Senior Fullstack Engineer

We are seeking exceptional Senior Fullstack Engineers with deep expertise in client-side development to build our next-generation merchant experience platform. This role primarily focuses on: Client-side SDK development, Multi-tenant architecture, Enterprise integration frameworks and High-performance frontend systems.

You will also contribute strategically to backend systems, including data modeling, infrastructure planning, and scalable deployment architecture.

This role is ideally based in Seattle, the Bay Area, or Austin, with flexibility for exceptional candidates., * Client-Side Platform & SDK Development: Design and implement reusable, distributed JavaScript/CSS SDK frameworks that enable seamless merchant integration across diverse retail environments. Build scalable multi-tenant frontend architecture that supports enterprise-grade customization and performance.

• Frontend Engineering: Develop high-performance, scalable, and accessible web applications using React, Next.js, and Tailwind CSS. Implement modern rendering strategies (SSR, SSG, ISR) to ensure optimal SEO and performance.
• API & Backend Integration: Partner with backend engineers to integrate frontend logic with RESTful APIs and GraphQL services. Ensure secure, resilient communication between client-side SDKs and backend systems.
• Performance & Scalability Optimization: Drive performance improvements through code splitting, lazy loading, image optimization, caching strategies, and runtime efficiency tuning.
• Code Quality & Standards: Write clean, maintainable, and reusable code. Enforce best practices for accessibility (a11y), SEO, modular architecture, and automated testing.
• Backend & Infrastructure Support: Contribute to data modeling, database schema design, infrastructure planning, and cloud deployment (AWS/GCP). Support CI/CD processes and production monitoring.

• 5+ years of professional software development experience
• Proven experience building production-grade web applications in multi-tenant or enterprise environments
• Experience developing distributed client-side SDKs or embedded commerce tools is strongly preferred

Technical Skills

• Expert-level proficiency in JavaScript, TypeScript, and CSS
• Deep expertise in React, Next.js, and Tailwind CSS
• Proficient with the AI native coding tools such as cursor, codex and claude code
• Strong understanding of multi-tenant build systems and distributed JavaScript/CSS framework design.
• Experience with RESTful APIs and/or GraphQL integrations.
• Solid understanding of data modeling, database schema design, and backend architecture principles
• Familiarity with cloud infrastructure (AWS or GCP) and modern DevOps practices
• Strong understanding of frontend performance optimization and rendering strategies, * GenAI-native in how we build, sell, and operate
• High ownership, low overhead, and bias toward action
• Focus on speed, experimentation, and execution
• Deep emphasis on creating clear, demonstrable customer value
• Preference for builders and operators over hierarchy
• Strong belief in in-person collaboration

• Opportunity to build foundational platform technology at a fast-growing AI startup
• Direct impact on product architecture and technical direction
• Competitive salary with uncapped commission and equity
• Benefits: Health, dental, and vision insurance, 401(k), Unlimited PTO

Launched in 2025, Spangle AI is the agentic conversion layer connecting AI-led discovery to real-time conversion. We’ve partnered with enterprise brands like REVOLVE, Alexander Wang, and Steve Madden, delivering up to 50% conversion lifts and 2x ROAS improvements.

We recently closed a $15M Series A. Spangle won NRF’s VIP (Vendor in Partnership) Award for Best AI-Driven Marketing Solution and was recognized in Business of Fashion’s AI startups to Watch.

Founded by serial entrepreneurs with 30+ years scaling AI and commerce at Amazon, Saks, and Gap, we’re building the commerce infrastructure for the agentic era, where ChatGPT Shopping, Google AI Overviews, and Meta are reshaping how consumers discover and buy.