A practical guide to Shopify POS integration: what the Admin API covers, use cases, product and inventory sync, webhooks, and how to build it right.
Shopify is best known as the platform behind millions of online stores, but its retail arm, Shopify POS, brings that same catalog and order system into a physical shop. The appeal is a single source of truth. The products you sell online and the products you ring up at the counter come from the same place, and a sale in either channel updates the same inventory. For a business that sells both online and in person, that unified picture is the whole point.
A Shopify POS integration is the software connection that ties Shopify into the rest of your operation, or that extends what the register can do at checkout. Sometimes that means pushing order and inventory data into an accounting system or a warehouse tool. Sometimes it means building a checkout extension so staff see custom information or run a custom action while ringing up a sale. Either way, you are working with Shopify's developer platform, which has its own structure and its own rules.
This guide explains what a Shopify integration involves, the API concepts that matter, and the decisions you will face when you connect Shopify to something custom. We build these connections for Toronto retailers and merchants, and the aim here is to be genuinely useful whether or not you hire us. A scoping conversation is always free and never carries an obligation.
The main way software talks to Shopify is the Admin API, the interface that lets an approved app read and write a store's data, including products, variants, inventory, orders, customers, and more. Shopify offers this through a GraphQL API, where you ask for exactly the fields you want in a single request, which is efficient and precise. Understanding that you request specific data rather than pulling everything is the first mental shift for anyone new to the platform.
For the register itself, Shopify provides POS extensions, a way to add custom features to the point of sale app. An extension can show extra information on the cart screen, add a custom action a cashier can tap, or apply logic during checkout. If your project is about changing what happens at the counter rather than moving data between back office systems, extensions are the piece you will build.
Before your app can read or write anything, the merchant has to install it and approve its permissions. Shopify uses OAuth for this. The merchant grants the specific scopes your app asks for, such as reading orders or writing inventory, and Shopify issues an access token that authorizes each later request. The merchant stays in control and can uninstall the app to revoke access whenever they want.
Businesses reach for a Shopify integration when the unified online and in store data needs to reach further than Shopify goes on its own. A few situations come up repeatedly.
A merchant sells the same products online and in a shop, and maybe in a second shop too. Shopify already tracks inventory per location, but many businesses also run a separate warehouse system or a supplier feed. The integration keeps stock counts agreeing across Shopify and those outside systems, so the last unit sold at the counter is not also sold online an hour later.
Every order, tax line, and fee needs to reach the books. Rather than exporting spreadsheets, an integration reads orders from Shopify and creates matching entries in the accounting system automatically, grouped in whatever way your bookkeeper prefers. This removes a tedious manual step and reduces errors at month end.
Some retailers want the register to do something specific. Maybe staff need to see a customer's service history, apply a members only price, capture a custom field, or trigger a fulfillment action. A POS extension puts that behavior right on the checkout screen where the cashier works, without forcing them into a separate app.
If one of these matches what you are trying to do and you are unsure how large the effort is, a short call usually settles it. We are glad to look at your setup and give you a straight answer at no cost.
The real work in most integrations is keeping two systems in agreement as data changes on both sides over time. Shopify gives you the tools to do this well, but you have to use them deliberately.
You could ask Shopify on a schedule whether anything changed, but that is wasteful and slow. Instead, Shopify offers webhooks. You register a web address, subscribe to the events you care about, such as an order being created or inventory levels updating, and Shopify sends a message to your address the moment that event happens. Your software reacts immediately rather than waiting for the next poll.
We use webhooks for anything that should feel live, like inventory changes, and we keep a scheduled reconciliation job running in the background. Webhooks occasionally get missed if your server is briefly unavailable, so the scheduled job periodically compares Shopify against your other systems and repairs any differences it finds.
Webhooks keep the integration current. Reconciliation keeps it correct. Skip either one and you will feel it eventually.
Shopify can deliver the same webhook more than once. If your code assumes every message is new, you might process an order twice and throw off your books. The solution is idempotency, which means designing each handler so a repeated message produces no extra effect. Typically you record the event or order identifier and check whether you have already handled it before doing anything.
A few technical realities decide whether an integration stays healthy after launch. They are not complicated, but ignoring them leads to the failures that appear weeks or months later.
Shopify limits how much your app can request in a given window. With the GraphQL API, larger and more complex queries cost more against your allowance, so a request that pulls a huge amount of nested data counts more than a small one. The practical answer is to ask only for the fields you need, page through large data sets in reasonable chunks, and slow down politely when Shopify signals that you are approaching the limit. A well built integration treats this as normal, not as a crisis.
When your software creates or updates something in Shopify, you want a repeated request, perhaps caused by a network retry, to not create a duplicate. We design writes so they can be safely retried, tracking what has already been done so a second attempt corrects rather than duplicates. For anything touching orders or money, this discipline matters most.
Shopify lets developers create test stores where you can build and try the entire integration with sample products and test orders, without affecting a real business. You develop and verify every flow there first. Only when the behavior is correct do you install the app on the live store. Skipping this step is how avoidable mistakes reach real customers and real inventory.
Shopify updates its API on a regular schedule and expects apps to keep pace over time. An integration built and forgotten can break when an older version is retired. We build with this in mind and treat keeping current as part of ongoing care, not a surprise. Reconciliation routines help here too, giving you a scheduled check that everything still lines up.
Not every business needs custom software. The Shopify App Store is large, and many connectors already link Shopify to popular accounting tools, shipping providers, and marketplaces with minimal setup. If your needs match what one of those apps does, using it is usually faster and cheaper, and we will say so plainly.
Custom becomes the right choice when your process does not fit the standard mold. Signs you are past what a prebuilt app can handle include the following.
There is also a blended path. We often use an existing connector for the routine parts and build custom software only for the piece that truly needs it, so effort goes where it earns the most. If you cannot tell which category you fall into, that is exactly what a free scoping call is for.
Our process is intentionally plain because reliability comes from discipline. We start with the outcome you want, then work backward to the smallest, sturdiest connection that delivers it.
We are a Toronto studio, so we understand the local retail scene and the mix of tools merchants here tend to run beside Shopify. Throughout the project you deal with the people building it, not a ticket queue. When a decision comes up, we explain the tradeoff in plain terms and let you make the call.
The best integration is one nobody notices. Online and in store simply stay in agreement, and you get on with running the business.
Most integration trouble comes from a short, predictable list of mistakes. Knowing them in advance saves money down the road.
Webhooks are quick but not guaranteed. A team that assumes every event always lands, with no reconciliation, eventually hits a mismatch they cannot explain. Always pair live events with a scheduled comparison.
Because GraphQL query cost scales with how much you request, a careless query that pulls deep nested data burns through your rate allowance fast. Ask for only the fields you use and page through large sets in sensible chunks.
Without duplicate protection, a single retried request can create a phantom order or a double entry in your books. This is the kind of bug that erodes trust, so it belongs in the design from day one.
Shopify updates its API on a schedule, so an integration that is never maintained can break when an old version retires. We treat keeping current as part of ongoing care rather than a surprise repair.
At this point you have a good picture of the work and where the effort goes. The next step is usually a conversation about your specific systems, because the details of your accounting tool, your warehouse setup, or your checkout needs change the shape of the project. The FAQ below answers the questions we hear most, and after that we would honestly welcome a no cost call to look at your situation.
If you run Shopify and want it working with the rest of your business, or you want custom behavior at the register, the fastest way forward is to tell us what you are trying to accomplish. We will look at your setup, explain whether an off the shelf app or a custom build fits better, and give you an honest read on scope and timeline. There is no cost to ask and no obligation to proceed.
FourCents is a custom software studio in Toronto. We build integrations that keep online and in store in agreement and stay out of your way. Reach out for a free consultation and we will get you a clear answer quickly.
It is a software connection that ties Shopify into the rest of your operation, or that adds custom behavior at the register. It uses the Shopify Admin API to read and write products, inventory, orders, and customers, and POS extensions to change what happens at checkout.
The Admin API is how approved apps read and write a store's data. Shopify offers it as a GraphQL API, meaning you request exactly the fields you want in one call. That is efficient, but query size affects your rate allowance, so you ask only for what you need.
Through OAuth. The merchant installs the app and approves the specific scopes it requests, such as reading orders or writing inventory. Shopify issues an access token that authorizes each later request, and the merchant can uninstall to revoke access.
They add custom features to the Shopify point of sale app. An extension can show extra information on the cart screen, add a custom action a cashier can tap, or apply logic during checkout, so custom behavior lives right where staff ring up sales.
Yes. Shopify lets developers create test stores where you build and try the whole integration with sample products and test orders. We verify every flow there first, then install on the live store only once the behavior is correct.
Shopify can deliver the same webhook more than once. Idempotency means handling a repeated message without doing the work twice, usually by recording the event id and skipping anything already processed. It prevents duplicated orders and bookkeeping errors.
If an existing app does exactly what you need, use it. Custom makes sense when your rules are specific, when several tools must share the same Shopify data, or when you need register behavior only a POS extension can provide. We will tell you honestly which fits.
Yes. We are based in Toronto and know the local retail market, but we build Shopify integrations for clients regardless of location. The first consultation is free either way.