Balance + Margin Template

Next.js template for AI products that bill cost plus margin against a prepaid balance. Each AI request automatically deducts the real model cost from the AI catalog plus your configured margin.

Two plans (Starter, Pro) with different margins, a multi-model selector, and streaming generation.

Stack: Next.js 16, AI SDK (Gateway), Better Auth, Drizzle ORM, PostgreSQL, Commet SDK

Quick Start#

commet create my-app -t balance-ai
cd my-app
docker compose up -d
pnpm install
pnpm dev

What's Included#

• Two plans with different balances and margins (Starter 50%, Pro 30%)

• Multi-model selector — switch between Claude, GPT, Gemini in one click

• Automatic token tracking via tracked() middleware

• AI model catalog pricing — real cost per model from Commet

• Balance deduction per request (cost + margin)

• Block on exhaustion — requests stop when balance runs out

• AI text generation demo with streaming

• Checkout flow with Commet-hosted payments

• Customer billing portal

How It Works#

User sends prompt → AI Gateway → Response
                        ↓
              tracked() middleware reports:
              - model, inputTokens, outputTokens
                        ↓
              Commet calculates:
              - Real cost (from catalog)
              - Margin (from plan config)
              - Total deducted from balance

Key Files#

• lib/auth/auth.ts — Better Auth + Commet plugin with usage module

• app/api/generate/route.ts — AI endpoint with tracked() middleware

• app/(dashboard)/dashboard/generate-form.tsx — Model selector + streaming

• app/pricing/page.tsx — Dynamic pricing with checkout

• app/checkout/page.tsx — Checkout session creation

• lib/env.ts — Environment validation with t3-env

• lib/commet.ts — SDK initialization

Learn More#

• Consumption Models — Balance model details

• AI Token Billing

• Customer Portal

Run commet create my-app -t balance-ai to start from this template, or browse the source on GitHub.