Fospha is dedicated to building the world's most powerful measurement solution for online retail. For over a decade, we've helped teams make smarter decisions with full-funnel marketing insights, forecasting, and optimisation. With Fospha, every team moves faster and grows smarter. Trusted by leading brands across three continents, including Gymshark , Huel and Oh Polly, Fospha manages $4 billion in annual ad spend. We're scaling fast across London, Mumbai, and Austin – and we're now looking for a Senior Software Engineer to join our Team! The Role As a Senior Software Engineer, you'll build the products our customers rely on every day to make multi-million dollar media decisions. You'll work across the full stack - from crafting responsive, intuitive frontend experiences through to designing and scaling the backend microservices that power them - and, given the seniority of this role, you'll also help shape system design and infrastructure decisions as we scale. You'll work alongside engineers, product managers, and AI agents as part of our AI-first operating model, where lean, high-autonomy teams ship fast and learn faster. This is a hands-on engineering role for someone who's comfortable owning a feature end-to-end - from initial design through to production - and who wants to grow their craft in a fast-moving, ambitious environment. Where you'll focus • Frontend development using modern JavaScript frameworks (React.js or Next.js) • Backend development using Python-based microservices • System design and infrastructure, contributing to architectural decisions as we scale • End-to-end feature ownership across the stack • (Nice-to-have) Exposure to Data Science / Data Engineering workflows Key Responsibilities • Design, build, and maintain full stack features - from frontend UI/UX through to backend services and APIs in Python. • Contribute to system design and infrastructure decisions, helping evolve our