The Shopify App Store has over 8,000 apps. For most problems a merchant faces, something exists. But there are genuine cases where a custom-built Shopify app is the right answer — and getting this decision wrong in either direction costs significant money. This guide lays out the honest framework for making it.
Custom vs Private vs Public App: The Differences
| App Type | Who It Is For | Distribution | Installation | OAuth Required |
|---|---|---|---|---|
| Custom App | Single store, specific need | Not distributed | Direct via admin token | No |
| Private App (legacy) | Single store (deprecated model) | Not distributed | Legacy token method | No (legacy only) |
| Public App | Multiple merchants | App Store or direct link | OAuth install flow | Yes |
For most merchants building bespoke functionality for their own store, a custom app is the correct choice in 2026. Private apps were deprecated by Shopify and replaced by the custom app model. Public apps make sense only if you intend to sell or distribute the functionality to other merchants.
Build vs Buy Decision Framework
Start with the App Store. Before committing to custom development, search thoroughly, trial the leading options, and evaluate: does it integrate with your existing stack? Is it actively maintained? Can it scale to your order volume? Does the vendor have a track record?
Build when: no existing solution fits your workflow without significant compromise; you have a proprietary process that is a competitive advantage and should not be replicated by app vendors; the ongoing app subscription cost at scale exceeds the development cost within 12–18 months; or you need deep integration with internal systems (ERP, WMS, PIM) that requires custom API work regardless.
Do not build when: a £20/month app does 90% of what you need; your requirements are likely to change significantly within 12 months; you do not have the internal resource to maintain custom code long-term.
Development Cost Estimates
Custom Shopify app costs vary considerably by complexity. Honest benchmarks from 2026 agency rates in the UK:
- Simple custom app (single-purpose, e.g. custom fulfilment trigger, basic product sync): £5,000–£15,000
- Mid-complexity app (embedded app with admin UI, Shopify Functions, webhook processing): £15,000–£40,000
- Complex integration app (ERP/WMS sync, real-time inventory, multi-system orchestration): £40,000–£150,000+
These ranges assume a competent agency or senior freelancer. Offshore development at lower rates typically increases project duration and QA overhead, often eroding the cost saving.
Timeline Expectations
Simple apps can go from brief to live in four to six weeks if requirements are clear. Mid-complexity apps typically take eight to sixteen weeks including requirements, development, testing, and deployment. Complex integrations involving ERP vendors and phased rollouts run to four to twelve months. These timelines assume prompt client feedback and access to third-party API documentation and credentials from day one.
For scoping a custom Shopify app, OneOnic’s Shopify development team can review your requirements and provide a detailed brief and cost estimate before any commitment.
Common Custom App Use Cases
The most common reasons merchants commission custom Shopify apps: proprietary ERP integration where no standard connector exists; custom fulfilment logic routing orders to multiple 3PLs based on complex rules; bespoke loyalty or reward mechanics not covered by existing apps; specialised B2B ordering portals built on top of Shopify’s B2B APIs; and internal tools that pull Shopify data into operational dashboards.
Frequently Asked Questions
Do I own the code for a custom Shopify app?
Ownership depends on your contract with the developer. Standard agency practice in the UK is to transfer full intellectual property of the delivered code to the client on final payment. Always confirm IP ownership in writing before work begins. Ensure you also receive access to all repositories and deployment credentials at project close.
Can a custom app access all Shopify data?
A custom app’s data access is determined by the API scopes you request when creating it in the Shopify admin. You can grant access to orders, products, customers, inventory, fulfilment, metafields, and more — each as a separate read or write permission. Apps only have access to data within the store they are installed on; they cannot access data from other Shopify stores.
What happens if the developer who built my custom app is no longer available?
This is a genuine operational risk with custom software. Mitigate it by: ensuring the code is in a repository you own and control, requiring documentation of the app architecture and deployment process, avoiding proprietary frameworks or unusual dependencies, and maintaining a relationship with an agency (rather than a single freelancer) where continuity is built in.
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