Balance + Margin Template

Balance-based billing template for AI products. Customers prepay a balance, and each AI request automatically deducts the real cost (from the AI model catalog) plus your configured margin. Two plans (Starter, Pro) with different margins.

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