# Shopify App Development UK: Custom Apps and Shopify Functions

Source: https://dijituldevelopments.co.uk/shopify-app-development/
Updated: 2026-11-11

> dijitul developments builds custom Shopify apps for UK merchants: private apps for one store, Shopify Functions for discounts, delivery and payment rules, checkout UI extensions on Shopify Plus, and integrations through the Admin GraphQL API and webhooks. We also replace retired Shopify Scripts and checkout.liquid code. Every project is a fixed-price quote after a free chat.

## Problems this solves

- Your Shopify Scripts stopped working on 30 June and the discounts or shipping rules went with them
- Tracking or upsell code on the order status page vanished when Shopify retired additional scripts
- No public app does the one thing your business needs, or it does it badly with a monthly fee per feature
- Orders, stock and customers have to be copied between Shopify and your ERP or warehouse system
- An old app still uses a static access token and nobody knows who created it
- A theme app relies on script tags that Shopify is phasing out

## Key facts

- Shopify's changelog says new custom apps cannot be created in the Shopify admin after 1 January 2026; they are made in the Dev Dashboard
- Dev Dashboard apps use OAuth flows such as client credentials or token exchange rather than a static admin token
- Shopify Scripts stopped running on 30 June 2026; Shopify Functions replace them
- Shopify's docs say only Plus stores can use custom apps containing Function APIs; public apps with functions work on any plan
- Checkout UI extensions on the information, shipping and payment steps are Shopify Plus only
- Thank you and Order status page extensions are available on all plans except Starter, per Shopify's docs
- Shopify says storefront script tags cannot be created or updated after 1 October 2026 and stop running on 1 March 2027

## Custom apps: what has changed in 2026

A custom Shopify app is one built for a single store, not listed on the Shopify App Store. It is the right choice when a public app does not fit your process or charges monthly for something you could own outright.

The way these apps are created changed this year. Shopify's changelog says that from 1 January 2026 you can no longer create new custom apps in the Shopify admin. Existing ones keep working, but new custom apps are created and managed in the **Dev Dashboard** with custom distribution to one store. Shopify's developer community notes these apps do not display a static Admin API access token; they authenticate with OAuth flows such as client credentials, token exchange or authorisation code grant. That is better security, but it means any integration copied from an old tutorial needs reworking.

We build apps in TypeScript with Shopify CLI, using the Admin GraphQL API, which is where Shopify puts new capabilities. Shopify releases a new API version every quarter, so we pin versions and plan upgrades rather than waiting for something to break.

## Shopify Functions: the replacement for Scripts

Shopify Scripts were the Ruby snippets Plus merchants used for custom discounts, shipping and payment rules. Shopify's migration guide says editing and publishing new Scripts ended on 15 April 2026 and all Scripts stopped running on 30 June 2026. If your store relied on them, those customisations are now off.

**Shopify Functions** replace them. A Function is a small piece of code, usually Rust or JavaScript compiled to WebAssembly, that Shopify runs inside its own infrastructure at a defined point. Function APIs cover:

- **Discounts**: tiered, bundle, customer-tag or quantity-break pricing.
- **Delivery customisation**: hide, rename or reorder shipping options, such as no next-day delivery for oversized items.
- **Payment customisation**: hide cash on delivery above a value, or offer invoice terms to trade customers only.
- **Cart and checkout validation**: block orders that break business rules, such as minimum trade quantities.

One licensing point from Shopify's docs: any plan can use public apps that contain Functions, but only Shopify Plus stores can use *custom* apps that contain Function APIs. If you are not on Plus, we look for a public app that does the job or discuss whether Plus is justified.

## Checkout and post-purchase pages

Shopify has retired checkout.liquid and additional scripts. Shopify's developer docs say script tags on the Thank you and Order status pages were sunset on 28 August 2025 for Plus stores and on 26 August 2026 for other stores. The replacements depend on what the old code did:

- **Visual content**, such as upsells, surveys or delivery notes: **checkout UI extensions**. Shopify's docs say extensions on the information, shipping and payment steps are Plus only, while Thank you and Order status extensions are available on all plans except Starter.
- **Tracking and analytics**: **web pixel extensions**, which run in a sandbox and work on any plan but cannot show UI.
- **Branding**: checkout branding settings and the Admin GraphQL API's branding types.

A separate deadline is coming for storefronts: Shopify says apps cannot create or update storefront script tags after 1 October 2026, and those tags stop running on 1 March 2027. Theme app extensions are the replacement, and we can audit which of your apps still depend on script tags.

## Integrations: Shopify and the rest of your business

Many custom apps are really integrations: orders into Sage, Xero or an ERP, stock levels in from a warehouse system, customers out to a CRM. We build these on the Admin GraphQL API with bulk operations for large catalogues, and webhooks for orders, refunds and inventory, verified by HMAC signature and processed through a queue so a slow downstream system never loses an order. Rate limits are handled by GraphQL query cost rather than guesswork. See Shopify integration and ecommerce to ERP integration for the patterns. If you are also thinking about selling through AI assistants, see agentic commerce integration.

## How a Shopify app project runs

We start with a free chat about what you need the store to do and what currently breaks. Scoping lists the Functions, extensions and integrations, confirms which need Shopify Plus, and checks whether an existing public app already does the job well enough. You get a fixed-price quote. We build against a development store first, then install on yours with custom distribution. You own the code. We have built ecommerce extensions since our OpenCart, CubeCart and WP e-Commerce days, and the habits carry over: test the edge cases, keep the shop running during changes, and document everything. For theme and store build work rather than apps, see Shopify development.

## What we deliver

- A custom app in the Dev Dashboard with custom distribution to your store
- Shopify Functions for discounts, delivery customisation, payment customisation or cart and checkout validation
- Checkout UI extensions, on Plus, and Thank you and Order status page extensions
- Web pixel extensions to replace tracking that ran in additional scripts
- Admin GraphQL API integrations with webhooks verified by HMAC signature
- Theme app extensions instead of script tags
- Hosting, monitoring and an upgrade plan for Shopify's quarterly API versions

Technologies: Shopify Functions, Admin GraphQL API, Checkout UI extensions, Shopify CLI, TypeScript, Rust, WebAssembly, Webhooks

## FAQs

### Can we still create a custom app in the Shopify admin?

No. Shopify's changelog says new custom apps cannot be created in the admin after 1 January 2026. Existing ones keep working, but new custom apps are created in the Dev Dashboard with custom distribution to your store. dijitul developments sets these up and handles the OAuth authentication they now require.

### Our Shopify Scripts stopped working. What now?

Shopify Scripts stopped running on 30 June 2026. Their discount, shipping and payment logic is rebuilt as Shopify Functions. dijitul developments maps each old Script to the right Function API, builds and tests it on a development store, then deploys it. Custom apps with Functions need Shopify Plus.

### Do we need Shopify Plus for a custom app?

Not for every custom app. Integrations, admin tools and Thank you page extensions work on standard plans. Shopify's docs say custom apps containing Function APIs, and checkout UI extensions on the information, shipping and payment steps, need Shopify Plus. dijitul developments confirms which parts of your plan need it.

### Our order status page tracking disappeared. Can you fix it?

Yes. Shopify retired additional scripts and script tags on the Thank you and Order status pages, on 28 August 2025 for Plus and 26 August 2026 for other plans. Tracking moves to web pixel extensions and visible content to checkout UI extensions. dijitul developments rebuilds both.

### Custom app or public app from the App Store?

If a well-supported public app does the job, it is usually cheaper. A custom app makes sense when your process is specific, when you would otherwise stack several paid apps, or when data must flow to your own systems. dijitul developments checks the App Store first during scoping.

### How is Shopify app development priced?

dijitul developments gives a fixed-price quote after a free chat and a scoping stage that lists the Functions, extensions and integrations needed and which require Shopify Plus. Hosting for any app backend and ongoing API version upgrades can be covered by a support agreement.

## Pricing and contact

Every project gets a fixed-price quote after a free initial chat and a short scoping stage. You own the code and the data. Book a free chat: https://dijituldevelopments.co.uk/contact/ · 01623 650333 · info@dijitul.uk