Custom Shopify Apps: When to Build One, and When to Install One

The Shopify App Store has an app for almost everything, and for most stores, most of the time, installing one is the right answer. It is cheaper, it is maintained by someone else, and it is running by the afternoon.

The question worth asking is when that stops being true. Here is how we tell.

Five signs a custom app is worth it

1. You are running three apps to do one job. A subscription app, a loyalty app and a spreadsheet, stitched together with a Zap, to do something that is one process in your business. Every app is another monthly fee, another script on the storefront and another thing that can break when one of them updates.

2. Someone is doing it by hand every day. Exporting orders to an ERP, updating stock from a supplier file, tagging customers for wholesale pricing. If a person is copying data between Shopify and another system on a schedule, that is an integration waiting to be written.

3. The logic is specific to your business. Pricing rules, eligibility, allocation or fulfilment logic that no public app models because no other store needs it. Public apps are built for the common case, and a business whose edge is the uncommon case will spend its life fighting their settings.

4. You need your data to stay yours. Some apps hold your customer or order data in their own systems, on their terms. A custom app keeps the logic and the data in places you control.

5. It is the product, not a feature. When the thing you are building is what you sell, it should not depend on a third party’s roadmap.

If none of those apply, install the app.

What a custom app can touch

A custom app uses the same building blocks as any app on the App Store:

• The Admin API, to read and write products, orders, customers, inventory and fulfilment.
• Webhooks, so the app reacts when an order is placed or stock changes, rather than polling.
• Admin extensions, putting the app’s screens and actions inside the Shopify admin your team already uses.
• Checkout and account extensions, adding fields, content and logic to checkout and the customer’s order pages.
• Shopify Functions, custom discount, delivery and payment rules running inside Shopify itself.

Two of those depend on your plan. Custom apps containing Shopify Functions are only available on Shopify Plus, and so are checkout UI extensions on the information, shipping and payment steps. Extensions on the Thank you and Order status pages work on every plan. If the idea for your app lives inside checkout, check the plan first. Shopify Scripts, the older Plus mechanism for checkout logic, stopped running on 30 June 2026, so Functions are now the only route.

Build on GraphQL. Shopify made the REST Admin API legacy in October 2024, and from April 2025 new public apps have had to use GraphQL only. A custom app is not bound by the App Store rule, but REST is not where new capability is going.

What we built for LOOP

LOOP is a marketplace for ethical e-gift cards, where customers buy from many conscious brands without leaving the site. Our research showed most of the brands LOOP wanted to sign already sold on Shopify, so asking them to adopt another admin to manage their LOOP sales would have slowed every signing.

So we built a Shopify plugin instead. Partner brands track their LOOP sales and redemptions in real time from a dashboard inside their own Shopify admin. The integration meets them in the tool they already use every day, which is the whole argument for a custom app in one example: the logic was specific to LOOP’s business, and no public app did it.

What it costs to own one

The build is the visible cost. Ownership is the one people miss.

API versions move every quarter. Shopify releases a new API version quarterly and supports each for at least twelve months. A custom app needs a small amount of work every year to stay on a supported version. It is routine if it is planned, and a scramble if it is not.

Hosting, if it has a backend. Many custom apps run their own server for logic and storage. That is a small monthly cost and something that needs monitoring.

Someone who knows it. An app written by a contractor who has since moved on is a liability the first time it needs changing. Documentation, access in your own accounts, and code in your own repository are not optional extras.

None of this is a reason not to build. It is a reason to build only what earns it, and to budget for year two before approving year one.

Where to start

Write down the job, in business terms: “stock from our supplier’s file updates Shopify every hour”, “wholesale customers see their contract price”. Then look for an app that does exactly that. If one does, install it. If the closest match needs a workaround, or three apps, that list is your custom app’s specification.

Three of our developers hold Shopify certifications, and building on the current platform, Functions, extensions and GraphQL, is where that matters most. More on our Shopify development work and Shopify Plus.

---

Sources: Shopify: apps in checkout, About Shopify Functions, and new public apps must use GraphQL from April 2025 (Shopify developer changelog).