Founding Engineer - Equity Only

About Mosaic

E-commerce in the US reached $1.3 trillion in 2025, accounting for 22% of all retail sales and growing at 10% a year. Sixty-five percent of consumers research products online before making any purchase, whether online or in store.

Independent retailers have not meaningfully participated in the e-commerce shift. The infrastructure built for online retail assumes a level of operational scale most independent stores do not have: warehouses, logistics, and digital marketing capabilities. A well-run boutique or specialty shop may have loyal customers and real inventory worth finding, but limited ability to reach people nearby who start their search online.

Mosaic is a local commerce marketplace built to counter this reality. Shoppers find nearby stores and browse real-time inventory through our consumer app. Retailers connect their existing catalog and payment systems and manage their storefront through our retailer app. Discovery, checkout, and order management run through one integrated platform. We are launching in Brooklyn NY.

The Role

We are looking for a Founding Engineer to own the technical execution that takes Mosaic from a nearly complete product to a live, operating marketplace and beyond.

The platform is substantially built. What stands between us and launch is the completion of our e-commerce connector, end-to-end validation of the payment and order flows, and the operational readiness to support our first stores and customers. After launch, the role expands into platform hardening, feature development, and scaling as we grow into new neighborhoods and markets.

You will work directly with our CTO on architecture and design decisions. You will own day-to-day engineering execution. You set the standards, make the calls, and ship the work.

What You Will Work On

•           E-commerce connector: Complete and harden our Shopify integration, covering real-time inventory sync, the full order lifecycle, webhook reliability, and the edge cases that matter in a live marketplace. A detailed technical specification covers every scenario end-to-end. The primary work between now and launch.

•           Marketplace payments: Validate and stress-test end-to-end payment flows built on Stripe Connect, including split payments, refunds, cancellations, and settlement. Correctness is not optional when real money is moving.

•           Launch operations: Work alongside the founding team to onboard our first Brooklyn stores, respond to production issues in real time, and build the operational confidence to scale.

•           Backend platform: Node.js, TypeScript, Express, and MongoDB Atlas. A large, well-documented REST API covering the full commerce and order lifecycle.

•           Mobile apps: React Native and Expo across iOS and Android, covering neighborhood discovery and checkout on the consumer side and storefront management on the retailer side.

What We Are Looking For

•           Strong full-stack engineer with deep Node.js and TypeScript experience and a real production track record. You have built, shipped, and operated systems.

•           Payments experience in production. You understand what correctness looks like when real money is involved. Stripe experience is a strong plus; Stripe Connect experience even more so.

•           Comfort with third-party API integrations: webhooks, idempotency, retry logic, and the operational discipline to keep data in sync under real-world conditions.

•           React Native experience, or a strong React background with the appetite to own the mobile layer.

•           Product-minded and decisive under ambiguity. You make sound tradeoff decisions without waiting to be told what to build.

•           Genuine interest in the problem Mosaic is solving. These are real businesses, with real owners, operating on thin margins.

Nice to Have

•           Shopify platform experience: Admin API, embedded app development, or webhook integrations.

•           Marketplace or multi-vendor commerce experience.

•           Cloud infrastructure experience: Azure, AWS, or GCP, CI/CD pipelines, and background job systems.

•           Geospatial or location-based feature development.

The Commitment

We expect 20 or more hours of committed, focused work per week. In return, you get a real equity stake in what we build together, direct input into engineering decisions, and a genuine say in the team and culture we grow into.

Equity and Compensation

•           Equity: 5% to 10% founding equity stake, commensurate with experience and contribution.

•           Vesting: 6-month cliff from your start date, then monthly vesting over a 4-year total term.

•           Salary: You will be a founding team member and equity holder. Compensation formalizes to a competitive full-time salary at our Series A.

Where We Are

Here is where we stand:

•           Consumer app: 95% complete and tested

•           Retailer app: 90% complete and tested

•           E-commerce connector: In active development, with a comprehensive technical specification covering every scenario end-to-end

•           15 independent Brooklyn stores committed and ready to onboard at launch

•           Angel investor engaged and committed to participate at launch

The Founding Team

Stefano, CEO and Co-Founder

Stefano began his career as a rocket scientist, developing satellite instruments for earth observation and deep space exploration. He then spent a decade leading product strategy for technology companies, working on multi-sided platform products including a KYC marketplace and a supply chain information-sharing network. He brings systems-level thinking and commercial strategy to a problem that requires both.

CTO and Co-Founder

Our CTO brings 20+ years of experience designing and delivering enterprise-scale technology systems across complex, high-availability environments. They designed and built the Mosaic platform from the ground up: the backend architecture, the marketplace payment infrastructure, and the mobile applications. They lead technical direction and work closely with the founding engineer on the decisions that shape the platform.

Tech Stack

Node.js  |  TypeScript  |  Express  |  MongoDB Atlas  |  Stripe Connect  |  React Native  |  Expo  |  Redux Toolkit  |  Azure  |  GitHub Actions  |  Shopify  |  iOS Dev  |  Android Dev  |  Stripe  |  Python  |  JavaScript  |  Rest APIs  |  GraphQL

How to Apply

Send your CV and a short note on why this resonates with you to [email protected]. GitHub or portfolio links are welcome.