Shopify Custom App vs Public App: When It Pays to Build Your Own

Every few weeks a store owner asks me the same thing: “There’s an app for this, but it costs $X a month and only does half of what we need. Should we just build our own?” Sometimes the answer is yes. Often it’s no. The difference comes down to a few questions you can answer before anyone writes code.

This guide covers what a Shopify custom app actually is, when custom app development pays for itself, and when an off-the-shelf app from the App Store is the smarter call.

Custom app vs public app: the short version

A public app is what you install from the Shopify App Store. One developer builds it for thousands of stores, Shopify reviews it, and you pay a monthly fee (or a usage fee) for as long as you keep it.

A custom app is built for one store, or one group of stores you own. It isn’t listed in the App Store. It’s installed from a private link, it does exactly what your store needs, and nobody else can install it.

When a custom app pays for itself

1. You’re paying for three apps to do one job

This is the most common case I see in app audits. One app tags orders, another sends them to the warehouse, a third posts low-stock alerts to Slack. Each one is cheap on its own. Together they cost real money every month and still need someone to babysit the gaps between them. One small custom app, or one automation, can replace all three.

2. The workflow is the thing that makes your business different

Public apps are built for the average store. If your edge is something unusual (made-to-order products, trade pricing by customer group, a quoting step before checkout, a subscription model that doesn’t fit the subscription apps), you’ll spend more time fighting a generic app than you would building the right one.

3. You need data to move between Shopify and a system nobody else uses

An ERP your supplier set up in 2014. A local courier with its own API. A warehouse that wants CSV files on an FTP server at 6am. No public app connects to these, because there aren’t enough stores using them to justify it. A custom app (or an n8n workflow calling the Shopify API) does it reliably.

4. The monthly fee keeps climbing with your order volume

Many apps charge by orders, contacts or usage. That’s fair when you’re small. At scale, you can end up paying more each year for the same feature. Here’s the simple test: take the build quote and divide it by the monthly fee you’d cancel. If the answer is under 12 to 18 months and the feature isn’t going to change much, building usually wins.

Example: if a custom build is quoted at 10 times the monthly fee of the apps it replaces, it pays back in 10 months. After that, you’re only paying for hosting and occasional updates.

When you should NOT build a custom app

• A good public app already does 90% of it. Reviews, email marketing, subscriptions and loyalty are hard problems that big teams solve full-time. Pay for the good app.
• You’re not sure the process will last. If you’re still testing whether a feature sells, rent it from an app first. Build once you know it works.
• Nobody will look after it. Shopify releases a new API version every quarter and retires old ones. A custom app needs someone to keep it current. If you don’t have a developer you can call, factor that in.
• It’s really a theme change. Sticky add-to-cart bars, size charts, FAQ tabs and trust badges don’t need an app at all. They’re a few lines of Liquid and CSS in your theme.

What goes into Shopify custom app development

A typical build looks like this:

1. Scope. Write down exactly what the app should do, what triggers it, and what “done” looks like. Most budget overruns start here, not in the code.
2. Access. The app is set up for your store and given only the permissions it needs (orders, products, customers, and so on).
3. Build. Usually a small server that listens for Shopify webhooks (new order, product updated, customer created) and calls the Shopify API. If staff need a screen inside the Shopify admin, an embedded admin page is added.
4. Storefront pieces, if any. Anything customers see goes in through a theme app extension, so it can be switched on and off from the theme editor instead of being pasted into your code.
5. Testing on a development store before it touches real orders.
6. Handover. You should get the code, the hosting login and a short document explaining what it does. If a developer won’t give you the code, that’s a red flag.

One limit to know about: if your idea needs Shopify Functions (custom discount rules, checkout validation, shipping or payment rules), a custom app with Functions only runs on Shopify Plus. On other plans, you’d need a public app that offers that function.

Custom app or automation?

Not every “custom app” needs to be an app. If nothing needs to show up inside the Shopify admin or on your storefront, and the job is “when X happens, do Y in another system”, an automation tool is often faster and cheaper to run. I cover five of those in Shopify + n8n automations every DTC brand needs.

Build an app when staff need a screen in Shopify, when customers need to see something new on the storefront, or when the logic is complex enough that you want it in proper version-controlled code.

A quick decision checklist

• Is there a public app that does at least 90% of what you need? Use it.
• Are you paying for two or more apps that each do part of one job? Consider building.
• Does the build pay back in under 18 months against the fees you’d cancel? Consider building.
• Does it need to talk to a system no public app supports? Build, or automate.
• Will someone maintain it after launch? If not, don’t build yet.

If you want a second opinion, I’ll look at your current apps and the job you’re trying to do, and tell you plainly whether a custom Shopify build, an automation, or an existing app is the right fit.