Shopify App Development Agency

Shopify app development by a team that ships its own apps

Custom Shopify apps, public App Store apps, Shopify Functions, and checkout UI extensions — built by the engineers behind CartDrawer. We've been through Shopify's review process as a vendor, not just as a contractor.

Custom apps, public App Store apps, and integrations
Shopify Functions + checkout UI extensions (Plus)
Admin API, Storefront API, webhooks, embedded Polaris UIs
Fixed-scope quotes and post-launch maintenance

Conversion architecture

About our Shopify app practice

We build apps the way we build our own product

CartDrawer

Our own Shopify app

Functions + Checkout UI

Plus-native primitives

Fixed-scope quotes

No open-ended hours

San Francisco, USA

In-house engineers

Conversion is a Shopify app development agency headquartered in San Francisco. Alongside client work, we build and operate CartDrawer — our own Shopify app for cart and checkout conversion. That means the App Store review process, billing API, API version deprecations, merchant onboarding, and support load aren't things we've read about; they're things we run every week. Client apps get built with the same discipline.

Most Shopify app work falls into three shapes: integrations (ERP, PIM, 3PL, CRM, subscriptions), merchant-specific workflow automation, and customer-facing functionality via Functions, checkout UI extensions, and theme app extensions. We scope each to a fixed quote, build on Shopify's supported primitives rather than deprecated script injection, and hand over documented code your team can own.

Why Shopify apps fail

Three ways custom apps become liabilities

We inherit a lot of half-built Shopify apps. The failure patterns are consistent.

Built on deprecated primitives

Script tags, checkout.liquid customizations, and legacy REST endpoints that Shopify has already announced end-of-life for. The app works until the deprecation date, then breaks in production. We build on Functions, checkout UI extensions, and the GraphQL Admin API — the supported path forward.

Demo integrations, not production integrations

The ERP sync works in the demo with ten orders. Then Black Friday sends ten thousand, the webhook queue backs up, rate limits hit, and orders duplicate or vanish. We engineer for idempotency, retry, backpressure, and observability from the first commit.

No one to call when the API version changes

Shopify deprecates API versions quarterly. The freelancer who built the app has moved on, and nobody knows which calls will break. Every app we ship comes with documentation, monitoring, and a maintenance option so it keeps working as the platform evolves.

Have a Shopify workflow that needs an app?

Book a free 30-minute scoping call. We'll tell you whether it needs a custom app, a Function, a checkout extension, or an existing tool — and give you a fixed quote within 48 hours if it's a build.

30-minute call · No commitment · Custom quote in 48 hours

Shopify app development services

Every kind of Shopify app, built to last

Custom, public, and integration apps for Shopify and Shopify Plus — on the platform's supported primitives.

Custom Shopify App Development

Merchant-specific apps for workflows Shopify doesn't handle natively — custom order processing, fulfillment logic, reporting, internal tooling, and embedded admin UIs built with Polaris and App Bridge.

Embedded Polaris admin UIs
Custom workflow automation
Merchant-specific business logic
Multi-store support

Public App Store Development

Apps built to serve many merchants and pass Shopify's review: billing API, onboarding flows, GDPR webhooks, performance requirements, and the support tooling that keeps a listing healthy. We run our own — CartDrawer.

App Store review compliance
Billing API + plans
Onboarding + GDPR webhooks
Listing + support operations

Shopify Functions

Server-side customization of discounts, shipping rates, payment methods, cart and checkout validation, and order routing — running inside Shopify's infrastructure with no script injection.

Discount + bundle Functions
Shipping + delivery customization
Payment method rules
Cart + checkout validation

Checkout UI Extensions (Plus)

Custom fields, trust content, upsells, delivery instructions, and post-purchase offers rendered inside the native Shopify Plus checkout via checkout extensibility — the supported successor to checkout.liquid.

Checkout UI extensions
Post-purchase extensions
Branding API
Checkout.liquid migration

ERP, PIM, 3PL & CRM Integrations

Bidirectional sync with NetSuite, SAP, Dynamics, PIMs, warehouse systems, subscription platforms, loyalty tools, and CRMs — engineered for webhook reliability, rate limits, idempotency, and error recovery.

ERP + accounting sync
Warehouse + 3PL integration
PIM + catalog sync
Subscription + loyalty hooks

Storefront API & Headless Apps

Custom storefront functionality via the Storefront API — configurators, quote builders, B2B portals, and Hydrogen or Next.js components that need data Shopify's theme layer can't reach.

Storefront API integrations
Product configurators
B2B + quote portals
Hydrogen / Next.js components

Theme App Extensions

App-driven storefront features delivered as theme app extensions — installable blocks merchants place in the theme editor without touching Liquid, and that survive theme updates.

App blocks + embeds
Theme-editor configurable
Update-safe delivery
Performance-budgeted assets

App Maintenance & API Upgrades

Quarterly API version upgrades, dependency updates, monitoring and alerting, bug fixes, and small feature work on a retainer — so the app you launched keeps working as Shopify changes.

API version upgrades
Monitoring + alerting
Bug fixes + small features
Documentation upkeep

Shopify app tech stack

Built on Shopify's supported primitives

We build on what Shopify is investing in — not what it has announced end-of-life for.

Shopify platform

GraphQL Admin APIStorefront APIShopify FunctionsCheckout UI ExtensionsTheme App ExtensionsWebhooks + Bulk Operations

App framework

Shopify CLI + Remix app templatePolaris + App BridgeNode.js / TypeScriptPrisma + PostgresSession token auth

Operations

Billing API + subscriptionsGDPR mandatory webhooksQueue-backed webhook processingObservability + alertingApp Store review readiness

Our app development process

Scoped, built, reviewed, maintained

Discovery & scoping

A 30-minute call to understand the workflow, then a written scope: which Shopify primitives it needs, what data flows where, edge cases, and a fixed quote. If an existing app already solves it, we say so.

Architecture & build

Data model, API design, and Function or extension architecture agreed before code. Built on the Remix app template with Polaris, typed end-to-end, with webhook processing and error handling designed for production volume.

QA, review & launch

Tested against a development store and a staging copy of your production data. For public apps, we prepare the listing and take it through Shopify's review. Launch is monitored, not fire-and-forget.

Maintain & extend

Documentation and handover, then an optional maintenance retainer covering API upgrades, monitoring, and feature work. The app keeps working as Shopify's platform moves.

Why Conversion for Shopify apps

App developers who also operate an app

We run our own Shopify app

CartDrawer is our product. App Store review, billing, API deprecations, merchant support — we deal with all of it as a vendor, which is why client apps get built for the long run.

Supported primitives only

Functions, checkout UI extensions, theme app extensions, and the GraphQL Admin API. No script tags, no checkout.liquid, no REST endpoints Shopify has scheduled for removal.

Production-grade integrations

Idempotent webhook processing, queue-backed sync, rate-limit handling, and observability from the first commit — the difference between a demo integration and one that survives peak season.

Fixed-scope quotes

A written scope and a fixed price after discovery. No open-ended hourly billing on a project whose end you can't see.

Conversion-minded by default

Because we also run CRO and Shopify development, customer-facing app features are built with conversion and performance budgets in mind — not just functionality.

Documented handover

Every app ships with architecture docs, environment setup, and runbooks. Your team can own it, or we can maintain it — either way, nothing lives only in one developer's head.

Frequently asked

Shopify app development questions

What does a Shopify app development agency do?

A Shopify app development agency designs, builds, and maintains apps that extend what a Shopify store can do — either custom apps built for a single merchant's workflow, or public apps distributed through the Shopify App Store. That covers Admin API and Storefront API integrations, Shopify Functions (discounts, shipping, payment customizations), checkout UI extensions on Plus, theme app extensions, webhooks, embedded admin UIs built with Polaris, and the hosting, billing, and review-compliance work that keeps an app live.

What is the difference between a custom app and a public app?

A custom app is built for one store (or one organization's stores) and installed directly — no App Store listing, no Shopify review, and it can use merchant-specific logic. A public app is listed on the Shopify App Store, must pass Shopify's review, uses Shopify's billing API, and is built to serve many merchants. Most merchant needs are best served by a custom app; a public app is a product business. We build both, and we run our own public app, CartDrawer.

How much does Shopify app development cost?

Custom Shopify apps typically range from $8K–$25K for a focused integration or workflow automation, up to $40K–$150K+ for complex apps with embedded admin UIs, multi-store logic, or heavy third-party integrations. Public App Store apps usually start around $50K once billing, onboarding, review compliance, and support tooling are included. We scope to a fixed quote after a discovery call rather than billing open-ended hours.

Do you build Shopify Functions and checkout UI extensions?

Yes. Shopify Functions let us customize discounts, shipping rates, payment methods, and cart validation with server-side logic that runs inside Shopify's infrastructure. Checkout UI extensions (on Shopify Plus) let us add fields, content, upsells, and trust elements inside the native checkout. Both replace the old script-injection approaches with supported, forward-compatible primitives — and both are core to our CartDrawer and checkout optimization work.

Can you integrate Shopify with our ERP, PIM, 3PL, or CRM?

Yes. Integration apps are the most common thing we build: bidirectional sync with ERPs (NetSuite, SAP, Microsoft Dynamics), PIMs, warehouse and 3PL systems, subscription platforms, loyalty tools, and CRMs. We handle webhook reliability, rate limiting, idempotency, and error recovery — the parts that separate a demo integration from one that survives a Black Friday order spike.

Do you maintain apps after launch?

Yes. Shopify deprecates API versions on a quarterly cadence, changes review requirements, and ships new primitives regularly. We offer maintenance retainers covering API version upgrades, dependency updates, monitoring, bug fixes, and small feature work — so the app you launched keeps working as the platform moves.

Why hire an agency instead of a freelance Shopify app developer?

Freelancers work well for small scripts and single-endpoint integrations. For anything with an embedded admin UI, billing, multi-store logic, review compliance, or a launch deadline, an agency brings design, engineering, QA, and ongoing maintenance as one accountable unit. We also ship our own app — CartDrawer — so we've been through Shopify's review process and App Store operations first-hand, not just as a contractor.

Related services

Apps are one part of a Shopify build

CartDrawer

Our own Shopify app for cart and checkout conversion — the product that taught us App Store operations first-hand.

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Shopify Checkout Optimization

Checkout UI extensions and Functions applied to the leak closest to revenue.

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Shopify Development Services

Custom theme development, Plus builds, and replatforming — the store your app runs in.

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B2B Ecommerce Agency

Wholesale portals, price lists, and ERP sync — the integrations B2B on Shopify Plus depends on.

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Ready to build?

Scope your Shopify app in one call

Book a free 30-minute scoping call. We'll tell you whether it needs a custom app, a Function, a checkout extension, or something off the shelf — and send a fixed quote within 48 hours if it's a build.

No credit card · No commitment · Pay only on results