Build Custom & Public Shopify Apps that Scale
Paying monthly for off-the-shelf apps that only half-fit? We build every kind of Shopify app — from custom apps (our specialty) to public App Store apps, embedded admin tools, and Checkout, Customer Account & POS extensions plus Shopify Functions — that do exactly what your store needs. Code you own, built by a senior team to scale.
Built on the modern Shopify stack
React
Remix
Next.js
Node.js
TypeScript
Shopify
GraphQL
Polaris
Web ComponentsWe're the Experts in Shopify App Development
When Shopify's 8,000+ apps still can't do what your store needs — or three of them conflict and slow your site — a custom build is the answer. FlowCart Agency is a specialized Shopify app studio: a senior team that designs, builds, scales, and maintains every kind of Shopify app. Our core strength is custom (private) apps built around your exact workflow — but we also ship public App Store apps, embedded admin tools, and the full range of Checkout, Customer Account, POS, and Function extensions.
Why work with us?
20+ Shopify stores served across D2C, B2B, and subscription brands worldwide.
Revenue-focused engineering that moves a real metric — AOV, conversion, or retention.
5-star client relationships built on senior, direct communication and long-term partnerships.
End-to-end app development from concept and design to publish, monitoring, and ongoing updates.
Types of Shopify Apps, Extensions & Functions we build.
Whatever your store can't do today — an integration, an automation, a checkout tweak, or a whole new revenue stream — one of these solves it. Start here, then read the guide for whichever fits.
Custom Apps for Merchants
Custom apps built exclusively for your store — ERP integrations, ops automation, and workflows tailored to how your business actually runs. (Shopify retired private apps in 2022; custom apps replaced them.)
Public Apps on the Shopify App Store
Got a Shopify app idea worth selling? We take it from concept and design to development, App Store approval, and launch — built to get listed, win installs, and monetize at scale.
Embedded Admin Apps
Custom tools that live right inside your Shopify Admin — dashboards, bulk actions, and workflows that save your team hours of manual work every week and feel completely native, no tab-switching required.
Theme App Extensions
Inject UI into your storefront without editing theme code. App blocks and embeds for banners, badges, preorder buttons, and more — merchant-friendly and theme-safe.
Checkout UI Extensions
Turn the highest-intent moment in your funnel into more revenue — native upsells, order bumps, custom fields, and trust badges built right into the Shopify Plus checkout: fast, on-brand, and upgrade-safe.
Customer Account UI Extensions
Customize the customer account area — add tabs, pages, and tools that turn first-time buyers into loyal repeat customers.
POS UI Extensions
Extend the Shopify POS app for your retail stores — custom checkout actions, employee tools, and analytics widgets that connect online and in-store.
Cart Transform & Discount Functions
The cart and checkout logic that lifts average order value — bundles, tiered and BOGO discounts, auto-add free gifts, and dynamic pricing — running natively on Shopify Functions for instant, reliable results.
Build vs buy
When do you need a custom Shopify app?
Off-the-shelf apps are great — until they aren't. If any of these sound familiar, a custom Shopify app will almost always serve you better than forcing an App Store tool to fit.
An app almost works — but not quite
You've found an app that does 80% of what you need, but the missing 20% is exactly the part that matters. A custom app does 100% of your job, your way.
You're stacking overlapping apps
Paying $500+ a month across a dozen apps that half-overlap and half-conflict? One custom build can replace the stack — and pay for itself over time.
Apps are slowing your store down
Every off-the-shelf app injects its own scripts on every page. A lean custom app does one job fast, without dragging down your speed and Core Web Vitals.
You need a workflow no app offers
A unique pricing rule, bundling logic, subscription model, or automation that nothing on the App Store handles the way your business actually works.
You need to connect Shopify to another system
An ERP, CRM, 3PL, POS, or custom backend that has to sync with Shopify in real time — built as a reliable integration instead of a fragile workaround.
You want to build & sell a public app
Launch your own app on the Shopify App Store as a product and revenue stream — built to Shopify's Built-for-Shopify standards from day one.
Straight answer
Most stores don't need a custom app.
The App Store is genuinely good, and a $29/month subscription usually beats owning software. We'll tell you when that's your answer — it costs us the project and saves you the budget.
Build custom if…
- An App Store app gets you most of the way, but the missing part is the part that makes you money.
- You're paying for several overlapping apps and still doing the joining-up by hand.
- Shopify has to stay in sync with an ERP, CRM, 3PL or warehouse system in real time.
- The logic you need is specific to how your business prices, bundles or fulfils orders.
Buy off the shelf if…
- A well-reviewed app already does the job. Paying $29 a month beats owning a codebase.
- You need it live next week. A custom build is measured in weeks, not days.
- The requirement is still changing. Settle what you actually need before paying to hard-code it.
- Nobody on your side will own the app after launch — custom software needs a home.
In detail
Every kind of Shopify app, engineered.
What each one does, what it costs you in complexity, and when it's the wrong answer — so you pick the right surface before anyone writes code.
Custom Apps for Merchants
Custom apps built exclusively for your store — ERP integrations, ops automation, and workflows tailored to how your business actually runs. (Shopify retired private apps in 2022; custom apps replaced them.)
Custom Integrations
Connect your store to ERPs, CRMs, 3PLs, and internal tools.
Enhanced Workflows
Automate complex tasks like inventory, order fulfillment, or reporting.
Store-Specific Features
Build the unique features that set your store apart — no off-the-shelf app required.
Public Apps on the Shopify App Store
Got a Shopify app idea worth selling? We take it from concept and design to development, App Store approval, and launch — built to get listed, win installs, and monetize at scale.
End-to-End Consultation
From ideation and user flow design to marketing and listing optimization.
Full Lifecycle Support
Ongoing updates, maintenance, and feature enhancements to keep your app competitive.
Revenue Generation
Reach Shopify's millions of merchants and grow recurring app revenue.
Embedded Admin Apps
Custom tools that live right inside your Shopify Admin — dashboards, bulk actions, and workflows that save your team hours of manual work every week and feel completely native, no tab-switching required.
Custom Dashboards
Real-time data, KPIs, and team views your team actually uses daily.
Bulk Operations
Mass-edit products, orders, customers, and metaobjects without slowing down.
Analytics & Reporting
Custom reports tailored to your store's KPIs and exportable for your team.
Theme App Extensions
Inject UI into your storefront without editing theme code. App blocks and embeds for banners, badges, preorder buttons, and more — merchant-friendly and theme-safe.
App Blocks
Drag-and-drop blocks merchants can add to any page from the theme editor.
App Embeds
Site-wide functionality — banners, popups, sticky bars, badges.
Theme-Safe Updates
No theme conflicts. Survives theme switches and Shopify updates.
Checkout UI Extensions
Turn the highest-intent moment in your funnel into more revenue — native upsells, order bumps, custom fields, and trust badges built right into the Shopify Plus checkout: fast, on-brand, and upgrade-safe.
Custom Fields & Inputs
Add gift messages, PO numbers, delivery notes, or referral codes.
Upsell & Cross-sell Blocks
Increase AOV with smart product recommendations at checkout.
Trust & Compliance
Trust badges, age verification, terms acceptance — fully native.
Customer Account UI Extensions
Customize the customer account area — add tabs, pages, and tools that turn first-time buyers into loyal repeat customers.
Custom Account Tabs
Add 'My Subscriptions', 'Returns', 'Loyalty', or 'My Details' tabs.
Self-Service Tools
Order tracking, returns, refunds, and profile editing — all in one place.
Engagement Surfaces
Loyalty status, reward points, and personalized offers in-account.
POS UI Extensions
Extend the Shopify POS app for your retail stores — custom checkout actions, employee tools, and analytics widgets that connect online and in-store.
Custom Checkout Actions
Add buttons for loyalty lookup, gift wrapping, custom discounts.
Employee Tools
Staff permissions, shift management, and employee performance leaderboards.
Floor Analytics
Real-time KPIs, hourly sales, and performance widgets at the counter.
Cart Transform & Discount Functions
The cart and checkout logic that lifts average order value — bundles, tiered and BOGO discounts, auto-add free gifts, and dynamic pricing — running natively on Shopify Functions for instant, reliable results.
Cart Transform Function
Server-side cart logic — bundles, hidden line items, variant expansions.
Discount Functions
Tiered pricing, BOGO, bundle discounts, customer-specific deals.
AJAX & Storefront API
Frontend JS — auto-add free products, live cart updates, custom logic.
Not sure which type of app or extension fits your idea?
Tell us the problem you're solving and we'll recommend the right approach — no jargon, no upselling.
How We Build Your Shopify App.
From concept to App Store in four steps. We keep you in the loop at every stage so you ship with confidence.
Discovery & strategic roadmap
We start with your product vision, technical constraints, and business goals. You leave with a clear scope, milestones, and success metrics.
What you'll get
- Discovery & strategy
- Technical roadmap
- Scope & success metrics
UX that merchants actually love
Every flow is prototyped in Figma and reviewed with you before we write a single line of production code — UX that's intuitive for merchants, not just good-looking.
What you'll get
- UI/UX prototyping in Figma
- Polaris-aligned admin design
- Brand consistency end-to-end
Senior engineering, agile delivery
Modern stack (React, TypeScript, Node, Remix) with weekly demos. You see features working before they ship.
What you'll get
- Clean, documented code
- Agile sprints with weekly demos
- Testing & quality assurance
Launch and beyond
App Store submission against Shopify's checklist, GitHub-based release process, and an ongoing maintenance plan from day one.
What you'll get
- Version control via GitHub
- App Store submission
- Ongoing maintenance & updates
Apps we've built
Real Shopify apps shipped
A look at custom apps we've delivered for merchants and the public apps we're launching on the Shopify App Store.
Results You Can Expect
Increased Efficiency
Apps that automate the manual work — saving your team hours every week.
Scalable Solutions
Architecture that handles 10K orders or 10M without rewrites.
Improved Conversion & Sales
Storefront extensions and checkout features that lift AOV and checkout conversion.
Global Reach
Multi-region, multi-language, multi-currency — built in from the start.
Explore next
Other things we do
Most stores need two or three of these working together. Book a call and we'll tell you which ones actually move your numbers.
- Shopify Theme DevelopmentCustom themes built from Figma to production Liquid on Online Store 2.0 — fast and merchant-editable.
- Shopify MigrationMove from WooCommerce, Magento or BigCommerce with a full 301 redirect map and zero downtime.
- Shopify SEOTechnical audits, Core Web Vitals, structured data and collection content built around buyer intent.
- Shopify Performance OptimizationFaster load times and green Core Web Vitals — theme refactors, image pipelines and app cleanup.
- Shopify A/B TestingHypothesis-led experiments on product pages and checkout, shipped as native theme code.
- Shopify Email Marketing & KlaviyoFlows, segmentation and campaigns — welcome, abandoned cart, winback and SMS, built and monitored.
- Shopify CRO & FunnelsValue-ladder, tripwire, quiz and post-purchase upsell funnels built to lift conversion and AOV.
- Shopify Maintenance & SupportRetainers covering uptime monitoring, security patching, bug fixes and proactive improvements.
Frequently asked questions
- Most custom apps ship in 4–8 weeks; public App Store apps with review take 8–14 weeks including Shopify's review window. We give a firm timeline after a discovery call.
Ready to start building your Shopify app?
Get a clear scope, fixed quote, and a concrete plan within 48 hours. We'll review your idea and tell you honestly whether we're the right team.
Start your app build