Shopify and BigCommerce apps, checkout customization and integrations that keep products, inventory and orders correct everywhere you sell.

Store owners on Shopify or BigCommerce, Shopify app companies, and agencies that build for Shopify stores.

Your store needs a feature that no existing app provides.

Your checkout needs custom fields, rules, discounts or delivery and payment options.

Your discount, shipping or payment logic still lives in Shopify Scripts and needs to move to Shopify Functions.

You sell wholesale on Shopify Plus and need B2B behavior the built-in features do not cover.

Products, inventory or orders get out of sync between your store, marketplaces and other systems.

Custom and public Shopify apps, from the first version to App Store publishing.

Checkout UI Extensions and Shopify Functions for discounts, delivery and payment rules.

Shopify Plus B2B features and Scripts to Functions migrations.

BigCommerce apps and Multi-Storefront features.

Product, inventory and order sync with webhooks and background jobs that retry safely.

Shopify API version updates, including REST to GraphQL.

Fix and improve, from $400, delivered in about 3 days: fixes, updates and improvements to your store, app or checkout, tested and installed.

New feature, from $800, delivered in about 1 week: one complete feature, such as B2B rules, a checkout change or an integration.

Custom Shopify app, from $3,000, delivered in about 2 weeks: your own app, built around how your store works, with 14 days of fixes.

Care plans: app care $400 a month (API updates, testing and fixes), or store care $600 a month (up to 12 hours of support and fixes).

Ongoing work: part-time (20 hours a week) from $3,000 a month, or full-time (40 hours a week) from $6,000 a month. Monthly contracts get a lower rate because the hours are guaranteed.

Pay by the hour, or get a fixed price for a project, agreed before I start.

Understand the gap, and check whether a Shopify setting or an existing app already covers it, so you do not pay for code you do not need.

A written plan: APIs, extensions, webhooks, access scopes and risks.

Build and test on a development store before anything touches your live store.

Launch on your store, or submit for App Store review.

Support as Shopify's APIs and your store change.

Five published Shopify App Store apps I worked on as part of a team, three also on BigCommerce: structured data and SEO, real-time product, inventory and order sync, country-based redirects and fake email detection.

An Amazon SP-API import and sync system for listings, variants and images (client work).

4+ years building Shopify and BigCommerce apps in Rails and React for US clients.

More: https://mjesar.github.io/services/shopify-development/