My name is John Moore. I run JMS Dev Lab from Cork, Ireland. Before I was a developer, I spent 22 years running jewellery retail stores. I managed stock, staff, suppliers, and — most importantly — margins.
That retail background is why ProfitShield exists. I built it because I lived the problem it solves.
In retail, you learn quickly that revenue is vanity. What matters is what you keep after costs. A shop doing half a million in sales sounds impressive until you realise the margins are so thin that the owner is taking home less than an employee.
When I moved into building software for Shopify merchants, I saw the same pattern playing out online — but worse. At least in a physical shop, you have a rough sense of your costs. You know what you paid for the stock, what the rent is, what the staff cost. The margins aren't perfect, but you have a feel for them.
Online, the costs are more fragmented and harder to see. Payment processing fees are buried in your Shopify Payments statement. Shipping costs vary by order. Discount codes stack in ways you didn't intend. Returns eat into margins that looked healthy on the day the order shipped.
I kept meeting Shopify merchants who were celebrating revenue growth while their actual profit was flat or declining. They were selling more but keeping less. Some of them were genuinely losing money on a significant percentage of their orders without knowing it.
There are plenty of Shopify profit tracking apps. Most of them do a good job of one thing: telling you what happened. They import your costs, match them against your orders, and give you reports showing your margins over time.
That is useful information. But it comes after the sale. By the time you see a report showing that 12% of last month's orders were unprofitable, those orders have already shipped. You have already paid the shipping. You have already absorbed the payment processing fee. The money is gone.
What I wanted was something that works the other way around. Instead of reporting on bad orders after they happen, what if you could prevent them from happening in the first place?
That is the core idea behind ProfitShield. It calculates the true profitability of an order at checkout — factoring in COGS, payment processing, shipping, and discounts — and if the order falls below your configured margin threshold, it blocks it before it goes through.
Blocking an order at checkout is a sensitive operation. You cannot afford latency. If the checkout slows down or feels broken, customers abandon their carts and you lose the good orders along with the bad ones.
This is why we built ProfitShield on Shopify Functions, which run in Rust at the edge. For non-technical readers, that means the code runs on servers physically close to your customers, in a programming language designed for speed. The margin calculation happens in milliseconds. Your customers never notice it.
We considered building this as a standard Shopify app that intercepts orders through webhooks, but that approach introduces delay and reliability issues. If your server is slow or down, orders either slip through unchecked or the checkout breaks entirely. Neither is acceptable.
Shopify Functions are the right tool for this job. They run inside Shopify's own infrastructure, so they are as fast and reliable as Shopify itself. The trade-off is that they are harder to build — you are writing Rust, not JavaScript — but for the merchant, the result is a checkout that works exactly as expected, just smarter about which orders it allows.
At its core, ProfitShield does three things:
ProfitShield is new. I am not going to pretend we have thousands of merchants or years of case studies. We don't. We are at the beginning.
What I can say is that the problem is real. I have seen it in my own retail businesses over two decades, and I have seen it again in the Shopify merchants I have worked with since starting JMS Dev Lab. Merchants are losing money on orders they think are profitable, and by the time they figure it out from their accounting, the damage is already done.
The technical approach is sound. Shopify Functions are the right way to intervene at checkout without degrading the customer experience. Rust gives us the performance guarantees we need. And the margin calculations are straightforward accounting — not a black box.
If you are a Shopify merchant and you have ever looked at your bank balance and wondered why it doesn't match your sales dashboard, ProfitShield might help you understand the gap.
ProfitShield has a 14-day free trial on all plans. Starter is $19/month, Pro is $49/month, and Business is $149/month depending on the features you need.
Even if you just run it for the trial period, you will learn something useful about your per-order economics. Sometimes the most valuable thing a tool can do is show you a number you have been ignoring.
Visit profitshield.app to get started, or get in touch if you have questions. I am happy to talk margins with anyone — it is one of the few topics where 22 years of retail actually comes in handy.