SeniorFullstackEngineer

This role is open to candidates based in LATAM, Africa, and Eastern Europe. Please note that as this role supports U.S.-based clients, candidates must be available to work during U.S. business hours aligned with the client’s time zone.   Client Overview Our client is a fast-moving marketing measurement and attribution technology company that empowers e-commerce brands to make smarter, data-driven advertising decisions. Their platform combines a robust Rails API, a modern React frontend, and a Python-powered data and ML infrastructure — all operating across a 20+ repository workspace where AI agents and engineers collaborate side by side to ship product at speed. They are a team that values engineering craft, architectural clarity, and a bias toward simplicity, and they are looking for senior engineers who raise the bar through code review, documentation, and thoughtful system design as much as through feature delivery. Role Overview The Senior Fullstack Engineer will own and elevate engineering quality across a multi-repo platform that spans a Rails API, React frontend, and Python data and ML services. This role sits at the intersection of backend architecture, frontend delivery, and data platform development, making it ideal for a polyglot engineer who is energized by ambiguity and cross-service complexity. The Senior Fullstack Engineer will also mentor fellow engineers, establish best practices, and help design agent-readable systems as AI-assisted development becomes a core part of how the team operates. Location Fully Remote (Work from Home) | 9AM - 5PM EST Key Responsibilities Backend Development   - Design and ship production features on the Ruby on Rails API, including authentication flows, background jobs via Sidekiq, and PostgreSQL schema design. - Maintain and improve API contracts using OpenAPI or JSON:API standards consumed by SPA frontends. - Write and enforce test coverage using RSpec, maintaining high reliability across services.   Frontend Developmen