CreditKit

CreditKit is a starter template for developers building AI applications that need to charge users based on consumption. It handles the billing infrastructure that most pay-per-use products require: credits that get deducted when you call an API, refunds when something fails, and webhook handling that doesn't accidentally double-charge anyone. If you've ever tried to roll your own usage-based billing, you know how many edge cases live in that code. CreditKit packages the hard parts so you can focus on the AI instead of the payment plumbing. It's the kind of unglamorous infrastructure work that's easy to underestimate until you're debugging webhook race conditions at midnight wondering why a customer got charged three times.

The stack is Next.js on the frontend, Supabase for the backend and authentication, and Stripe for payments. That's a common combination for indie developers and small teams shipping fast, and the template fits cleanly into that workflow. You're not adopting a proprietary platform. You get full source code that you own outright, no ongoing licensing fees, no lock-in. It's a one-time purchase and then the code is yours to modify however you want. If you need to customize the billing logic for a specific use case, you can. If you want to rip out Stripe and replace it with something else, you have the source to do that. Ownership matters when you're building something you plan to run for years. You don't want to depend on a billing SaaS that might change its pricing or shut down.

A few implementation details stand out. Credit spend is atomic, meaning transactions either complete fully or roll back, which prevents the partial-deduction bugs that haunt poorly-built billing systems. If the AI call fails halfway through, you don't end up with a user who got charged but didn't get the result. That sounds like an obvious requirement, but it's surprisingly easy to get wrong when you're wiring up a database, a payment processor, and an external API all at once. Stripe webhooks are idempotent, so if the same event fires twice, you don't charge the user twice. This sounds obvious until you've seen the alternative: duplicate charges, customer complaints, manual refunds, support tickets that eat your whole afternoon. Getting idempotency right from the start saves a lot of pain down the road. And there's a background worker that monitors jobs and automatically refunds credits when something fails. These aren't glamorous features, but they're exactly the kind of thing that breaks at scale if you don't get them right from the beginning.

CreditKit is aimed at solo developers and small teams building AI wrappers, chatbots, image generators, transcription services, or any tool where users pay per request rather than per month. The template saves you the weeks you'd otherwise spend wiring up Stripe, handling webhooks defensively, and building a credits ledger that actually stays consistent under load. Most developers underestimate how long this takes because it looks simple on the surface. You think you can knock it out in a weekend. Then you hit the edge cases: what happens when a webhook arrives before the database write completes, what happens when a user triggers multiple jobs in quick succession, what happens when the AI provider times out but eventually returns a result. CreditKit has answers for those questions built in, which means you don't have to discover them the hard way in production.

The price is $129 as a one-time purchase through Gumroad. That's cheap compared to the engineering hours it replaces, especially if you've priced out what it costs to build and test this stuff yourself. A single day of developer time often costs more than the template, and billing code takes more than a day to get right. There's no free tier, but you get the full source immediately and can evaluate whether it fits your needs. If you're serious about shipping a usage-based AI product and don't want to reinvent billing, this is a solid shortcut that gets you to launch faster. The time you save goes directly into the parts of your product that actually differentiate you.

The main limitation is scope. CreditKit solves billing and credits, not authentication, rate limiting, infrastructure deployment, or AI provider integrations. It assumes you're already comfortable with the Next.js and Supabase stack and just need the billing layer handled. If you need a more opinionated full-stack boilerplate that handles everything from auth to deployment, you'll want something broader. But for the narrow problem of credits-based billing with proper webhook handling and automatic refunds, this does the job cleanly. It's a focused solution for a focused problem, and that's usually what you want in a template: something that solves one thing well rather than trying to solve everything mediocrely. Better to compose multiple focused tools than to rely on one bloated boilerplate that does everything poorly.