Senior Software Engineer - E-Commerce Systems

Simplex; New York (NY); On-site; USD 220,000 - 300,000; Full time

Benefits offered by this job

Medical & Dental

401(k)

Catered lunches and dinners

Job summary

Simplex is seeking a founding engineer for our eCommerce build. You will own systems connecting an online cart to a physical store: catalog, inventory sync, checkout, and order fulfillment.

Work with Platform Engineering and Money Movement, partnering with store owners to ensure online orders show up reliably and on time.

Qualifications

• 5+ years building production software with web frontends.
• Experience shipping eCommerce systems end to end: catalog, cart, checkout, orders.
• Depth in PostgreSQL: schema design, transactions, and high concurrency.
• Fluency with transactional guarantees: idempotency, retries, and out-of-order events.

Responsibilities

• Build merchant storefronts with fast, SEO-friendly Next.js storefronts.
• Own real-time inventory sync between in-store POS and online channels.
• Design online checkout and order management with card-not-present payments and refunds.
• Build pickup and local delivery fulfillment and notifications.
• Extend delivery-app and marketplace integrations to use one truth source.

Skills

TypeScript/Node

Full-stack

eCommerce

PostgreSQL

Transactions/Idempotency

Frontend UX

Tools

Next.js

tRPC

Prisma

Vercel

ElastiCache

RDS / RDS Proxy

Job description

Our client is a Series A point-of-sale software company in NYC, building the #1 operating system for local retailers. Our platform runs the entire store: point-of-sale, integrated payments, eCommerce, inventory management, delivery-app integrations, marketing, bookkeeping, and AI agents. It lets the owners of liquor, grocery, and convenience stores compete like the big chains without losing what makes them local.

We move fast and ship daily. Every feature lands in real stores the same week, and our customers call us by name. AI-assisted engineering isn't a talking point here. Agents like Devin, Claude, and Codex are part of how the team works every day, and engineers who master that leverage ship multiples of what they could alone.

About the Team

eCommerce owns everything that lets a merchant sell beyond the four walls of the store: online storefronts, pickup and delivery ordering, and marketplace and delivery-app channels.

Our merchants already run every sale, every shelf, and every drawer count through our platform. Their customers expect to browse that same shelf from their phone, order a bottle for pickup in 20 minutes, or get a case delivered tonight. This team turns the store's live inventory into a shopping experience that never sells something that isn't on the shelf.

About the Role

You'll be one of the founding engineers on our eCommerce build. You'll be a technical owner of the systems that connect an online cart to a physical store: catalog, real-time inventory sync, online checkout, and order fulfillment.

This means designing for the edge cases that only exist in omnichannel retail. Examples: the last bottle sold in-store while it sits in an online cart, a substitution that changes the order total after authorization, an age check at handoff. You'll partner closely with Platform Engineering, whose sale write path and payments layer your orders run through, and with Money Movement, whose ledgers handle gift cards and loyalty. You'll also work directly with store owners who will judge you on whether online orders actually show up.

In this role, you will

• Build merchant storefronts from the ground up: fast, SEO-friendly Next.js shopping experiences generated from each store's live POS catalog, with no separate product setup
• Own real-time inventory sync between in-store POS and online channels across multi-location retailers, including reservations, oversell prevention, and graceful handling when a shelf count is wrong
• Design online checkout and order management: card-not-present payments, preauth and capture when substitutions change the total, refunds, and order states that stay correct under retries and concurrent edits
• Build pickup and local delivery fulfillment: order routing to the right location, picking workflows for store staff, substitutions, and customer notifications
• Extend our delivery-app and marketplace integrations (menus, pricing, availability, order ingestion) so every channel runs off one source of truth
• Build compliance into the flow for age-restricted products, including ID verification at checkout and handoff and location-specific selling rules
• Unify promotions, loyalty, and gift cards across in-store and online so a customer's balance and discounts work everywhere
• Partner with Applied AI on catalog enrichment (product images, descriptions, and categorization) and on recommendations that help merchants sell more online
• Multiply your output with AI agents: direct, review, and productionize agent-written code as a core part of your workflow

Your background looks something like this

• 5+ years building production software, with deep experience in TypeScript/Node full-stack systems, including customer-facing web frontends
• Experience shipping eCommerce systems end to end: catalog, cart, checkout, and order management in production with real order volume
• Practical fluency with transactional guarantees: idempotency, retries, and what happens when an order webhook arrives twice or out of order
• Real depth in PostgreSQL: schema design for catalogs and orders, transactions under concurrency, and queries that stay fast as SKU counts grow
• A product instinct for shoppers and store staff alike: you care whether checkout feels instant and whether the picker in the back room can find the item
• Comfort operating with high ownership in a small team where your decisions become the standard

Even better

• Omnichannel or buy-online-pickup-in-store (BOPIS) experience, especially syncing physical inventory with online channels
• Integrations with delivery apps or marketplaces (DoorDash, Uber Eats, Instacart, or similar)
• Experience selling age-restricted products online (alcohol, tobacco) and the compliance that comes with it
• Payments experience: card-not-present flows, tokenization, preauth/capture, or PCI-adjacent systems
• Storefront performance and SEO: Core Web Vitals, structured product data, and pages that rank
• Familiarity with our stack: Next.js, tRPC, Prisma, Vercel, ElastiCache, RDS/RDS Proxy
• Experience directing AI coding agents (Claude Code, Cursor, Codex, Devin) and building the guardrails that make them safe at scale
• Retail or POS domain experience, especially grocery, liquor, or multi-location operations

Compensation

$220k – $300k base + meaningful equity

This range reflects the expected compensation for this role. Compensation within the range is determined based on experience, skills, and scope of responsibilities. In addition to base salary, we offer meaningful early-stage equity.

Benefits

• Fully company-covered medical and dental benefits
• 401(k)
• Catered lunches and dinners: dinner is provided each evening for employees who'd like to eat and connect with the team, and lunch is provided weekly

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