# Shopify apps & integrations.

- URL: https://sevsolutions.com/services/app-development

Custom apps, public apps, checkout extensions, Shopify Functions, and ERP/3PL/CRM pipes — built where Shopify's defaults stop and your business logic begins. TypeScript-first, Polaris-compliant, and battle-tested at Plus scale.

- App framework: React Router
- Checkout / discount: Functions
- Admin + Storefront: GraphQL
- Ready infra: SOC-2

## Custom apps, public apps, everything.

- **Custom apps** (React Router, Polaris, TypeScript): Internal tools, ops dashboards, merchandising utilities — scoped to one store, deployed on your infra or ours. Built on Shopify's React Router app template, with Polaris UI. No shortcuts.
- **Public Shopify App Store apps** (Billing API, Review-ready, Listings): Launch-ready App Store submissions with billing (recurring + usage), partner listing, review flow, and support tooling. We've shipped apps that passed review on the first submit.
- **Checkout extensions** (UI Extensions, Functions, Post-purchase): Upsells, custom fields, validation logic, delivery rules — built on Shopify's Checkout Extensibility, not Scripts, which no longer run.
- **Shopify Functions** (Rust / AS, Wasm, Edge): Custom discount logic, delivery customizations, payment customizations — compiled to WebAssembly, executed on Shopify's edge, zero middleware latency.
- **ERP / OMS / 3PL integrations** (Bi-directional, Event-driven, Observable): NetSuite, SAP, Shiphero, ShipStation, Odoo, Microsoft Dynamics — bi-directional sync with replay, retries, dead-letter queues, and full observability.
- **Webhooks & event infrastructure** (BullMQ, Postgres, OpenTelemetry): Idempotent consumers, retries with backoff, dead-letter queues, audit trails. The boring stuff that keeps Plus brands online during peak traffic.

## Specified first, built in phases.

The process behind 20+ Discount Functions shipped in the last two years and our B2B builds on Shopify Plus. Discovery ends with a written spec you sign off before any code is written.

1. **Discovery & spec**: We document what the app must do, every system it touches and the edge cases. On a B2B build this takes about two weeks.
2. **Build in phases**: Checkout extensions, Functions, admin screens and integrations, one phase at a time. Each Function ships with its own test suite.
3. **Pilot & go-live**: We wire it into your ERP or other systems, go live with a pilot group or in batches, and watch the first weeks of real orders for edge cases.
4. **Handoff**: Each Function ships with its test suite, so your team can maintain it after handoff. Or we keep developing the app on a monthly retainer.

## Questions we hear

### How long does a Shopify app take?

It depends on the scope. From our published work: porting one Function from JavaScript to Rust takes 2–4 weeks; replacing one to three simple Scripts with Functions, 2–3 weeks; a mid-sized B2B build on Shopify Plus, about 14 weeks. Your dates are in the written spec.

### Custom app or public App Store app?

A custom app is built for one store: internal tools, ops dashboards, integrations. A public app is listed in the Shopify App Store, with billing, a listing and Shopify's review. We build both, and we've shipped apps that passed review on the first submit.

### Our discounts were built on Shopify Scripts. What now?

Scripts no longer run; Shopify Functions replace them. We list what each Script did, rank them by the revenue that depends on them, then rebuild, test and deploy them as Functions in batches. One to three simple Scripts take 2–3 weeks; 15 or more encoding B2B pricing are a 4–6 month project.

### Which ERPs and 3PLs do you connect?

NetSuite, SAP, Microsoft Dynamics, Odoo, ShipHero and ShipStation, among others. Every integration syncs both ways, with replay, retries and dead-letter queues, so a failed sync is retried or set aside for review instead of disappearing.

### JavaScript or Rust for Shopify Functions?

JavaScript for most Functions. Rust when a Function runs into Shopify's instruction limit or handles large carts: the same logic in JavaScript runs many more instructions, and Shopify strongly recommends Rust for large carts. We've shipped six Rust Functions to production.

### Who maintains the app after launch?

Either your team or us. Each Function ships with its test suite, so your team can maintain it after handoff; or we keep developing the app on a monthly retainer.