Why we built AbuseZero: an abuse prevention API for SaaS
Free trial abuse, multi-accounting and credit farming quietly drain SaaS margins. Here's why we built one API that stops repeat benefit claims, with rules you control.
Every SaaS company that gives something away eventually meets the same person many times. They start a free trial, let it run out and start another one with a new email. They collect your signup credits, then collect them again. They turn one free plan into ten. Free trial abuse, multi-accounting and credit farming aren't edge cases. They're the predictable result of giving out a limited benefit to anyone who can create an account.
We built AbuseZero, an abuse prevention API for SaaS, to fix exactly that problem: preventing users from creating extra accounts to repeatedly claim your trials, free plans, credits and other benefits. One API call returns allow or deny, using rules you control.
This post explains why the problem is harder than it looks, why the usual fixes fall short, and what we decided AbuseZero must be.
The problem: one person, many accounts
A benefit is anything you hand out on a limited basis: a 14-day free trial, a $1 introductory month, 500 free AI credits, a free-forever plan with a monthly allowance, a launch promotion. You decide each one should be claimed once, or within a defined limit. The person on the other side decides otherwise.
The cost is real and it compounds. Every repeat claim burns compute, API spend or support time. It also corrupts the numbers you run the business on: trial-to-paid rates look worse than they are, acquisition looks cheaper than it is, and capacity plans are built for users who will never pay. We break the math down in the real cost of free trial abuse.
And it rarely arrives slowly. These are real stories from teams in our early beta, from before they had protection:
- A team woke up to a $6,000 OpenAI bill. Someone had created hundreds of free accounts and used up the complimentary AI credits on every one of them.
- A team whose cloud bill normally ran $200 to $300 a month woke up to a $12,000 bill. Automated registrations had triggered thousands of expensive serverless functions, database operations and background jobs overnight.
- After a launch went viral on X, one team gained 6,400 new users in a month. 2,700 of them were duplicate accounts. About 32 became paying customers.
None of that is growth. All of it is cost.
The companies that feel this most are the ones whose benefits cost the most to deliver: AI applications, API businesses, developer tools and generation platforms, where every free credit is paid for in model or infrastructure spend.
Why the usual fixes fall short
Most teams try the same sequence of fixes. Each one helps a little, and each one has a ceiling.
| Approach | What it checks | Where it stops |
|---|---|---|
| Email verification | That an inbox exists | New inboxes, aliases and disposable addresses take seconds |
| CAPTCHA | That someone is probably human | A real human claiming twice passes every time |
| Phone or card required | That a number or card exists | Adds friction for every real user, and determined abusers adapt |
| Hand-written rules | Whatever you thought of last month | Brittle, untested, and blind to anything new |
| Fraud platforms | Payment and account risk | Built for transactions, not for who should receive a benefit |
The gap is the same in every row. These tools answer is this a real person? or is this payment risky? The question that matters for a free trial is different: has this person already received this benefit? A real, polite, perfectly human person can still be claiming your trial for the fifth time.
Answering that question well means connecting a new claim to everything your product has already given out, across changing emails, devices, networks and payment methods, in real time, without slowing down the people you actually want. That is a large, specialized system. Most SaaS teams shouldn't have to build it, and the ones that try find it never stops needing work. We cover the trade-offs of each approach in how to prevent free trial abuse.
See it on your own traffic
Put a benefit in observe mode and AbuseZero records what it would have decided on every claim, while every user is still allowed. You see your real repeat-claim picture before you block anyone. See pricing or start with Builder.
What we decided AbuseZero must be
We started from a short list of principles, and every part of the product answers to them.
One question, one answer
AbuseZero answers one question: should this claim receive this benefit? Your server sends the claim, and AbuseZero returns allow or deny, an AbuseZero Risk Score from 0 to 100 and a readable reason. No dashboards to watch and no queue of reviews before your user can continue.
Depth on every claim
Behind that one call sits the AbuseZero AI Risk Engine: a proprietary algorithm built on 140,000+ risk signal combinations, with AI that checks the claim again alongside it. Every claim is checked against your workspace's full claim history and assessed across identity, device, network, automation and benefit history, all inside the same request. You get the result of all that work without carrying any of it. Read more about the AbuseZero AI Risk Engine.
Rules you control
You know your product. We don't pretend otherwise. Every benefit starts on an AbuseZero-managed protection level (Lenient, Balanced or Strict), and you add your own custom rules and allow and block lists on top. Change a rule in the dashboard and it applies to the next claim. Your application code doesn't change.
Fair to real users
A shared office network or a family laptop doesn't prove two accounts belong to one person, and AbuseZero isn't built to pretend it does. You can see what AbuseZero would decide before it affects anyone, replay a change against your recent traffic, and let specific users through at any time. We wrote a full guide to multi-accounting detection without false positives.
Simple to integrate
Keep your signup flow. Add one server-side call where the benefit is granted. Use the AbuseZero REST API, the AbuseZero Node.js SDK, the AbuseZero CLI or the AbuseZero MCP server, whichever fits your team. The step-by-step integration guide shows exactly where the call goes.
What AbuseZero is not
Being clear about the edges matters as much as the features. AbuseZero is focused on repeat abuse of limited benefits. It isn't a general fraud platform, an identity verification service or a payment fraud tool, and it doesn't replace your authentication. Your application still manages sign-in, payments, delivery and ongoing usage limits. AbuseZero decides who should receive the benefit, and your application acts on that decision. We map the differences in abuse prevention vs fraud detection vs identity verification.
Detection also depends on the evidence available. No honest system can promise one account per person or catch every abusive claim, and we won't. What we promise is a serious, continuously improving answer to the question your other tools don't ask.
Who AbuseZero is for
AbuseZero is for SaaS companies that offer trials, free plans, introductory credits, promotions or other benefits that can be farmed through multiple accounts, especially when each one has a real cost to deliver:
- AI applications giving free generations, tokens or credits. See how to protect signup credits in an AI app.
- API businesses with free tiers and introductory usage. See how to stop free tier abuse on an API product.
- Developer tools with trials, free seats or free build minutes
- Indie hackers and first-time founders launching a SaaS on X, often built with an AI coding agent. See going viral on X?
- Any SaaS product with a $1 trial, a free-forever plan or a promotion it wants claimed once. See $1 trial abuse.
If an offer isn't meant to be claimed endlessly, AbuseZero helps keep it that way.
Frequently asked questions
What is an abuse prevention API?
An abuse prevention API is a service your server calls when a user requests something you give out on a limited basis. AbuseZero evaluates the claim against your rules and your full claim history, and returns allow or deny so your application can grant or decline the benefit.
How is AbuseZero different from a CAPTCHA or bot detector?
A CAPTCHA checks whether someone is probably human. AbuseZero checks whether this person should receive this benefit, even when they're a real person. It also tells harmful automation apart from the AI agents you choose to trust. See AI agents are claiming your free trials.
Does AbuseZero make the final decision?
No. AbuseZero returns the result, and your application stays in control of account creation, benefit delivery and enforcement.
How much does AbuseZero cost?
Start with Builder and pay as you go, or choose a Pro or Scale plan with monthly credits. Large workspaces can talk to us about Enterprise. Current prices are on the pricing page.
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Keep reading
- The real cost of free trial abuse for SaaS and AI apps
- How to prevent free trial abuse, starting with the offer itself
- Multi-accounting detection without blocking real users
- Add a trial and credit abuse check to your signup flow
- Abuse prevention vs fraud detection vs identity verification
- AI agents are claiming your free trials. Let the right ones in.
- Vibe coded your SaaS? Don't wake up to a $6,000 bill