Senior Fullstack Engineer

Senior Fullstack EngineerAbout SpangleAILaunched 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.The RoleWe 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, infrastructureplanning, and scalable deployment architecture.This role is ideally based in Seattle, the Bay Area, or Austin, with flexibility for exceptionalcandidates.What you'll own: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.What We're Looking ForExperience5+ years of professional software development experienceProven experience building production-grade web applications in multi-tenant or enterprise environmentsExperience developing distributed client-side SDKs or embedded commerce tools is strongly preferredTechnical SkillsExpert-level proficiency in JavaScript, TypeScript, and CSSDeep expertise in React, Next.js, and Tailwind CSSProficient with the AI native coding tools such as cursor, codex and claude codeStrong 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 principlesFamiliarity with cloud infrastructure (AWS or GCP) and modern DevOps practicesStrong understanding of frontend performance optimization and rendering strategiesOur CultureGenAI-native in how we build, sell, and operateHigh ownership, low overhead, and bias toward actionFocus on speed, experimentation, and executionDeep emphasis on creating clear, demonstrable customer valuePreference for builders and operators over hierarchyStrong belief in in-person collaborationWhy SpangleOpportunity to build foundational platform technology at a fast-growing AI startupDirect impact on product architecture and technical...