Building a Viral Waitlist With Next.js, Prisma, and Resend (With Referral Tracking)

A waitlist is often the first real infrastructure a SaaS needs. Done right, it validates demand, builds an email list, and creates social proof. Here's the full stack implementation.

What We're Building

• Waitlist signup form with email + optional name
• Confirmation email sent immediately (Resend)
• Position tracking (show users their spot)
• Referral tracking for viral growth
• Admin endpoint to batch-invite users

Database Schema

model WaitlistEntry {
  id          String   @id @default(cuid())
  email       String   @unique
  name        String?
  position    Int      @unique @default(autoincrement())
  referralCode String  @unique @default(cuid())
  referredBy  String?  // referralCode of the person who referred them
  referralCount Int    @default(0)
  status      String   @default("waiting") // waiting | invited | active
  invitedAt   DateTime?
  createdAt   DateTime @default(now())

  @@index([status])
  @@index([referralCode])
}

Signup API Route

// app/api/waitlist/route.ts
import { NextRequest } from 'next/server'
import { z } from 'zod'
import { db } from '@/lib/db'
import { Resend } from 'resend'

const resend = new Resend(process.env.RESEND_API_KEY)

const SignupSchema = z.object({
  email: z.string().email(),
  name: z.string().max(100).optional(),
  referralCode: z.string().optional()
})

export async function POST(request: NextRequest) {
  const body = await request.json()
  const parsed = SignupSchema.safeParse(body)
  if (!parsed.success) {
    return Response.json({ error: 'Invalid input' }, { status: 400 })
  }

  const { email, name, referralCode } = parsed.data

  // Check if already signed up
  const existing = await db.waitlistEntry.findUnique({ where: { email } })
  if (existing) {
    return Response.json({ position: existing.position, referralCode: existing.referralCode })
  }

  // Find referrer
  let referredBy: string | undefined
  if (referralCode) {
    const referrer = await db.waitlistEntry.findUnique({ where: { referralCode } })
    if (referrer) {
      referredBy = referralCode
      await db.waitlistEntry.update({
        where: { id: referrer.id },
        data: { referralCount: { increment: 1 } }
      })
    }
  }

  const entry = await db.waitlistEntry.create({
    data: { email, name, referredBy }
  })

  // Send confirmation email
  await resend.emails.send({
    from: 'Atlas <[e-mail]>',
    to: email,
    subject: "You're on the waitlist!",
    html: `
      <h2>You're #${entry.position} on the waitlist!</h2>
      <p>Move up by referring friends:</p>
      <p><strong>Your referral link:</strong></p>
      <p>${process.env.NEXT_PUBLIC_SITE_URL}/waitlist?ref=${entry.referralCode}</p>
      <p>Each friend who signs up bumps you up the list.</p>
    `
  })

  return Response.json({ position: entry.position, referralCode: entry.referralCode }, { status: 201 })
}

Signup Form

// components/waitlist-form.tsx
'use client'
import { useState } from 'react'
import { useSearchParams } from 'next/navigation'

export function WaitlistForm() {
  const searchParams = useSearchParams()
  const referralCode = searchParams.get('ref') ?? ''
  const [state, setState] = useState<'idle' | 'loading' | 'success' | 'error'>('idle')
  const [result, setResult] = useState<{ position: number; referralCode: string } | null>(null)

  async function handleSubmit(e: React.FormEvent<HTMLFormElement>) {
    e.preventDefault()
    setState('loading')
    const form = new FormData(e.currentTarget)

    const res = await fetch('/api/waitlist', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        email: form.get('email'),
        name: form.get('name'),
        referralCode
      })
    })

    if (res.ok) {
      const data = await res.json()
      setResult(data)
      setState('success')
    } else {
      setState('error')
    }
  }

  if (state === 'success' && result) {
    return (
      <div className='text-center'>
        <h3 className='text-xl font-semibold'>You're #{result.position}!</h3>
        <p className='mt-2 text-muted-foreground'>Share your link to move up:</p>
        <code className='block mt-2 p-2 bg-muted rounded text-sm'>
          {window.location.origin}/waitlist?ref={result.referralCode}
        </code>
      </div>
    )
  }

  return (
    <form onSubmit={handleSubmit} className='flex flex-col gap-3 max-w-sm mx-auto'>
      <input name='name' type='text' placeholder='Your name (optional)' className='input' />
      <input name='email' type='email' placeholder='[e-mail]' required className='input' />
      <button type='submit' disabled={state === 'loading'} className='btn-primary'>
        {state === 'loading' ? 'Joining...' : 'Join Waitlist'}
      </button>
      {state === 'error' && <p className='text-red-500 text-sm'>Something went wrong. Try again.</p>}
    </form>
  )
}

Admin: Batch Invite

// app/api/admin/waitlist/invite/route.ts
export async function POST(request: Request) {
  // Verify admin auth
  const adminKey = request.headers.get('x-admin-key')
  if (adminKey !== process.env.ADMIN_SECRET_KEY) {
    return Response.json({ error: 'Unauthorized' }, { status: 401 })
  }

  const { count = 10 } = await request.json()

  // Get next batch of waiting users
  const toInvite = await db.waitlistEntry.findMany({
    where: { status: 'waiting' },
    orderBy: [{ referralCount: 'desc' }, { position: 'asc' }], // Referrers first
    take: count
  })

  // Send invites
  await Promise.all(toInvite.map(async (entry) => {
    await resend.emails.send({
      from: 'Atlas <[e-mail]>',
      to: entry.email,
      subject: "Your invite is here!",
      html: `<h2>You're in!</h2><p><a href='${SITE_URL}/signup?email=${entry.email}'>Create your account</a></p>`
    })

    await db.waitlistEntry.update({
      where: { id: entry.id },
      data: { status: 'invited', invitedAt: new Date() }
    })
  }))

  return Response.json({ invited: toInvite.length })
}

Pre-Built in the Starter

The AI SaaS Starter includes the full waitlist system:

• Signup form with position display
• Referral tracking
• Confirmation emails via Resend
• Admin invite endpoint
• Analytics on signup rate and referral performance

AI SaaS Starter Kit -- $99 one-time -- waitlist system included. Clone and ship.

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Comments

[Mihir kanzariya]

Nice setup. A couple of production things worth watching for if you ship this to real users:

The referralCount increment has a race condition. If two people sign up with the same referral code at the same time, both findUnique calls return the same count, and one increment gets lost. Using Prisma's { increment: 1 } atomic update (which you're already doing) handles this at the database level, so you're actually fine there. But the findUnique + update is still two queries without a transaction. If the create fails after the referrer count was already incremented, you end up with a phantom referral. Wrapping the referrer update and the new entry creation in a $transaction block fixes that.

Referral fraud is the bigger concern at scale. Someone can create throwaway email addresses and sign up 50 times with their own referral code to jump the queue. Common mitigations: rate-limit signups per IP (not bulletproof but raises the effort), require email verification before the referral counts, and cap the max referrals that actually affect queue position (e.g. referrals beyond 10 don't move you up further).

One more edge case: the position field uses @default(autoincrement()) which gives you insertion order, but if you want referrals to "bump you up the list," you'd need to actually reorder positions or use a separate priority score. Right now the position is static after signup. A simpler approach is to sort by referralCount DESC, position ASC at read time instead of trying to rewrite positions.