solving.

Check out ReplyMind for a real-world example of everything discussed here.