Shopify app development · New Zealand
Custom Shopify apps, built by a senior engineer.
Custom Shopify app development for merchants and agencies who have hit the edge of what off-the-shelf apps can do — private apps for your own store, public apps for the App Store, Shopify Functions, checkout extensions, and the Admin API and ERP integrations behind them. Written and owned by one senior developer.
In short
What a Shopify app developer actually builds
A Shopify app developer builds software that runs against Shopify’s APIs, not themes that style your storefront. That’s a custom (private) app installed on one merchant’s store to do something the App Store doesn’t; a public app listed on the Shopify App Store with OAuth, billing and a review process; Shopify Functions that change discounts, shipping and cart logic inside checkout; checkout UI extensions; and Admin API or Storefront API integrations that sync orders, inventory and customers with the systems you already run. If your problem is bespoke logic, an integration to your ERP or 3PL, or discount rules the platform can’t express, that’s app development — a job for a Shopify developer in New Zealand who writes code, not a theme customiser.
What we build
What custom Shopify app development covers
Most Shopify engineering work is one of these, or a few combined. If it touches the Admin API, checkout, or an external system, it’s in scope.
Custom (private) apps for your store
An app built for one store and installed straight from the Partner Dashboard — no App Store listing, no review queue. The right shape when the logic is specific to your business: internal tooling, a bespoke workflow, or an integration only you need.
Public apps for the App Store
A listed app with managed OAuth install, the Billing API for recurring charges, App Bridge and Polaris for an embedded admin, and the mandatory compliance webhooks — built to pass Shopify’s App Store review the first time rather than bouncing on it.
Shopify Functions
Custom discount, cart-transform, and delivery- and payment-customisation logic compiled to WebAssembly and run inside checkout. Functions are the supported replacement for the old Ruby Scripts, so pricing and bundling rules that used to live in Scripts get rebuilt properly.
Checkout & post-purchase extensions
Checkout UI extensions for Plus stores under checkout extensibility — custom fields, upsells, validation, banners — plus post-purchase and Thank-you / Order-status blocks. The modern path now that checkout.liquid is deprecated.
ERP, inventory & 3PL integrations
Two-way syncs between Shopify and the systems you run — Cin7, Unleashed, NetSuite, StarShipIT, a 3PL, or Xero — built on the Admin GraphQL API with webhooks and the Bulk Operations API, so stock, orders and fulfilment move on their own instead of by CSV.
Theme app extensions & headless
App blocks that drop into an Online Store 2.0 theme with no liquid edits, metafields and metaobjects for custom data, and — where a headless build earns it — a Storefront API front end on Hydrogen. The storefront layer, done as engineering.
In depth
How to think about a Shopify app build
Custom app or public app — which one you actually need
These are two different projects. A custom (private) app is built for a single store and installed directly from the Partner Dashboard: no App Store listing, no external review, no billing plumbing, and it can be as specific to your business as you like. A public app is a product — it’s listed on the App Store, has to handle OAuth install for any merchant, needs the Billing API, App Bridge and Polaris for an embedded admin, must implement the mandatory GDPR compliance webhooks, and has to pass Shopify’s review before it goes live. If only your store needs it, build a custom app; the public-app machinery is cost you don’t need. Build public when the app itself is the thing you’re selling and you want it in front of every merchant.
What Shopify Functions can and can’t do
Shopify Functions are how you change back-of-house logic — discounts, cart transforms, and delivery- and payment-method customisation — and they’re the supported replacement for the old Ruby Scripts, which are being retired. A Function is code (Rust or JavaScript compiled to WebAssembly) that Shopify runs synchronously inside checkout, so it’s fast and can’t be bypassed, but it’s deliberately sandboxed: no network calls, tight input and output, strict limits. That means a Function is perfect for “buy three, the cheapest is free” or a tiered trade discount, and the wrong tool when the rule depends on live data from an external system — that logic belongs in your app, with the Function reading a metafield the app has already set. Knowing which half goes where is most of the job.
Integrating Shopify with your ERP, inventory and 3PL
Most real Shopify work is integration, and the details decide whether it holds up. The Admin API is GraphQL-first now, with REST treated as legacy, and it’s rate-limited by calculated query cost on a leaky bucket — so a sync that works on a demo store falls over on a catalogue of thousands unless it’s written against the Bulk Operations API and paginated properly. Order and inventory changes come in over webhooks, which have to be verified and made idempotent because Shopify will retry them. Done right, Shopify talks to Cin7, Unleashed, NetSuite, StarShipIT or a 3PL, and to Xero for the accounting side, with stock levels, orders and fulfilment moving automatically. Done casually, you get duplicate orders, drifting stock, and a nightly job that silently stops.
When you don’t need a custom app
Plenty of the time you don’t, and a good Shopify developer will tell you so. If a well-supported App Store app already does the job — reviews, subscriptions, a standard loyalty scheme, email — install it; a monthly fee for something maintained by a full team beats commissioning a build you then own forever. If what you actually want is a nicer storefront, that’s theme work, not an app. And if a Shopify Function or a handful of metafields solves it, you don’t need a full public app to go with them. Custom app development earns its place when the gap is real: logic the platform can’t express, an integration to a system with no off-the-shelf connector, or a workflow specific enough that no listed app fits. If your problem isn’t one of those, I’ll point you at the cheaper answer.
Who you actually work with
Not an account manager in front of an offshore theme team — Isaac Vicliph, a senior software engineer with a decade shipping software in financial services, writing the app himself. Apps are built and delivered through the Shopify Partner Dashboard, so a custom app installs cleanly on your store and a public app is set up correctly for review. You get one accountable person from the first scoping call through App Store submission or install, direct contact throughout, and code on a mainstream stack you own outright. It’s a deliberately small studio: fewer projects, no junior hand-off, NZ-based and GST-registered.
How a Shopify project runs, and how it’s priced
Scope first, then a fixed price. The first conversation is about the actual problem — the discount logic Scripts can’t do any more, the ERP that won’t sync, the App Store gap you keep working around — and it ends in a written plan: custom app or public, which APIs and Functions, which integrations, what you own at the end, and one fixed price for that scope. A single Function or a focused custom app is a far smaller job than a public App Store product with billing and review, so rather than publish a number that’s wrong for your build, I quote once I understand it. No hourly meter, no estimate that drifts. Tell me what the store needs to do and you’ll get a straight plan and a straight price back.
Reviewed July 2026 · written by Isaac Vicliph, Tally Digital
Questions
Frequently asked
What does a Shopify app developer do?
Builds software that runs against Shopify’s APIs rather than styling your storefront: custom (private) apps for a single store, public apps for the App Store, Shopify Functions for checkout logic, checkout extensions, and Admin or Storefront API integrations with your ERP, inventory, 3PL or Xero. It’s engineering, not theme customisation.
What’s the difference between a private and a public Shopify app?
A custom (private) app is built for one store and installed straight from the Partner Dashboard — no listing, no review, and it can be as specific to your business as you need. A public app is a product listed on the App Store: it handles OAuth install for any merchant, needs the Billing API and an embedded admin, must implement the compliance webhooks, and has to pass Shopify’s review. Build custom when only your store needs it.
What are Shopify Functions and can you build them?
Yes. Shopify Functions are custom discount, cart-transform, and delivery- and payment-customisation logic compiled to WebAssembly and run inside checkout — the supported replacement for the retired Ruby Scripts. They’re fast and sandboxed, so business rules that depend on external data live in your app and set a metafield the Function reads. Rebuilding old Scripts as Functions is common work.
Can you integrate Shopify with our ERP, inventory or 3PL?
Yes — that’s most of the work. Two-way syncs with Cin7, Unleashed, NetSuite, StarShipIT, a 3PL, or Xero, built on the Admin GraphQL API with verified webhooks and the Bulk Operations API so it holds up on a real catalogue. Orders, stock and fulfilment move automatically instead of through CSV exports.
How much does a custom Shopify app cost in New Zealand?
It depends entirely on scope — a single Shopify Function or a focused custom app is a very different job from a public App Store product with OAuth, billing and review, so a blanket price would mislead. I scope your actual requirement first, then give you a fixed price for that scope before any work starts. Tell me what the store needs to do and you’ll get a firm number back.
Do I need a custom app, or will an App Store app do?
Often an App Store app is the right call and I’ll say so — a maintained monthly app beats a custom build you own forever when it genuinely fits. Go custom when the gap is real: logic Shopify can’t express, an integration with no off-the-shelf connector, or a workflow too specific for any listed app. If a Function or a few metafields solves it, you don’t need a full app either.
Can you build and submit a public app to the Shopify App Store?
Yes. Public apps are built through the Partner Dashboard with managed OAuth install, the Billing API for recurring charges, App Bridge and Polaris for the embedded admin, and the mandatory compliance webhooks — set up to pass Shopify’s App Store review rather than bounce on it. I can build for listing or build a custom app for your store alone.
Are you a Shopify developer or a Shopify agency?
A senior software engineer who builds Shopify apps and integrations — not a theme shop and not a monthly marketing retainer. You talk to the person who designs and writes the code, every time, and the app runs on a mainstream stack you own outright.
Tell me what your Shopify store can’t do yet.
The discount logic the platform won’t express, the ERP that won’t sync, the App Store gap you keep working around — tell me what the store needs to do and I’ll scope the smallest app that does it, then come back with a clear plan and a fixed price.