Shopify app developer for custom apps, integrations and checkout

If your store needs something that neither your theme nor an App Store app can do, you need a Shopify app developer. I build custom Shopify apps, integrations with ERP, accounting and CRM systems, Checkout UI extensions and Shopify Functions for merchants whose operations have outgrown the standard set-up. I don't do theme design. This is engineering work on the parts of Shopify behind the storefront.

This page explains what a custom app can do, when you need one, how an engagement works and what to prepare. The guides linked below go deeper into each type of work.

What a custom app can do that themes and public apps can't

A theme controls how the storefront looks. A public app from the Shopify App Store solves a common problem for thousands of stores at once. A custom app is built for one store and does exactly what that store needs. In practice that means:

• Move data between Shopify and your other systems the way your business actually works. Orders go to the ERP with your own mapping for tax codes, locations and customer accounts. Inventory comes back from the warehouse system. Refunds and payouts reach the accounting system in a form your finance team can reconcile.
• Change checkout logic with Shopify Functions: discount rules that the native discount types can't express, hiding or renaming delivery and payment methods by customer, cart or market, validating a cart before an order is placed, and building bundles.
• Add UI to checkout and post-purchase pages with Checkout UI extensions: custom fields, delivery instructions, B2B purchase-order inputs, loyalty balances, and content on the Thank you and Order status pages.
• Extend the Shopify admin with admin actions and blocks, so staff can run your processes from the order or product page instead of a spreadsheet.
• Model your data properly with metafields and metaobjects, so specifications, compatibility tables, contract prices or production details live in Shopify and are available to the theme, checkout and Functions.
• Automate the jobs that eat staff time: bulk updates through the GraphQL Admin API's bulk operations, scheduled jobs, and event-driven workflows triggered by webhooks.

What a custom app is not: a way around Shopify's limits. Checkout, payments, tax calculation and the order model are owned by Shopify. A good developer tells you early when a requirement fights the platform, and what the closest supported option is.

When you need a custom app, and when you don't

You probably don't need custom development if an App Store app already does 90% of what you need and the remaining 10% is a preference, not a business rule. A well-supported public app gets updates, security fixes and new Shopify features without you paying for them. Try that first.

You probably do need a custom app when:

• you have tried two or three connectors and each one breaks on the same edge case: partial refunds, bundles, multi-location stock, B2B pricing, split shipments or foreign currency;
• the data mapping is specific to your business, such as your chart of accounts, your ERP's item codes or your CRM's lifecycle stages;
• you are paying for several apps that each do a slice of one workflow, and they fight each other;
• you need checkout or discount logic that isn't a setting anywhere;
• you are moving off Shopify Scripts, checkout.liquid or script tags and need the replacement built properly;
• you need an audit trail: which order was sent where, when, and what the other system replied.

If you are thinking of building a public app to sell on the App Store, read build a Shopify app yourself or hire a developer first.

What I build

• IntegrationsHow Shopify integrations with NetSuite, QuickBooks, Xero, HubSpot, Salesforce, Amazon, ERPs and AI services work, when a connector is enough, and when you need a custom integration app.
• CheckoutHow Shopify checkout is customized today: Checkout UI extensions, Shopify Functions, branding, and Thank you and Order status pages, with plan requirements and when a no-code app is enough.
• Shopify FunctionsWhat Shopify Functions are and what they can do: discount functions, cart transform, delivery and payment customization, cart and checkout validation. How they're built, plan requirements, limits, and example code.
• MigrationsMigrating to Shopify from Magento, WooCommerce, BigCommerce, Wix, Squarespace, WordPress or another Shopify store: what migration tools handle, what they don't (redirects, customer accounts, subscriptions, custom data, custom features) and a launch checklist.
• Shopify B2BWhat Shopify B2B includes on each plan since April 2026, how companies, catalogs, volume pricing, payment terms and purchase orders work, and which B2B requirements need a custom Shopify B2B app or ERP integration.
• Shopify Plus developmentWhat Shopify Plus merchants actually need developers for (checkout extensibility, Functions, B2B, Launchpad and Flow automations, expansion stores, ERP integration) and how to choose between an agency and a specialist developer.

How custom Shopify app development works

Every engagement follows the same five steps. The aim is that you know what you are getting and what it costs before any code is written, and that you can run the result without me afterwards.

1. Discovery

A conversation about the problem, not the solution. What happens today, who does it, where it breaks, which systems are involved and what "done" looks like. For integrations I ask for sample records from both sides, such as a few real orders, a refund and an invoice. The awkward cases are where the work is.

2. Scope

A written scope: what the app will do, what it won't do, which Shopify APIs and extensions it uses, what plan requirements apply, where data is stored, how errors are handled and reported, and how we will test it. The quote or estimate is based on this document. If something is uncertain, such as an undocumented ERP API, the scope says so and plans a small proof of concept first.

3. Build

The app is built with Shopify's current stack: Shopify CLI, the GraphQL Admin API, webhooks, and app extensions and Functions where they are needed. Work happens on a development store or a copy of your data first. You get regular, short progress updates with something you can click on, not just status reports.

4. Review

You test against real scenarios on a development store and then on your live store in a controlled way, for example with a feature flag, one location or one customer group first. Integration work includes a reconciliation check: do the totals in Shopify match the totals in the other system for the test period?

5. Hand-over

You get the repository, deployment and hosting on accounts you own, environment documentation, a runbook for the likely failure modes ("the ERP was down for an hour, what now?"), and a walkthrough with whoever will maintain it. Ongoing support is available if you want it, but it is not required. The app should not need me to keep running.

What to prepare before you get in touch

You don't need a specification. These help, though:

1. The problem in one paragraph, in business terms. "Our finance team spends two days a month matching Shopify payouts to Xero" is better than "we need a Xero API integration."
2. The systems involved, with versions and editions where they matter: for example NetSuite with or without SuiteCommerce, QuickBooks Online or Desktop, Dynamics 365 Business Central or Finance & Operations.
3. Your Shopify plan, number of stores, markets and locations. These decide which options are even available.
4. Volumes: orders per day at peak, number of SKUs and variants, and number of B2B customers or price lists.
5. Examples of what goes wrong today, such as screenshots, exported records or a list of failed syncs.
6. Who on your side owns the process and can answer questions about it.

What I don't do

To save us both time:

• Theme design and storefront builds. I don't design or build themes. For that you want a theme designer or a Shopify agency.
• Marketing, SEO campaigns, ads and conversion-rate consulting.
• Work that needs a workaround Shopify doesn't support, such as scraping checkout, injecting scripts into checkout, or bypassing platform limits. It breaks, and it can put your store at risk.

Plan requirements worth knowing up front

Most custom apps work on every Shopify plan. Two exceptions shape a lot of projects:

• Custom apps that contain Shopify Functions can only be used on Shopify Plus. Public App Store apps that contain Functions work on any plan.
• Checkout UI extensions on the information, shipping and payment steps are available only on Shopify Plus. Extensions on the Thank you and Order status pages work on all plans.

Also note that since January 1, 2026, new custom apps can't be created from the Shopify admin. They are created in Shopify's Dev Dashboard and then installed on your store. Existing admin-created apps keep working.

Guides

If you want to understand the options before talking to anyone, start here:

• How to build a Shopify app, or when to hire a developer instead
• Shopify integrations: NetSuite, QuickBooks, Xero, ERPs and more
• Checkout customization and Checkout UI extensions
• Shopify Functions, and migrating from Shopify Scripts
• Store migrations: the parts migration tools don't handle
• Shopify B2B and wholesale
• Shopify Plus development