Fullstack AI Developer

Upsellplus; New York (NY); Hybrid; USD 55,000 - 70,000; Full time

Job summary

UpsellPlus is seeking a skilled fullstack developer to own complete features across frontend, backend, data, and third‑party integrations. You will work directly with the CTO and have substantial ownership over what you build and how it reaches production.

This role requires delivering end‑to‑end features, including design, implementation, testing, release, and monitoring, with minimal overhead and strong customer focus.

Qualifications

• Experience delivering fullstack web applications in production.
• Experience with Shopify APIs, webhooks, themes, and checkout extensions is valuable.
• Ability to design, implement, test, release, and monitor features end-to-end.

Responsibilities

• Own complete features across frontend, backend, data, and integrations.
• Ship production features with testing, monitoring and rollback planning.
• Work closely with CTO and founder to align with customer needs and product goals.

Skills

Fullstack development

Shopify APIs

Webhooks

Themes

Checkout extensibility

App extensions

Merchant data

Job description

UpsellPlus helps Shopify brands increase their average order value and conversion rate through intelligent product recommendations and upsells.

More than 300 brands use our products across millions of orders. We are building toward an AI-powered conversion optimization system that can understand a store, identify revenue opportunities, and help merchants launch and improve offers.

We are a small engineering team. You will work directly with our CTO and have substantial ownership over what we build and how it reaches production.

Why we're hiring

We want to ship more high-quality product without creating unnecessary process or management overhead.

We are hiring a fullstack developer who can take a well-defined customer or business problem, work through the technical decisions with our CTO, and independently deliver the solution across the stack.

This is not a role for someone who only wants to implement isolated tickets. You will own complete features: understanding the problem, designing the solution, writing the code, testing it, releasing it, monitoring it, and improving it using real customer feedback.

What success looks like

Within your first 90 days, you will:

• Understand the product, architecture, development workflow, and critical customer journeys.
• Make a meaningful production contribution within your first 10 business days.
• Independently own and ship a scoped customer-facing feature within your first 30 days.
• Ship at least one substantial feature or product improvement within 90 days.
• Deliver production work with appropriate testing, monitoring, documentation, and rollback planning.
• Diagnose and resolve production problems without needing step-by-step direction.
• Use AI development tools to increase speed while maintaining engineering quality.
• Earn the team’s confidence that you can own an important product area from problem to production.

We value speed, but we do not define speed as writing code quickly. Speed means delivering useful, reliable software with minimal rework.

• Turn product requirements and customer problems into technical plans.
• Build complete features across frontend, backend, data, and third‑party integrations.
• Make pragmatic architecture decisions appropriate for a growing SaaS product.
• Break large projects into small, releasable increments.
• Review feature performance after launch and iterate based on evidence.
• Build experiences that operate reliably inside the Shopify ecosystem.
• Work with Shopify APIs, webhooks, themes, checkout extensibility, app extensions, and merchant data.
• Design around Shopify’s platform constraints and review requirements.
• Ensure features work across different themes, stores, markets, devices, and configurations.

Prior Shopify development experience is valuable, but exceptional fullstack engineers can learn the platform.

AI-powered product capabilities

• Integrate language models and other AI services into real customer workflows.
• Build systems that turn store and performance data into useful recommendations.
• Evaluate model outputs for quality, reliability, latency, and cost.
• Design fallbacks and safeguards for imperfect AI behavior.
• Distinguish between a useful AI capability and an impressive-looking demo.

Reliability and engineering quality

• Write clear, maintainable code.
• Add tests proportional to the risk and importance of the change.
• Improve observability, error handling, and production diagnostics.
• Participate in code review and help improve engineering standards.
• Investigate root causes instead of repeatedly treating symptoms.
• Protect customer data and consider security throughout development.

Product and customer judgment

• Understand why a feature matters commercially.
• Speak directly with customers when necessary to understand a problem.
• Work closely with the CTO, customer success team, and founder.
• Challenge unnecessary complexity and propose simpler solutions.
• Take responsibility for the customer outcome, not only technical completion.

What you'll own

• You have repeatedly shipped and maintained fullstack web applications in production.
• You can work comfortably across frontend, backend, databases, APIs, and infrastructure.
• You have experience designing and integrating third‑party APIs.
• You can independently investigate unfamiliar systems and solve ambiguous problems.
• You understand testing, monitoring, performance, security, and production operations.
• You use AI coding tools effectively while carefully reviewing and validating their output.
• You communicate clearly and document important technical decisions.
• You prefer ownership and execution over meetings and elaborate process.

Experience with Shopify, ecommerce, recommendation systems, experimentation platforms, high-volume event data, or production AI applications is a meaningful advantage.

This role is probably not for you if

• You want every task fully specified before beginning.
• You only want to work on the frontend or backend.
• You consider a feature complete when the code is merged.
• You optimize for lines of code or ticket volume rather than customer value.
• You use AI‑generated code without understanding or validating it.
• You need a large product, QA, or infrastructure team around you to ship safely.
• You enjoy architecture discussions more than releasing software.

How we work

• Engineers own features through production.
• Planning is collaborative; execution is independent.
• Progress is more important than process.
• Simplicity is a feature.
• AI is a development multiplier, not a substitute for engineering judgment.
• We communicate directly, document decisions, and keep meetings limited.

Remote · $55–70k USD base + performance compensation

Launch your first offer with a 14‑day free trial, or talk with our team about a Shopify Plus strategy.