Build & Migrate
Shopify App Development
Private and public Shopify apps.
(opens in a new tab) When the App Store does not have it, we build it: private apps for one store, and public listings for brands taking a tool to market. We run a listed app of our own, so we build to Shopify’s review from the first commit.
The brands we build for, and the two we run ourselves.
Certified Partner The case for it
Why build a custom Shopify app
The App Store solves the common problems. It stops short when your fulfilment partner runs a bespoke API, or when three apps each do part of the job and none of them talk to each other. A private app replaces that stack with one piece of software you own.
We build private apps for UK and US merchants, and public listings for brands taking a tool to market. We run one of our own, too: Parity is a Shopify app we built and operate, which lets merchants edit their prices per market. Public apps ship with Shopify’s review requirements already met, so your listing does not stall waiting on approval.
The run of it
How we build a Shopify app
-
Should this be an app at all?
We start by checking whether an existing app, a script or a change of process already solves it. Building software you could licence for a monthly fee is a bad trade, and we will say so.
-
Scope and a fixed price
What the app does, where its data lives, which APIs it needs and whether it is private or public. You get a date and a number before we start, rather than an open meter.
-
Build against current API versions
Built and tested on a development store first. A public app is built to Shopify’s review requirements from the first commit, so approval does not turn into a second project.
-
Launch, then keep it current
A private app installs on your store; a public one goes through review. Shopify ships a new API version every quarter, so we flag deprecations before they break anything.
Build
Shopify app development agency
We build apps, and we run one of our own
Parity is a Shopify app we built and operate, listed on the Shopify App Store with Elms Agency as the developer. It puts every market for every product in one pricing grid, previews a bulk change before anything is written, and schedules sales that revert themselves.
Running it means we live with what we sell: Shopify’s review process, quarterly API versions, and merchants who expect a price change to be undoable. Every change Parity makes is logged with who ran it, and can be undone.
Custom Shopify app
Most of what we build never reaches the App Store
The bulk of our app work is private: integrations and custom features for stores we already build and look after. They install on one store, skip Shopify’s review queue and belong to the merchant who paid for them.
Black Sand shows the kind of brief that ends up there. It is an FMCG distributor, and we built a trade store where each buyer sees their own catalogue and their own prices. No theme does that out of the box, and logic like it belongs in the platform rather than in a theme somebody edits later.
Scope
What our Shopify app development covers
Inside your store
Private apps
Software for one store: the feature your catalogue needs, or the job three apps each do part of. Private, so it skips the review queue and nobody else can install it.
Shopify Functions and extensions
Discount, shipping and checkout logic that runs inside Shopify itself, where it belongs, rather than in a theme a future developer might break.
Between your systems
Integrations
Your fulfilment partner’s API, an ERP, a warehouse or a CRM connected to Shopify, with the sync rules agreed before anything ships.
Failure handling
Agreeing how a failed call is retried, and who finds out, before it goes live. Integrations fail quietly, so this is the part that matters most.
On the App Store
Public apps
A listing for brands taking a tool to market, built to Shopify’s review requirements from the start. We have been through that process with our own app.
Rescue and maintenance
Apps built by developers who have since moved on, read first and reported on honestly, then kept current as Shopify’s API versions change.
The honest comparison
A custom app, or one from the App Store?
The App Store is the right answer more often than an app developer will tell you. Here is where the two actually separate.
| Question | App Store app | Custom app |
|---|---|---|
| Time to live | Install it today | Weeks, depending on what it does and whether it needs review |
| Fit | Built for thousands of stores, so it does most of what you need | Does exactly the job, and nothing you do not use |
| Running cost | A monthly fee, and they compound as you add apps | Higher once, then maintenance |
| Bespoke systems | Only the ones its developer chose to support | Whatever API your partners run, including bespoke ones |
| Who it suits | A common problem that plenty of merchants share | A workaround burning real hours every week |
An app earns its cost when the workaround is burning real hours every week, or when an integration your business depends on has no off-the-shelf option. For a one-off problem, a script or a change of process usually beats commissioning software.
Not sure which apps are earning their fee? Start with a tech stack auditIntegrate
Knack Snacks
UK and US markets, subscriptions
Shopify app development
Three apps, built into the theme rather than bolted on
Not every brief needs a new app. Knack Snacks sell high-protein snacks in the UK and the US, and their store runs on apps that already exist: Loop for subscriptions, Judge.me for reviews, Smile.io for loyalty.
We built them into the theme rather than leaving each to render in the frame it ships with, and designed the subscription choice into the product page. Integrating a good app well is often a better buy than writing a new one.
Shopify app development company
The store, the tills and the systems behind them
Cream Cornwall sell luxury coastal homewares online and across three shops. We built the store on Horizon, ran the migration onto it, and set up Shopify POS in all three shops.
Stock, customers and orders have to agree between the website and the shop floor. That is where connections and custom features earn their keep, and it is why we still work with them as consultancy partner.
In their words
Reviews on the Shopify Partner Directory
Written by merchants, on Shopify's platform, where anyone can go and check them.
-
From start to finish, they were incredibly easy to work with. They understood the brief perfectly and delivered to a very high standard. Communication was excellent throughout, with quick and clear responses to any questions I had.
Tacky And Upsetting Store build or redesign · April 2026
-
The things [the team] have put in place and recommended for us have paid immediate dividend. We wish we had come in contact with [them] sooner.
ARTMARTIAL Store build or redesign · April 2026
-
I can’t recommend [the team] enough, [they] helped us with everything from product design, supplier communication to website building and SEO. We were able to build a brand off the back of all [their] information and help.
Reveliér Studios Business strategy guidance · April 2026
Buying it
How we work with you
Fixed-scope build
A private or public app, scoped and priced before we start, with a launch date. The usual shape when the brief is clear.
App rescue
An existing app that nobody dares touch. We read the code, tell you what condition it is in, and then fix, extend or replace it.
Developer days
A block of days with a named developer when you already know what needs building and only lack the hands.
Ongoing maintenance
Keeping an app current through Shopify’s quarterly API versions, so it does not stop working a year after launch.
Is this the right thing to buy from us?
Worth a conversation
A workaround is burning real hours every week, an integration your business depends on has no off-the-shelf option, or you are taking a tool of your own to the App Store.
Probably not us
A one-off problem, or one an existing app already solves for a monthly fee. A script or a change of process usually beats commissioning software, and we would rather point you at the existing product.
And we build on Shopify only. An app for another platform needs a specialist in that platform.
Same job, different words
What different people call this job
Agency, company, services, developer: the names differ and the job does not. Here is what to check whichever you search for.
Whether you search for a shopify app development agency, a shopify app development company or shopify app development services, the difference that matters is whether the people quoting have shipped through Shopify’s review process and whether they will still be reachable when the platform deprecates an API version. We have done both, on our own listing. Shopify custom development that stops at the point of handover is how a private app becomes the thing nobody dares touch.
Where this fits
Everything around a Shopify app project
More of what we build
The brands behind the stores we build and run.
Partners
Tools we have already run on our own stores
The apps around a Shopify store decide as much as the theme does, and choosing between thousands of them is most of the work. We are a Shopify Plus Partner and we integrate the tools that sit around the platform. Every one of them runs on our own two stores before it reaches a client, so the recommendation you get comes from having paid for the thing and lived with it. When a brand already runs a stack that works, we integrate with it rather than rebuilding it to suit us.
How we use them
Questions
Straight answers
What is the difference between a private and a public Shopify app?
A private app runs on your store alone and skips Shopify’s review queue. A public app lists on the App Store, goes through review, and can be sold to other merchants.
Can you fix a Shopify app we already have?
Yes, including apps built by developers who have since moved on. We start by reading the code and telling you what condition it is in.
Will the app keep working through Shopify API updates?
We build against current API versions and flag deprecations before they break anything. Shopify ships quarterly, so an app left alone for a year will need attention.
Do we actually need a custom app?
Not always, and we will say so. Building something you could licence for a monthly fee is a bad trade, and we would rather point you at the existing product.
How long does a Shopify app take to build?
It depends on what it does and whether it needs Shopify’s review. We scope and fix the price before starting, so you get a date and a number rather than an open meter.
Do you build apps for the Shopify App Store?
Yes. Public listings go through Shopify’s review, and we build to those requirements from the first commit so approval does not turn into a second project.
Start a conversation
Tell us what the workaround is costing you.
If an app already exists that does the job, we will tell you on the call rather than quote you for a new one.
UK and US brands buy this from the same senior team, and the American day is covered from the start of it rather than the end. How we work with US brands.
Get in touch