Difference Between Shopify Public Apps vs Custom Apps vs App Extensions?

In Shopify, these three concepts are related but not the same thing:

Concept	What it is	Main purpose
Public App	An app built for many Shopify merchants	Sell/distribute your app to merchants
Custom App	An app built for one specific store/business	Solve a specific merchant's needs
App Extension	A feature/component that extends Shopify's existing admin, checkout, POS, etc.	Put your app's functionality inside Shopify

1. Public Apps

A public app is an app that you build so that multiple Shopify merchants can install and use it.

For example, imagine you build an app called "Smart Product Bundles".

A merchant installs it from the Shopify App Store, gives it the required permissions, and uses it to create product bundles.

Typical characteristics:

• Designed for many merchants
• Can be distributed through the Shopify App Store
• Usually has an installation/authentication flow
• You build a reusable product rather than something for one store
• Can potentially become a SaaS business

Example:

You build an AI product-description generator → thousands of Shopify stores install it → each merchant pays you monthly.

That's a public app.

2. Custom Apps

A custom app is built for a specific Shopify store or organization, rather than being a general-purpose product for everyone.

For example, a company has a Shopify store and asks you:

"We need an app that automatically sends our orders to our internal warehouse system."

You build an app specifically for that company's workflow.

Typical characteristics:

• Intended for a specific merchant/store
• Not designed as a general App Store product
• Can access Shopify APIs according to the permissions it is granted
• Useful for integrations and internal business processes

Example:

Shopify Store
     ↓
Custom App
     ↓
Company's ERP / Warehouse System

So if one company hires you to integrate Shopify with its internal software, a custom app is often the appropriate approach.

3. App Extensions

An app extension is different.

It isn't necessarily a complete app by itself. Instead, it lets you add your app's functionality into specific parts of Shopify.

Think of it as:

App = the overall application Extension = a feature/component of that application that appears inside Shopify

For example, you could build an app that adds a custom feature to the Shopify admin.

Instead of forcing the merchant to leave Shopify and open your app, your functionality can appear directly in an appropriate Shopify surface.

Some extension areas include:

• Admin
• Checkout
• Shopify POS
• Customer accounts
• Online Store
• Shopify Flow, and others

For example:

                    
                        Your Shopify App
                              │
          ┌───────────────────┼───────────────────┐
          ↓                   ↓                   ↓
    Admin Extension	  Checkout Extension     POS Extension
                   

The important relationship

A common misconception is:

"Public app vs custom app vs app extension are three competing types of apps."

Not exactly.

Public vs custom describes who the app is intended for/distributed to.

App extension describes how your app integrates its functionality into Shopify's platform surfaces.

So you can have something like:

Public App
   │
   ├── Admin Extension
   ├── Checkout Extension
   └── POS Extension

And a custom app can also use appropriate Shopify extension mechanisms where supported.

Simple analogy

Imagine Shopify is an operating system:

• Public App → an application you publish for many users
• Custom App → an application built for one particular customer
• App Extension → a plugin/component that inserts functionality into specific parts of the platform

For a Shopify developer

If you're learning Shopify app development, I'd think about them in this order:

1. Learn how to build a Shopify app → authentication, Shopify APIs, database, frontend/backend, webhooks.

2. Understand distribution → public app vs custom/internal use case.

3. Learn App Extensions → when you want your app's functionality to appear directly inside Shopify Admin, checkout, POS, etc.

The key distinction to remember is:

Public/Custom = who the app is for.
Extension = where/how the app's functionality appears in Shopify.